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Abstract: Micro-3D printing utilizing two-photon lithography (TPL) is an enabling technology for developing novel miniaturized optical systems [1]. It offers unprecedented design freedom, flexibility, and high resolution, making it possible to fabricate complex miniaturized optical systems with unmatched accuracy.

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Abstract: Over the past several decades, advances in direct surface structuring have been accomplished using a variety of ultrafast laser approaches. Micromachined structures show dependence on the pulse length, chirp, polarization, vector polarization, and topological states of the laser pulses. All of these parameters allow one to control material modification, thereby introducing new machining capabilities. Of particular interest in the past decade is the use of cylindrical and vortex vector beams. One area that remains relatively unexplored is the use of pulses with time-evolving polarization states. Here, we explore the use of optical centrifuge pulses in photoablation of silica and silicon surfaces. Optical centrifuge pulses have linear polarization that undergoes angular acceleration to frequencies with Ω𝑜𝑐>6×1013 rad/s over the duration of the pulse. [1,2] My research group has used an optical centrifuge to prepare gas-phase molecules in extreme rotational states in order to investigate their collisional energy transfer and bimolecular reaction dynamics. [3-7] Here we turn our attention to the effect of such pulses on photoablation. The optical centrifuge pulses are created by splitting Ti:sapphire laser pulses into pairs of pulses with 𝜆0=805 nm. One pulse 𝜔1 has positive chirp and the other pulse 𝜔2 has negative chirp. Opposite circular polarization is induced in the pair of pulses before they are recombined in time and space to form the angularly accelerating linear optical field. The instantaneous angular frequency Ω𝑜𝑐 is determined by the time-dependent frequency difference of 𝜔1 and 𝜔2, where Ω𝑜𝑐(𝑡)=12[𝜔1(𝑡)−𝜔2(𝑡)]. This research compares photoablation for six polarization schemes: the optical centrifuge, a dynamic polarization grating, positively chirped pulses with linear or circular polarization, and negatively chirped pulses with linear or circular polarization.

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Abstract: Pulsed laser ablation (LAL) and pulsed laser fragmentation (LFL) in liquids are recognized as the foremost laser-based synthesis and processing methods, facilitating the synthesis of colloidal nanoparticles [1-3]. While LAL has demonstrated productivities approaching 10 g/h, LFL, despite exhibiting throughput one order of magnitude lower, offers access to substantially smaller nanoparticles with in the nanocluster size range(<3nm)[4]throughlaser-induced phase explosion of nanoparticles [5].In contrast, microparticle attrition operates via a distinctly different mechanism, reminiscent of particle crushing rather than complete evaporation, yet still affording access to the same nanoclusters. From an application standpoint, pulsed laser attrition of microparticles has the potential to surpass even advanced LALefficienciesbyoneorderofmagnitude[6]. The technical approach is simple: a microparticle dispersion is vertically flowing into the diameter-matched, horizontal laser beam, allowing fully continuous and robust operation. By precise alignment of the number of pulses per volume element (PPV), adjustable by matching the laser repetition rate with the particle dispersions jet flow velocity (residence time), the surface oxidation state of the ultrasmall particles can be adjusted [7], highly relevant for catalysis. This presentation aims to unveil the latest developments in scaling microparticle-LFL(laser crushing), providing application examplesofNIR-absorbingmaterialsforadditive manufacturing(LaB6-sensitizeddesktopNIR-LaserPowderBedFusion[8])and heterogeneous catalysis (water splitting by IrOx [6, 7]).

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Abstract: We show a simple method to deposit size-selected spherical nano/micro particles on the substrate using a pipe and gas flowing through the pipe. The particles ejected from the target by laser irradiation travel with gas flow through the pipe to the substrate. The deposited materials were spherical particles with a narrow size distribution. The mean diameter can be varied in the range of tens of nm to a few microns by controlling gas flow velocity. The mean diameter agreed well with the theory based on the inertial impaction on the substrate for many target materials, silicon, germanium, titanium dioxide, copper, silver and gold. In conclusion, spherical nano/micro particles can be prepared by using a pipe and gas flow. The mean diameter can be varied by controlling the gas flow velocity and can be estimated prior to the deposition by a calculation based on the inertial impaction theory.

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Abstract: This study investigates the controllable bi-stable behavior observed in laser ablation efficiency and surface roughness, manipulated by adjusting burst fluence and burst length. The presence of plasma shielding from the incoming laser radiation leads to a notable reduction in ablation efficiency, specifically for an even number of pulses within the burst. A toy model dedicated to ablation efficiency calculation taking into account the attenuation of incoming laser radiation by plasma generated from preceding pulses, yielding a mathematical recurrence relation, was introduced. This relation connects the ablation efficiency of consecutive pulses, thereby predicting bi-stability and sudden jumps in efficiency upon the number of pulses within the burst and variations in the burst laser fluence as control parameters. Modeling results employing this novel recurrence relation demonstrate both stable and bi-stable ablation efficiencies depending on burst fluence and burst length, having strong agreement with experimental observations.

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Abstract: The study delves into the critical aspect of spallation layer redeposition during ultrashort pulse ablation in liquid (LAL), a process wherein material ejected from the target due to spallation is partially redeposited back onto it. This phenomenon, predominantly observed in LAL, poses a significant limitation to the ablation efficiency by effectively reducing the net ablation volume. Through meticulously designed experiments employing pump-probe microscopy and ablation efficiency measurements for gold (Au) and an iron-nickel alloy (Fe0.5Ni0.5), the research not only experimentally corroborates the occurrence of spallation layer redeposition, previously predicted only by simulations but also quantifies its substantial impact. By manipulating the pulse duration and material properties to control stress confinement, the study unveils that a considerable portion, over 80%, of the ablated material is redeposited, thereby identifying spallation layer redeposition as a principal factor limiting LAL efficiency. These insights pave the way for devising novel strategies, such as modulating laser fluence or employing double-pulse techniques, aimed at mitigating redeposition to enhance the ablation efficiency and scalability of the LAL process.

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Abstract: Femtosecond laser-induced stress waves have many applications in various fields. Especially in the field of laser processing, the complex stress distribution of the stress waves is important. Although there have been many simulation studies of femtosecond laser-induced stress waves, few studies have experimentally measured the three-dimensional profiles. In this study, we measured the three-dimensional stress field of femtosecond laser-induced stress waves using a method that combines time-resolved Mach–Zehnder interferometry and time-resolved photoelasticity. Our newly proposed method allows the reconstruction of the three-dimensional axisymmetric dynamic stress field of the stress waves.

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Abstract: This study explores the use of pulsed laser ablation in liquids (PLAL) and pulsed laser deposition (PLD), for the fabrication of titanium and zinc oxide nanoparticles (NPs) and thin films, along with metal-doped variants. Varied laser parameters and deposition conditions were employed to tailor the properties of these materials. Extensive characterization was conducted to evaluate the influence of liquid environment, laser parameters, and deposition temperature on the morphology, size, crystallinity, and composition of the NPs and thin films. Results demonstrate the importance of dopants for enhancing the photoactivity of titanium and zinc oxide materials in degrading microplastics, as observed through photolysis experiments under solar lamp irradiation.

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Abstract: This study explores the broadband enhancement of laser-induced damage (LID) on silica optical flats induced by femtosecond laser pulses. The process generates surface nanostructures, specifically random pillars, leading to a significant increase in transmission across a wide spectral range. Testing the nanotextured silica surfaces for LID revealed notably higher laser-induced damage thresholds across most of the visible spectrum, surpassing those of the original substrates. Experimental observations demonstrated a broadband enhancement in laser-induced damage, particularly noticeable with single few-nanosecond laser pulses across three test wavelengths, indicating increased LID. These findings offer valuable insights into LID on nanostructured surfaces. This research holds potential implications for optics, telecommunications, and paves the way for the development of laser-induced materials processing with customizable optical resistance.

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Abstract: With two-color double pulse irradiation method, it was found that the uniform Laser Induced Periodic Surface Structure (LIPSS) was formed. In our previous study, to evaluate the uniformity of LIPSS, The Perpendicular Period and Phase Scanning (P3S) method was invented. P3S assesses the uniformity of LIPSS using the standard deviation of the peak period and the average of the phase difference in the direction perpendicular to LIPSS. However, the mechanism of uniform LIPSS formation was not understood. In this study, the purpose is to experimentally clarify the uniformity due to the combination of the polarization directions of the double pulses, and to elucidate the mechanism of the formation of uniformity LIPSS by comparing the results with a 3-D electromagnetic particle-in-cell simulation.

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Abstract: Ultrashort laser pulses are applied to thin metal films to induce the formation of diverse morphology nanostructures that depend on the pulse energy. The shape of the structure plays a crucial role in determining the optical properties, making control of the morphology pivotal. The formation of single-pulse gold structures is determined to be due to the thermoelastic stress and surface tension or capillary forces. The periodic arrangement of metallic nanostructures enables the excitation of hybridized plasmonic modes, resulting in the narrowing and enhancement of plasmon resonance. Since the structures are formed on the metal with plain film among them, the propagating surface polariton couples with surface lattice resonance, producing a dispersive and high-quality resonance. The formation of single-pulse-induced structures on 25, 50, 75, and 100 nm gold thicknesses using direct laser writing was investigated. The required pulse fluence was determined for each thickness to obtain the corresponding morphology – bumps, cones, or jets. The created theoretical model described the induced thermal effects. Additionally, the manipulation in shape by changing the grating period was in detail investigated. Reducing the distance between the structures modifies the morphology, providing an additional degree of freedom to control the shape. Finally, the plasmonic properties of these gratings were investigated. The resonant wavelength and quality are highly dependent on the morphology, and increasing the size of the structure results in a shift towards longer wavelengths.

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Abstract: Recent advances in 2PP technology have made it possible to use higher scanning speeds and lower processing times. Using higher scanning speeds creates new challenges, hence a thorough understanding of the material performance at this new processing window is essential. A comprehensive study of the polymerization threshold for fabrication speeds up to 600 mms−1 using a 63x and a 10x objective was carried out.

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Abstract: Laser-processing techniques offer innovative and versatile methods for the development of stimuli-responsive materials, which are essential in creating advanced functional devices, particularly aiming at sensor applications. This paper explores the role of laser-based methods, including Laser-Induced Forward Transfer (LIFT) and Matrix-Assisted Pulsed Laser Evaporation (MAPLE), in the precise deposition of materials for various applications. The ability to deposit nanocomposite materials using LIFT and MAPLE enables the development of gas sensors with high selectivity and sensitivity to pollutants, temperature, or humidity changes.

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Abstract: This study focuses on optimizing the fabrication of foam targets for laser-driven inertial fusion energy, using two-photon polymerization (2PP). Despite its nanoscale precision, 2PP faces challenges such as stitching errors in large prints, data limitations, and extended fabrication times. We investigate the impact of foam structure and printing parameters on the foam stability and fabrication time. In addition, the research identifies and addresses key limitations, paving the way for future optimizations.

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Abstract: We report the fine periodic nanostructure formation process on metal and semiconductor surfaces in air with few-cycle 7-fs laser pulses and its physical mechanism. The periodicity can be explained as arising from the excitation of short-range propagating surface plasmon polaritons, and the observed periods are in good agreement with the model calculation results. Poster preffered.

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Abstract: We present the laser-assisted fabrication of periodic nanostructures on Nickel sheets and their use as cathodes in alkaline electrolysis (Fig. 1). We found that it exhibits enhanced electrochemical values and 3.7 times larger hydrogen production efficiency in comparison to untreated Nickel sheets. In a second step, further electrodeposition of nickel particles was performed. The resulting electrodeposited-laser-nanostructured (ELN) electrode exhibited further increased hydrogen evolution reaction activity and further improved electrochemical characteristics. Scanning electron microscopy (SEM) revealed a dendrite-like morphology for the ELN electrode surface. Thus, the enhanced activity has been attributed to the concomitant enlargement of the electrode’s electrocatalytic area. The ELN electrode was measured to produce almost 5 times more hydrogen gas than a flat Ni electrode. Three dimensional electrodes have been also prepared using Pulsed Laser Deposition (PLD). Nickel foam has been used as the base material and Nickel layers have been successfully deposited with PLD. The laser-treated electrode exhibits enhanced electrochemical characteristics when compared to the untreated Ni foam. The above results demonstrate the application of lasers in the preparation of efficient Hydrogen-producing electrodes thus significantly contributing to the green energy transition and global environmental concerns.

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Abstract: Molybdenum disulfide (MoS2) is a typical 2D-material attracting in the last years great interest for photocatalysis, optoelectronic and sensing applications. In the field of the chemical sensing, semiconductor surface-enhanced Raman scattering (SERS) has attracted more and more attention due to the possibility to overcome some deficiencies of noble metal nanostructures. A key goal in the employ of semiconductors like 2D-MoS2 for SERS, is the improvement of the chemical mechanism (CM) of enhancement, mainly based on charge transfer phenomena. Recent progresses in the sensitivity were reported for defective MoS2 nanosheets and for complex architectures, like MoS2-nanoflowers [1, 2]. However, MoS2 layers can easily suffer from aggregation phenomena that negatively influence the CM of enhancement. In this respect, hierarchical MoS2-based nanostructures provide a hopeful approach to overcome the problem of the self- aggregation, as they are characterized by more stable structures with high chemical sensitivity. Here, MoS2 nanosheets were proper modified by laser beam irradiation in aqueous dispersion. This is an easy, green and contaminant-free approach able to induce significant structural modifications. Highly defective MoS2 layers and hierarchical architectures, like flower, tube and assembled lamellar structures, were obtained by a Nd:YAG nanosecond pulsed laser and were chemically characterised by XPS, UV and PL spectroscopies. The morphology of samples was assessed by scanning transmission electron and atomic force microscopy. SERS properties were studied using the 4-mercaptobenzoic acid (4-MBA) as a standard molecule. By using a Micro-Raman spectrometer, it was possible to find quickly isolated hierarchical structures and study the signal enhancement of the surface adsorbed analyte. Different chemical sensitivities were found as a function of the shape and composition and were attributed to different contributions: (a) the formation of a 1T MoS2 phase, (b) the high surface area of the produced structures and (c) the presence of laser-induced defects. The as-developed strategy may therefore open up interesting perspectives for designing semiconductor materials in the field of SERS sensing.

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Abstract: The study of photonic crystals (PhC), first proposed in 1987, remains a field of high interest given the wide number of possibilities to control and manipulate the flow of light in different ways, and mostly, given the recent advances on technologies and techniques that allow to realize and test these materials experimentally [1]. One of these techniques is two-photon lithography, which is a well-established Laser Direct Writing technique (LDW) used over the last decades for manufacturing high precision 3D micro and nanostructures [2], and which appears as a suitable and high desirable technique for the fabrication of 3D PhC. The goal of this study has been to fabricate a 3D PhC able to slow down the light propagation in the visible and near infrared range, and spatially separate its frequency components, leading to the so-called “Rainbow trapping” effect [3], which results in an increase of light intensity chromatically resolved along the crystal, and thus can be used for application in which enhanced light-matter interaction is required.

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Abstract: In this work, we report the use of Laser Induced Forward Transfer (LIFT) for the development of complex cell structures of tumor and LN cells in organ-on-chip devices, in order to study the metastatic behavior of cancer cells in lymphatic vessels. LIFT is employed as a 3D bioprinting technique, utilizing multilayer printing of 2D layers, rapidly immobilizing cells and extracellular matrices, for better imitation of the cancer tissue microenvironment. The design of the microfluidic chip includes culture chambers, as well as microchannels, so as to replicate blood and lymphatic flows. For chip fabrication, an LCD 3D printer is utilized in combination with a biocompatible, translucent resin.

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Abstract: Over the past two decades, Multi-Photon Lithography (MPL) has emerged as a highly effective manufacturing technique for crafting complicated three-dimensional (3D) microstructures with sub-microns resolved features.[1] MPL has played a pivotal role in advancing a diverse range of fields including micro-electronics,[2] micro-optics/photonics,[3] biomedicine,[4] microfluidics,[5] and plasmonic devices,[6] among others. In a typical MPL process, a photosensitive material, composed of reactive oligomers and a photoinitiator (PI), is exposed to high-intensity radiation by a tightly focused fs laser pulsed beam. Due to the high laser intensities, the nonlinear optical process of multi-photon absorption is manifested. Consequently, the PI absorbs simultaneously two or more photons through virtual intermediate states, leading to its decomposition into radicals. These radicals induce a cross-linking reaction of the oligomers. Unlike single-photon absorption, multi-photon processes enable the localization of photochemically induced polymerization to the focal point of incident laser beam, resulting in the precise printing of structures with feature sizes below the diffraction limit of light. The effectiveness of the PI is widely recognized to significantly influence various critical aspects of the printing process, such as the resolution and fabrication time of the 3D microstructures. So far, different synthetic approaches have been proposed to tune the efficiency of PIs, which is generally expressed by their two-photon absorption cross section σ. These approaches involve manipulating different structural parameters of PIs, as for instance, the size, the planarity, the aromatic properties of the monomeric units (e.g., through selective doping of the carbon framework with heteroatoms) and the kind of the peripheral functionalization (e.g., by incorporating electron donating and/or accepting substituents). From the aforementioned strategies, the most successful motif for molecules orientated towards MPL consists of electron donating and accepting functionalities, bridged by a π-conjugated spacer. In that view, significant efforts have been dedicated to synthesize compounds acting as strong electron donors/acceptors to enhance the performance of MPL. The present work assesses the efficiency of newly synthesized indane-1,3-dione-based push-pull dyes as PIs, comparing the findings with previously studied triphenylamine-based aldehydes and standard PIs for MPL applications. The present PIs exhibit strong nonlinear optical properties (i.e., two-photon absorption cross section and second-order hyperpolarizability) resulting in 3D structures with low fabrication threshold and high resolution. Most importantly, the fabricated structures display low fluorescence quantum yield. These findings render them highly promise for advancing applications in photonics, optoelectronics, medicine, and other innovative fields.

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Abstract: Ultrafast laser-induced surface texturing became a well-recognized technique of surface functionalization, with comparatively little work focused on the accompanying chemical changes. This paper reports a detailed investigation of the oxidation mechanisms induced on metals in the form of pure metal and metallic glass. Ultrafast laser irradiation was performed in ambient and high vacuum conditions on tungsten to generate so-called High Spatial Frequency Laser Induced Periodic Surface Structures (HSFL) with a sub- 100 nm period and sub-20 nm amplitude, as they are supposed to arise in a non-ablative regime. Scanning Transmission electron microscopy cross-sectional images, and x-ray photoelectron spectroscopy analyses reveal significant structural differences between the laser-generated oxides and the oxides accumulated over time from ambient exposure [1]. The oxidation mechanism during ultrafast laser interaction was examined with the help of Two Temperature Model and Molecular Dynamics simulations (TTM-MD) complemented by oxygen diffusion data, providing a predictive insight into the development of a thin oxide layer induced by the laser, a conclusion substantiated by the STEM images. This study is complemented by a detailed analysis of ultrafast laser irradiation of metallic glasses under conditions of generation in a one-step laser process of dense nanowell arrays with dimensions down to 20 nm spontaneously formed in the ultrafast laser irradiation spot [2]. In addition to the topographic functionalization, the laser-irradiated amorphous material exhibits structural changes analyzed by spectroscopic techniques at the nanoscale such as energy-dispersive X-ray spectroscopy and electron energy loss spectroscopy. Results reveal structural changes consisting of nanocrystals of monoclinic zirconia that grow within the amorphous ZrCu matrix. The mechanism is highlighted by an atomistic simulation of the laser-induced nanowell formation.

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Abstract: We propose a novel approach to control the shape of a broadband THz beam and the energy redistribution within the beam profile by direct manipulation of the THz emitter.

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Abstract: The study reevaluates the phenomenon of incubation in ultra-short pulse laser ablation, challenging the traditional understanding that primarily associates incubation with global material alterations. By focusing on the local field effects, particularly at crater edges, the research uncovers a more complex picture of incubation, where local enhancements play a significant role. Through a series of experiments and simulations on aluminum and stainless steel AISI 304, the research demonstrates that local field enhancements can lead to selective ablation and the formation of Laser-Induced Periodic Surface Structures, indicating a departure from uniform incubation processes. These findings suggest a need to consider both local and global effects to fully understand the dynamics of ultra-short pulse laser ablation, particularly for applications in precision material processing.

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Abstract: The laser-induced plasma-assisted ablation (LIPAA) achieves high-quality surface microfabrication of transparent materials [1]. In the LIPAA process, strong interactions between laser light and plasma results in ablation and selective metallization on the rear side of the transparent substrate in micrometer scale. We focused on the metal thin films deposited on the transparent substrate during LIPAA process and explored the possibility of transferring the laser-induced periodic surface structures (LIPSS) on the substrate. In this presentation, we investigated the fabrication characteristics of LIPSS on a glass by the LIPAA process using a nanosecond laser.

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Abstract: Carbon fiber reinforced polymer (CFRP) is widely used in aerial platform confinement of high-power continuous laser facilities due to its lightweight and high stiffness. In the high-power laser system, abundant random stray light is inevitably generated due to the surface scattering and the residual reflection, which may cause damage to the high-reflection film optical components. Thus, to realize the clean environment control in a high-power continuous laser system from the root, the degradation of high reflection film performance induced by contaminants induced by stray light irradiation of CFRP materials was studied. The damage threshold of a typical resin-based carbon fiber composite was investigated under continuous laser irradiation (λ=1064 nm). The results showed that the surface temperature rise effect of CFRP increased significantly with the increase of laser spot size at the same power, and the laser-induced damage threshold of CFRP decreased significantly. When the laser spot diameter is 8.4 mm, the damage threshold of CFRP after 30 s continuous laser irradiation is 14.07 W/cm2. The stray light energy in high energy continuous laser system is generally less than one thousandth of the main laser energy (kilowatt level). The stray light energy (1.44 W/cm2) far below the damage threshold of CFRP was adopted for irradiation experiment. After the highly reflective film optical components and CFRP were placed in the same sealed chamber for a week, the surface temperature rise effect was significantly increased under 3 kW laser irradiation. About 2°C can increase the maximum temperature, and the film layer ablative defects were accompanied, which was unacceptable for continuous laser systems with tens of millions of energies or higher. Thus, it is necessary to seriously consider the influence of stray light irradiation CFRP on the high reflection film optical component contamination damage in high-power continuous laser facilities.

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Abstract: Ultra-short pulse laser bursts have attracted a lot of attention in industrial micromachining due to their advantages over conventional laser modes, especially their high ablation efficiency. In burst mode, a packet of multiple pulses with the same total energy replaces the single pulse with the energy Ep. The main feature is the intra-burst repetition rate within the burst, which is higher than the (inter-) pulse repetition rate of conventional single pulses. Burst-mode lasers usually operate at different repetition rates, either in the MHz or GHz range, with intra-pulse delays in the nanosecond or picosecond range, respectively. The high intra-pulse repetition rates lead to strong heat accumulation, which in turn promotes ablation efficiency. This high ablation efficiency, which cannot be achieved in conventional single-pulse mode, offers considerable advantages in material processing. Since Kerse et. al [1] introduced ablative cooling, many research groups have investigated the use of GHz bursting in metal processing [3-4]. However, relatively little attention has been paid to the less expensive and more accessible MHz burst mode. This motivates us to investigate the ablation efficiency of the MHz burst mode for industrial applications. In this contribution, we investigate the possibility of using MHz burst lasers (wavelength 1030 and 343 nm, intra-burst repetition rate 40 MHz, and inter-pulse repetition rate 333 kHz) to achieve similar advantages to GHz burst lasers in the processing of metal foils. Our experimental focus is on measuring ablation efficiency as the material removed per fluence (∆d/F = h/ft/F), calculated from the foil thickness (h), repetition rate (f), and time to drill through (t). The peak fluence is F = 2Ep/(w0), where Ep is the pulse energy and w0 is the beam waist radius. We investigated the ablation efficiency of the MHz burst mode by varying the parameters including the laser wavelength (1030 nm or 343 nm), the material of the foils (SS, Al, Ti, and Cu) with different thicknesses (25µm, 50µm, and 75µm), the pulse durations (300fs - 10ps) and the number of pulses in the bursts (1-43). In addition, the results obtained are compared with those obtained with ns pulses at pulse durations corresponding to the total burst durations. Our results show the potential of MHz bursts as a viable and cost-effective alternative to GHz bursts for wider use in industrial applications such as laser drilling and micromachining.

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Abstract: Silicon carbide (SiC) is a third-generation semiconductor material and known for its high-temperature resistance and wide bandgap characteristics. However, the poses challenges of SiC process was the inherent hardness, and it makes traditional grinding and polishing time-consuming and resource-intensive, then significantly elevating wafer production costs. Laser systems can be applied for material marking, drilling, cutting, and surface modification. In previous studies, several research presented that the femtosecond [1-2] and nanosecond [3] laser system was employed to ablate and polish the SiC surface, wherein the influence on surface roughness, ablation depth and oxidation of SiC have been computed. Therein, the laser parameters such as pulse energy, spot overlapping and defocus of laser spot were investigated. Furthermore, some studies discuss effect of the laser ablation and polishing for the following chemical-mechanical polishing (CMP) [4-5] process. It is noteworthy that the majority of these studies employed femtosecond laser systems, but the system price of femtosecond laser was too high to be widely applied in the SiC manufacturing facilities. Therefore, the suitable laser treatment mechanism on SiC substrates was investigated in this manuscript, and the parameters such as the scanning speed, pulse repetition frequency, laser path and repetition times of laser system can be adjusted to find the suitable values for soften the hardness of SiC substrates. In this study, the ultraviolet laser system was employed to modify the characteristics of SiC surface. We investigated the effects of different processing path, speeds, frequencies, and power levels on modification depth, oxidation, and hardness changes in the SiC surface. By inducing the surface softening, the goal is to enhance the efficiency of subsequent CMP process. Preliminary test results indicated that laser treatment of SiC surfaces leads to the formation of oxides, causing the surface hardness to reduce to approximately 30% of the original value. This reduction facilitates subsequent CMP processes, accelerating material removal rates and minimizing tool wear. The development presented in this research has the potential to increase SiC wafer productivity and reduce production costs.

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Abstract: Here, we present our findings on Ag nanowires plasmonic welding using a femtosecond supercontinuum pulsed laser with selected wavelength varied between UV-B and visible spectral range. As a result, this treatment increases nanowires contact area, reducing sheet resistance of the nanowires grid, while maintaining its high transmittance. Here, we will demonstrate TCEs based on optically welded silver nanowires, which exhibit both high transmittance of T > 85% and low sheet resistance Rs < 20 Ω/sq. Using conventional ITO and Al:ZnO (AZO) TCEs as our benchmarks, we will compare their electrical and transmittance performance to optically-welded Ag nanowires grid, and ZnO/AgNWs/ZnO hybrid electrodes

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Abstract: We focused on pulsed laser deposition (PLD) as a new low-k film formation process, in which nanoparticles can be deposited to form nanoporous films. Theoretical calculations suggest that the smaller the nanoparticle size, the lower the dielectric constant owing to the quantum confinement effect. Therefore,we believe that ultra-low dielectric constant films can be formed by depositing smaller nanoparticles. We deposited nanoparticles by PLD using three combinations of lasers and materials and investigated the size of the deposited nanoparticles.The combinations are (a) F2 laser and SiO2, (b) ArF excimer laser and SiO2, and (c) ArF excimer laser.The ablation process in each combination was categorized as thermal or non-thermal ablation, and it was found that smaller particles were deposited in the non-thermal ablation combination.We calculated the Gibbs free energy of the nanoparticles and determined the critical particle size that separates the growth and decay of the particles in the thermal equilibrium process.The results showed that in the case of non-thermal ablation, the deposited particles were smaller than the critical particle size.

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Abstract: In recent years, there has been a significant surge in advancements in thin film technology aimed at fostering clean and renewable energy sources. However, a critical challenge that persists is the upscaling of manufacturing processes, thus a paradigm shift in the industrialization of certain technologies occurred focused on the automation of the process. Among the myriad of technological solutions, Pulsed Laser Deposition (PLD) stands out as an exceptionally versatile tool for producing a wide range of nanoscale materials with precisely controllable properties. Our research group has demonstrated in recent years that in-situ monitoring of the PLD process is crucial for establishing correlations between plasma behaviour and thin film characteristics, thus paving the way for process automation. In this study, we apply this approach to gain insights into the formation of oxynitride films. Beginning with a bottom-up approach, we characterize the deposition process of selected oxides and oxynitrides (such as TiOxNy, ZrOxNy, and HfOxNy) with the objective of elucidating plasma-thin film relationships to facilitate the upscaling of PLD technology. Our investigations employed angle and time-resolved Langmuir probe techniques coupled with real-time optical emission spectroscopy to scrutinize the deposition process. We identified distinct signatures in the charge particle density distribution for gas-phase oxidation processes involving metallic species. Time-resolved analysis unveiled the intricate dynamics of a two-temperature plasma with distinctive angular structuring. To account for the peculiarities of PLD, both on-axis and off-axis deposition geometries were employed to examine the influence of charge kinetic energy on defect and oxynitride phase formation. Subsequently, the deposited films underwent comprehensive characterization using Atomic Force Microscopy (AFM), Scanning Electron Microscopy (SEM), X-ray Diffraction (XRD), X-ray Photoelectron Spectroscopy (XPS), and electrical measurements. Finally, we established correlations between plasma properties during deposition and selected physical properties of the film, thereby identifying optimal conditions for the development of tailored oxynitride coatings

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Abstract: Laser-induced crystallization is a novel alternative to classical methods for crystallizing organic molecules but requires judicious choice of experimental parameters for the onset of crystallization to be predictable. This study investigated the impact of the laser repetition rate on the time delay from the start of the pulsed laser illumination to the initiation of crystallization, the so-called induction time. A supersaturated urea solution was irradiated with near-infrared laser pulses with an intensity of 1E14 W/cm2 while varying the repetition rate from 10 to 20 000 Hz. The optimal rate discovered ranged from 500 Hz to 1 kHz, quantified by the measured induction time (median 2-5 seconds) and the mean probability of inducing a successful crystallization event (5E−2 %). For higher repetition rates (5 kHz to 20 kHz), the mean probability dropped to 3E−3 %. The reduced efficiency at high repetition rates is likely due to an interaction between an existing thermocavitation bubble and subsequent pulses. These results suggest that an optimized pulse repetition rate can be a means to gain further control over the laser-induced crystallization process.

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Abstract: The optical properties of negatively charged nitrogen-vacancy (NV-) centers in diamond have garnered significant attention due to their potential applications in biology, medicine, quantum sensing and quantum information processing. In most cases, visible to near-infrared luminescence is recorded, upon the green laser excitation, and carries information on the NV spin which, in turn, may be manipulated using microwave fields. Although there is some research on nonlinear optical effects in bulk diamond and nanodiamonds, the impact of NV centers on such phenomena is far from being fully understood. Here, we investigate the influence of NV centers in high-quality crystalline diamonds (DNV-B1, B14, and electronic grade; Element Six / Thorlabs) on nonlinear optical effects using 230-fs-long laser pulses with a wavelength of 1030 nm and a repetition rate of 1 kHz. In particular, the optical Kerr effect (OKE) and multi-photon absorption were explored using the Z-scan technique. Our findings reveal that diamonds with NV centers generally exhibit a lower non-linear refractive index compared to pure diamond. However, unlike pure diamond, the NV-diamonds exhibit very strong nonlinear absorption effects, attributed to its bandgap energy level structure. As the energy of the laser pulse increases, we observe two-photon absorption (TPA) initially, followed by saturated absorption (SA), and finally reversed saturated absorption (RSA). These effects are also strongly enhanced with increasing NV concentration. To identify the underlying processes, fluorescence (FL) spectra excited by laser pulses of various energies were examined. These spectra consist of a zero-phonon line (ZPL) of NV0 observed at 575 nm and a broad band centered around 640 nm, which are associated with electron transitions between excited and ground states of NV0. The lack of NV- ZPL at 637 nm, a prominent feature under green light illumination, indicates the conversion of NV- to NV0 caused by multiphoton ionization. The spectrally integrated FL follows a quadratic dependence on laser pulse energy indicating the involvement of two-photon processes in the excitation of the FL spectra. In summary, our studies unveil intriguing optical nonlinearity in diamonds with NV concentrations of a few ppm, which holds significant interest for researchers in the field of quantum sensing. Figure: (from left to right) Bandgap energy level structure of NV-doped diamond. The normalized open-aperture (OA) and closed-aperture (CA) Z-scan signals recorded for laser pulse energies varying from 500 nJ to 9 µJ. Fluorescence spectra excited with laser pulses of different energies.

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Abstract: Charge transport anisotropic dynamics within two-photon absorption (TPA) induced by ultrashort laser pulses in a Zinc Telluide (ZnTe) semiconductor crystal is detected and analyzed by using terahertz (THz) pulses. The anisotropy consists in an oscillation of the induced carrier density with crystal orientation. Electron densities as low as 〖10〗^13 〖cm〗^(-3) are detected, due to the high coupling of THz electric field with free carriers. The anisotropy of TPA and its dynamics are analyzed in samples with smooth surfaces first and then with surfaces pre-structured with LIPSS (Laser Induced Periodic Surface Structures). We show that pre-structuring the crystal surfaces clearly influences the intrinsic TPA-induced anisotropy.

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Abstract: Laser-induced breakdown spectroscopy (LIBS) is one of the simple elemental analysis method using laser-ablation sampling [1]. In typical LIBS analysis, the sample preparation can be simply done without acid digestion and dilution process and thus allows a rapid analysis of multiple elements. In this study, we conducted elemental discrimination of soybean paste according to its geographical origin using LIBS. Soybean paste is a seasoning widely used in East Asian countries. It is characterized by its high protein and amino acid content, excellent storage stability, and distinctive flavor and aroma, making it widely favored in culinary practices. In South Korea, numerous food companies distribute soybean paste products, with a significant portion being produced in China. Distinguishing the origin of soybean paste is crucial for food distribution management. A total of 167 soybean paste samples were used in this study, with 101 being domestically produced and 66 from China. LIBS equipment measurements revealed the presence of elements such as C, Mg, Na, K, H, Ca, Cl, and P in soybean paste samples. The discrimination capabilities of the emission lines of these elements were investigated by using the concept of interclass distance. To evaluate the interclass distance, the difference between average of specific emission intensities measured for Chinese and Korean soybean paste samples was taken first and scaled by the common pooled standard deviation. The emission lines of Mg, P, and C showed relatively larger interclass distances (> 0.5). Thus, the three emission line intensities were considered in the k-NN modeling. Also, the classification performances of three 1-variable, three 2-variable, and one 3-variable models were evaluated following the leave-one-out validation process. Among the possible combinations of variables, the usage of both Mg and C emission intensities provided the best model. The highest classification accuracy (86.2%) was achieved by the Mg-C model at k = 13. Our research suggests that the classification methodology combining LIBS and k-NN can be an effective and practical choice for screening particular soybean paste products.

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Abstract: Viruses and bacteria spread rapidly through saliva or droplets, and their prolonged viability poses a serious threat to human health, especially during the COVID-19 epidemic. Therefore, the inhibition of virus or bacteria activity play an important role in surface treatment technology. Traditionally, virus inhibition involves chemical substance spraying or physical methods such as heat or ultraviolet light, all of which potentially harm the respiratory system, eyes, or skin oh human body. The other virus inhibition method was also presented such as electrical stimulation [1], acoustics, plasma, and microwaves. In addition, the metal surface such as cooper surface can destroy the ester and protein surrounding virus [2]. Thus, we used the copper surface and given a variable-frequency electrical stimulation for the virus and bacterial [3]. The results showed that the activity of coronavirus 229E can be significantly inhibited under direct-current pulse stimulation with 25 mA current and specific frequency. The laser system can directly fabricate the electrode and pattern on flexible materials, and it had excellent opto-electrical properties [4]. The previous research [5] presented that the electrical field emission properties can be enhanced by surface structing of copper film fabricated by laser system. Therefore, we integrate the micropattern induced by laser system and electrical stimulation on conductive materials to investigate the inhibition effect of viral activity. Micropatterns are created on conductive films using by ultraviolet laser system, which can enhance the effectiveness of electrical stimulation in inhibiting of virus activity. The conductive films include copper film that originally had good viral inhibition effect and ITO film that have excellent optical transparent effect. In addition, the micropattern with circle and rectangle shapes, and different dimension and spacing ranged from 50 to 200 μm were designed. By utilizing variable-frequency electrical stimulation, we explore the inhibition rates of 229E coronavirus under different dimensions, spacings, and shapes of micropatterns, aiming to achieve an inhibition rate of over 90%. Through the fabrication of micropatterns on the surface of conductive substrates, the sharp electric field effect can be enhanced and even reducing the time and power consumption required for electrical stimulation in viral activity inhibition. This advancement significantly broadens the application scope, efficiently reducing virus activity and providing substantial assistance to public health.

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Abstract: Here, we will present our findings on high-precision CIGS solar cell processing P1, P2, and P3 using femtosecond (<100 fs) supercontinuum pulsed laser with a tunable UV wavelength. Femtosecond pulses enable highly localized heating due to a time scale shorter than the electron–phonon equilibrium time. This may offer a low heat-affected zone and prevent undesirable melting of CIGS, which causes phase transition and creates conductive channels [3], which cause shortcuts and reduce overall PV module performance. By using femtosecond laser operating at UV wavelength above the bandgap of Al:ZnO we can enable highly controlled P3 scribing due to strong absorption in all the layers. The dependence of ablation depth on laser fluence and overlap ratio will be experimentally studied, with discussions on the corresponding ablation mechanisms.

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Abstract: Melanin is an endogenous granular pigment that can present colors ranging from yellow to black and is produced by melanocytes present in the basal layer of the oral epithelium. Changes or disorders related to melanin and other pigments can be initiated by trauma, infection, habits (smoking, food), use of medications (antimalarials, minocyclines) and by some systemic factors such as Addison's disease, Peutz-Jeghers syndrome and tumors. Physiological gingival melanin pigmentation (GMP), also called racial melanosis, is a non-pathological condition with variable prevalence in different ethnic groups. There are only a few reports in the literature [1] comparing the effects of lasers on GMP. This study was performed to compare and evaluate the effects of the Nd:YAG laser, CO2 laser at superpulse mode, and conventional surgery with Kirland scalpel applied for gingival depigmentation. Recently, several surgical techniques for gingival depigmentation have been proposed with the aim of removing physiological pigmented lesions from the gingival tissue. However, the decision and indication for its removal must be based mainly on a correct diagnosis of physiological pigmentation, determining differential diagnoses with other changes that can also manifest pigmented lesions in the oral cavity. After confirming the diagnosis of racial melanosis, the objective of this work was to present a clinical case in which we used different ablative forms of treatment using CO2 and Nd YAG lasers in the same patient. The removal of pigmented lesions in the oral mucosa was divided as follows: Upper right quadrant: CO 2 laser, upper left quadrant: Kirkland scalpel (conventional technique), lower region of the oral epithelium: Nd YAG. This division aimed to compare the results of the conventional surgical technique with ablative techniques. Ablation of the hyperpigmented gingiva with CO2 and ND:YAG laser was accomplished with minimal carbonization and almost no bleeding. Postoperative healing was uneventful, with no significant postoperative pain. Partial repigmentation was observed only in non-ablated areas, so additional treatment was performed in these regions regardless of the laser used. In conclusion, we have that the application of the superpulse mode of the CO2 laser or the Nd:YAG laser appears to be an effective and safe method for eliminating (GMP,) as it causes less bleeding, consequently less edema and less postoperative pain when compared to the conventional surgical method

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Abstract: The ongoing progress in ultrafast laser technology has given a great impetus to material processing, enabling the realization of new photonic devices, with functionalities intimately related to the structuring scale. Here we propose an innovative approach based on the real-time probing of the activation of vibrational phonons as direct proof of molecular dynamics: monitoring the matrix evolution through the dynamics of anharmonic vibrational modes upon nonlinear excitation. The experimental investigations were conducted on amorphous silica, tracking the Si-O-Si antisymmetric stretching overtone located at 4415 nm. Upon nonlinear excitation, the rapid evolution of the molecular potential and the phonon population will be reflected in the absorption of the vibrational feature in the mid-infrared (MIR), such as inhomogeneous broadening and spectral shift. Our results emphasize the potential of this method, which can be easily extended to other local markers of vibrational coupling within the host glass structure.

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Abstract: Single crystal of aluminum nitride (AlN) has a high thermal conductivity and is an electrical insulator, and is great candidate material for UV-LED, UV-LD, power convertor, RF-HEMT and so on. In this research, we suggest the selective laser assisted chemical etching of aluminum nitride for high resolution material processing. The result is indicated that the processing from c-axis side is appeared a hexagonal shape and the sharpness is high. Also, as a parameter of laser output power and scanning speed, it is possible to control the size of the hexagonal shape.

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Abstract: The mechanism of colloidal alloy nanoparticle (NP) formation by laser ablation in liquids (LAL) has been intensively studied e.g. for fully miscible alloy systems like AgAu forming solid solution[1], partially miscible systems like FeAu with trends for segregation and core-shell structure formation[2], and immiscible elements (CuAg), where segregation was observable even in the ablation plume during early stage formation[3]. Recently, this approach has been successfully transferred to multi-component high entropy alloy (HEA) systems, where crystalline solid solution NPs of CrMnFeCoNi were generated by ps-LAL in ethanol[4] and amorphous structures were found after ns-LAL in acetonitrile[5]. However, to what extent the composition and crystal structure of laser-synthesized HEA-NP is affected by target composition, pulse duration, and the solvent is underexplored. In this work, we investigate how crystal structures, particle diameter distribution, and elemental composition of CrMnFeCoNi and CuPdAgPtAu HEA NPs are affected by laser pulse duration (ps vs. ns) and solvent type (ethanol, acetone), and in particular whether and to what extent the excess of one element in the HEA base target leads to elemental segregation in the HEA-NPs. Particle characterization was conducted by TEM/EDX as well as XRD. Preliminary studies showed a high phase stability of the solid solution fcc structure of the HEA-NPs at the excess of specifically chosen elements (Cr, Mn, Ag, Cu, Pt) though individual NPs, particularly in the Mn-rich CrMnFeCoNi samples, displayed segregation due to oxide phase formation. Interestingly, CuPdAgPtAu HEA-NPs displayed two solid solution NP fractions divided into Ag-rich and Pt-rich individual particles of comparable particle diameters. These de-mixing tendencies could be a hint towards particles formed at different cooling rates and could offer interesting insights into the HEA-NP formation mechanism by LAL under thermodynamic and kinetic control.

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Abstract: This study investigates the use of femtosecond (fs) laser pulses to create nitrogen-vacancy (NV) centers in diamond and fabricate microresonators, by two-photons polymerization, with embedded nanodiamonds for photonics and quantum sensing applications. The results demonstrate the potential of fs-laser techniques for engineering diamond-based devices with applications in photonics and quantum information technologies.

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Abstract: Titanium alloy and zirconia ceramics (3Y-TZP) are commonly used for medical implants because of their high-mechanical property and biocompatibility. We have observed fs-laser-induced periodic surface structure (LIPSS) on 3Y-TZP and confirmed positive effects on medical implant. To investigate the mechanism of LIPSS formation, we have carried out one-color double-pulse irradiation experiments. In this study, we report two-color double-pulse irradiation[4] on titanium alloy and 3Y-TZP with controlling polarization.

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Abstract: Laser processing of soda-lime glass, typically used as a cover in photovoltaic (PV) modules, to enhance mainly its optical, wetting and anti-soiling properties, is of significant importance for the PV industry. However, laser processing of a transparent, brittle and heat-sensitive material, such as glass, is challenging. Throughput and cost are still key issues and further improvements must be done to establish laser-glass processing as the standard processing method for PV module glass. Owing to the possibility of exploiting nonlinear light-matter interactions, the use of ultrashort pulsed lasers (USP) for laser-glass processing has already been proposed, offering excellent quality, when compared to any other conventional or laser processing technology. Nevertheless, the throughput of USP laser processing is still low in comparison to other laser technologies, such as nanosecond lasers. In this work, surface modification threshold experiments reveal ≈ 20 % increase in the ablation efficiency of soda-lime glass when heated from 20 °C to 200 °C. This stimulates currently conducted research to understand the temperature dependent absorption mechanism behind this effect, which can prove instrumental in increasing the throughput of USP laser processing. Motivated by this result, we use the Z-scan technique to determine the nonlinear optical properties of soda-lime glass. A fully automated Z-scan setup is designed and built to be capable of measuring over a wavelength range from 310 nm to 2600 nm with adjustable substrate temperatures from 20 °C to 1500°C. As an optical source, we use an Yb-doped regenerative amplifier, with an average power of 6 W, pulse duration of 180 fs and a central wavelength of 1030 nm. We calculate the four-photon absorption coefficient and nonlinear refractive index for soda-lime glass at room temperature and at 1030 nm. To the best of our knowledge, this is the first time that the four-photon absorption coefficient of soda-lime glass has been reported in the scientific literature.

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Abstract: High crystalline hydroxyapatite coating layer was fabricated by a droplet elimination pulsed-laser deposition scheme. Adhesion of this coating layer becomes stronger as increasing the annealing temperature. This coating will survive long period in vivo and enhance the bone-formation on its surface and strong and early bone-bonding will be obtained.

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Abstract: In this work, we investigate the laser-induced periodic surface structures (LIPSS) formation on soda-lime glass using a femtosecond (fs) laser source, with two different wavelengths are λ= 1030 nm and λ= 515 nm. Due to the nonlinear absorption behavior of the fs-laser beam in soda-lime glass, we introduce a framework featuring a combined thin metal film of silver and chromium (Ag:100 nm + Cr:30 nm) deposited onto soda-lime glass by DC sputtering, taht helps to absorb the laser beem on the material surface. This substrate is employed under green and IR light irradiations to induce the formation of LIPSS. Four different repetition rates (f) such as 10 kHz, 50 kHz, 100 kHz, and 250 kHz were employed.

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Abstract: The use of lasers in the life sciences has increased dramatically in recent years, most notably in the field of bioprinting, an additive manufacturing technique that makes it possible to precisely create living tissue. A laser-based bioprinting technique called Laser Induced Forward Transfer, can print cells in a wide variety of substrates, creating ex vivo grafts in terms of regenerative medicine. Different cell-laden bioinks combined with biomaterials were printed using a Nd:YAG laser operating at 532 nm. Specifically, in this study, the transfer dynamics between the laser and the biomaterials are examined with the use of a high-resolution camera to observe the printing phenomenon. Later, by adapting the laser parameters, cells are immobilized inside hydrogel in a controlled depth, exceeding 3 mm.

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Abstract: Pulsed laser ablation of multicomponent targets proceeds often incongruently resulting in changes in the target stoichiometry. However, the role of incongruent ablation in various laser applications remains virtually unexplored. Here we present mass spectrometric and theoretical studies on incongruent laser evaporation and its manifestations in the laser ablation plume. Particular attention is given to the delayed evaporation of a more volatile component under multi-shot ablation.

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Abstract: In today's fast-evolving landscape of portable electronics, wearable tech, LEDs, microelectronics, and bioelectronics, creating metallic circuits on polymer substrates with strong adhesion properties poses a growing challenge. This study successfully fabricated high-resolution metallic circuits on commercial polymer surfaces (CE221 and ULTEM 9085) using laser direct structuring (LDS) with copper acetylacetonate Cu(acac)2. The selective metallization mechanism was systematically explored, with RAMAN Spectroscopy confirming the formation of Cu0 (elemental copper) via photochemical reduction reaction after 1032 nm NIR pulsed laser irradiation. Detailed analysis delved into laser activation and subsequent copper plating mechanisms, along with measuring electrical resistance and surface adhesion of the copper tracks on the polymer. Furthermore, the technology's potential was exemplified through a 555 timer flasher demonstration, showcasing how this process can provide the necessary electrical, mechanical, and thermal properties for future real-world applications in 3D printed electronics.

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Abstract: Silver (I) oxide and silver (I, III) oxide were formed by machining bulk silver with an ultrafast laser. The machined sample was studied via Raman spectroscopy. Laser machining parameters have an effect on the type and amount of silver oxide created.

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Abstract: This talk will highlight the application of laser ablation and sintering in disrupting the printed electronics industry. It presents a dry multilateral printing approach that enables the printing of various pure materials and devices ranging from metals and semiconductors to insulators and nanocomposites.

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Abstract: We present the results of laser-induced crystallization of semiconductor nanomaterials and discuss its physical mechanism based on laser-generated stress wave and ultrafast melting

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Abstract: In the presented study we report on the successful micromachining of highly porous transport layers, which are subject of further investigations with the ultimate aim for improvements in the efficiency of electrolysis stacks used for hydrogen production. Different strategies, such as ultrashort laser pulses, inter-burst modes and multi-beam generation via spatial light modulation are combined for optimal processing results. As a speciality, the ablation process is conducted within a liquid environment in order to achieve highest dimensional accuracy of the laser drilled holes and maximize the achievable porousity trough elevated heat conduction.

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Abstract: Carbon complexes, such as layered graphite, porous graphite, and monolithic carbon aerogels, possess unique material properties distinctive of their structure, and have been applied towards a wide range of applications. Laser-induced graphitization is a direct write technique which offers the simultaneous synthesis and patterning of carbon complexes by simply scanning a laser beam over a polymeric precursor. By simply scanning the laser beam in three dimensions such materials can be rapidly structured into desired architectures, offering the laser direct writing (LDW) of various key applications, including sensors, unique identification tags, and energy devices. Despite the versatility and scalability of this technique, a deeper understanding of the underlying photothermal mechanisms is required to exquisitely control the resulting morphology and properties. The specific formation mechanism of the carbon complexes has been an issue of debate for many years with the prevailing notion of a simple photothermal conversion reaction that mainly depends on the laser fluence. In this study, we reveal that structural formation is a highly complex, temporally- and spatially-dependent phenomena which cannot be explained solely by the laser fluence, and further propose and validate a mechanism based on the formation of laser-induced defects. Our proposed formation mechanism is composed of 3 phases, (1) nucleation of laser-induced defects, (2) slow growth of defects and increase in defect number, and (3) the sudden growth of defects due to graphitization. The model is further validated by intentionally introducing controlled defects by femtosecond laser irradiation, and indicate the implications of a two-laser laser direct writing technique to go beyond the current processing limits.

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Abstract: While 3D-networks of nano-textured carbon fibers (CFs) are highly promising materials for electrochemical energy storage and tissue engineering applications, it is extremely difficult to perform wide-area nano-texturing using conventional methods without damaging the bulk structure. Therefore, nano-texturing is generally performed on delicate fibers by chemical processing, which relies on the use of highly toxic chemicals that are environmentally unfriendly and may cause unexpected reactions upon application (i.e., explosions for energy storage or cell-death for tissue engineering) unless carefully cleaned. Here, we demonstrate the fabrication of an interconnected 3D network of CFs possessing periodic nano-scaled ripples, or laser-induced periodic surface structures (LIPSS) via femtosecond (fs) laser processing [1]. For the fs-laser-processed CFs, we observed the coexistence of two distinct types of LIPSS with different spatial periodicities of ~800 nm (low-spatial-frequency LIPSS, LSFL) and ~100 nm (high-spatial-frequency LIPSS, HSFL). Furthermore, it was indicated that the orientation of the LSFL was highly dependent on the structural-morphology and propagation direction of the fibers, while the orientation of the HSFL was solely dependent on the fundamental laser polarization direction. This suggests that the two LIPSS formed through different interference mechanisms; specifically, LSFL formed through the interference with Fresnel diffraction patterns projected by the fiber edges, while HSFL formed through the interference of surface plasmons leading to LSFL-splitting. The current findings not only open a new route for the preparation of nano-textured carbon materials for future energy and regenerative-medicine applications, but also reveals important fundamental insights into the underlining physical phenomena of LIPSS. Figure

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Abstract: We applied microstructures to stainless steel surfaces and investigated parameter windows for laser induced periodic surface structures (LIPSS) and cone like protrusions (CLPs). Furthermore, we present a setup to proove the low reflectance of such surfaces.

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Abstract: Our primary objective is to share the endeavors undertaken within the laser-matter interaction community concerning the application of laser sintering as an additive manufacturing tool. The potential of this technique has been thoroughly explored across various domains such as Food Industry, Energy sector, Automotive packaging, and Space exploration. Direct laser sintering facilitates the mass production of digital conductive and dielectric patterns. This innovative approach offers substantial benefits to existing additive manufacturing technologies, resulting in products characterized by reduced resistivities, enhanced adhesion, high aspect ratios, and high-resolution line patterns on flexible and temperature-sensitive substrates. The development of transformative, cost-effective technologies has been a central focus, aiming higher aspect ratios and finer patterning, in alignment with the prevailing trend towards sustainability and environmental stewardship. Illustrative examples of laser sintering applications within the energy sector, such as the fabrication of photovoltaic grid electrodes, will be presented. Additionally, insights will be provided into the utilization of this additive manufacturing method, alongside adaptive laser ablation and drilling, in the production of advanced compact automotive sensor packages for autonomous vehicles. Our efforts have been dedicated to the meticulous design and optimization of fabrication processes, achieving impressive speeds of up to thousands mm/sec, with the objective of seamless integration into a pilot line. The Food industry, encompassing crucial activities such as resourcing, production, processing, packaging, and marketing of edible goods, represents a cornerstone of the global economy. As global initiatives towards ensuring food safety and security gain momentum, there is a heightened interest in smart, "active" food packaging technologies. A notable highlight of our presentation will be the development of intelligent food packaging CO2 sensors capable of monitoring gas released during food shelf life, achieved through precise localized laser sintering techniques. Furthermore, international endeavors are focused on in-situ resource utilization (ISRU), aimed at minimizing costs associated with lunar and Martian missions. The utilization of indigenous space materials for fabricating objects, components, building blocks, or platforms utilizing additive manufacturing techniques assumes paramount significance. Preliminary findings in the laser sintering of regolith will be discussed in this context.

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Abstract: An increasing number of novel synthesized materials allows extensive studies for their use in additive manufacturing, especially offered by diverse optical 3D printing techniques. The structuring via laser multiphoton 3D lithography empowers miniaturization and integration for various applications. However, there is still a limited number of reports on the precise structurization of polycrystalline and transparent YAG (Y3Al5O12). Research discussed in this study experimentally proves the possibility to synthesize and 3D micro-structure pure, crystalline, and transparent YAG substances which are opening micro-/nano-engineering of optically active devices such as micro-lasers and photonic integrated circuits (PICs). XRD patterns have shown that pure YAG is only obtained when samples were heated at 1600°C, since when heated at 600°C no crystallized YAG is formed and when heated at 1500°C some impurities remain. Structurization study of the material was performed while shifting laser irradiation power on X-axis from 50 mW to 250 mW and translation speed on Y-axis from 5000 µm/s to 10000 µm/s, with size of each formed woodpile 3D structure being sized 50 µm x 50 µm x 30 µm. After structurization samples were rinsed in ethanol and Novec™ 7100 for contrasting. SEM images of sample obtained without heating showed that most of the fabricated structures were intact, with some missing during after wet chemical development. Later annealing the sample at 600°C more structures had disappeared while others have shrunk due to the removal of organic fraction from the material. Finally, after calcinating the sample at 1600°C structures have fallen apart and melted, most likely due to the temperature being too high or sintering lasting for too long. These results show, that while still further improvements of fabrication protocol are needed, it is already opening the pathway for additive manufacturing of optical grade active devices at micro- and nano-scales enabling geometrically non-restricted 3D architectures. References:[1] G. Balčas, M. Malinauskas, M. Farsari, S. Juodkazis, Adv. Func. Mater. 33(39), 2215230 (2023); [2] G. Merkininkaitė, et. al., Adv. Eng. Mater. 25(17), 2300639 (2023).

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Abstract: The crystalline hydroxyapatite was coated by a droplets eliminated pulsed-laser deposition scheme. The scratched grains of the coating layers annealed at different temperature were measured by a transmission electron microscope. The electron diffraction pattern indicated that the single crystal was observed at low annealing temperature and polycrystal was observed at high annealing temperature.

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Abstract: We report the possibility of fabricating tetragonal periodic surface structures using circularly-polarized femtosecond laser pulses.

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Abstract: We characterized focused non-Gaussian laser beam profiles using the ablation imprints method, which is an extension of Liu's method that characterizes Gaussian beams. The ablation imprints method is well-established for EUV and x-ray spectral domains and we expanded it into Vis and NIR. We compared its beam characterization results with a conventional method – projecting a magnified image of the focal spot onto a camera. We also present beam characterization and LIDT studies for x-ray laser pulses generated at European XFEL.

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Abstract: The aim of this study is to use the ultrafast laser induce the formation of subwavelength ripples (LIPSS) on the surface of CrTiN alloy thin films (metallic biomaterial interfaces) And, an exploration into the phase and nanocrystal structure of the patterned CrTiN surface is warranted. The results of this investigation demonstrate that ultrafast laser irradiation can enhance cell proliferation on the surface of CrTiN biomedical alloy films through the patterning of subwavelength ripples and nanocrystalline structures. This paves the way for a novel generation of multi-functional surfaces suitable for high-performance medical implants, and medical device technology.

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Abstract: Recently, highly oriented gold NIs (HOG-NIs), showing optical electric field enhancement and resonation with wide range of light (550 nm to 900 nm) were developed by a simple pulsed laser deposition (PLD) method. We tried to fabricate visible light-responsive photocatalyst material by combining titanium dioxide (TiO2) and HOG-NIs. In this study, we will discuss characteristics of HOG-NIs and photocatalytic reactions.

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Abstract: We introduce a portable sequentially timed all-optical mapping photography (STAMP) system with a spectral broadening technique using thin plates, enabling compact and efficient single-shot imaging for laser ablation processes. This system is readily integrable into conventional pump-probe setups with narrow-band probes and captures poorly reproducible picosecond ablation dynamics, enhancing fundamental studies and practical applications in the field.

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Abstract: A group of polymers initially ranging from hydrophilic to hydrophobic and with different optical absorption and thermal properties are modificed by laser irradiation both using NIR fs laser pulses and IR, Vis and UV ns laser pulses. The effect of laser irradiation on wettability is studied and explained according to the chemical and topographical modifications in each case.

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Abstract: This comparative study investigates the generation of Laser-Induced Periodic Surface Structures (LIPSS) on Aluminium (Al) and AISI 304 stainless steel through multi-shot ultrashort pulse laser ablation. Key findings reveal that surface morphology of AISI 304 transitions to high- and low-spatial frequency LIPSS with increasing number of laser pulses, latter one attributed to surface plasmon polariton excitation and fast electron-phonon coupling. Conversely, the higher thermal conductivity of Al leads to microscale structures after the initial pulse, inhibiting coherent periodic modulations by causing stronger scattering in subsequent pulses, thus preventing LIPSS formation. This research underscores the critical influence of initial surface morphology and material properties on the possibility of LIPSS generation, advancing the understanding of optical scattering effects and their impact on surface evolution.

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Abstract: In this study, a ns-boost laser with an average power of 3 kW and a power of 6 kW in boost mode was combined with ultrafast beam deflection using a polygon scanner. The laser beam source had a square top-hat intensity distribution in the imaging plane. The influence of processing parameters such as the pulse energy, repetition rate, scan speed and track distance on the resulting surface roughness and morphology of stainless steel 1.4301 was investigated. The aim was to determine the ideal process window for achieving minimum roughness values with high surface rates at the same time. A high-quality surface was achieved with optimal processing parameters. The initial surface roughness of Sa = 0.275 µm was reduced to a minimum of Sa = 0.096 µm, a 65% reduction in initial surface roughness. Simultaneously, the surface gloss was increased from 125 GU to 400 GU, resulting in a 220% increase in gloss value. This transformation allowed the previously matt surface to become reflective, as shown in Figure 1, thereby enhancing the appearance of the material. The combination of the laser’s boost mode with the polygon scanner allowed the full average laser power to be used for the polishing process. Furthermore, the square top-hat intensity distribution enables higher area rates by significantly reducing the line overlap compared to Gaussian intensity distribution. As a result, a real area rate of up to 156 cm²/s could be achieved. The processing time was only 1.1 min/m², achieving industrial relevant process times for laser beam polishing.

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Abstract: Crystallization through femtosecond direct laser writing (DLW) is a promising technique for inducing oriented nanocrystals and nanostructures in glass materials, including those with photoluminescent properties. Glasses doped with rare earth ions such as Er3+, Eu3+, or Yb3+ exhibit efficient luminescence, including upconversion luminescence (UCL). Furthermore, their spectra are highly sensitive to the ion host, making them valuable for monitoring the effects of the DLW process. While research in this field has been ongoing for several years, the UCL properties related to the irradiation of such luminescent materials with laser pulses are not yet fully understood. In this study, we investigate the UCL properties of Er-doped TeO2-P2O5-BaF2-ZnF2-Na2O (TeP) glass during its crystallization induced by irradiation with 230 fs laser pulses at a wavelength of 1030 nm, with varying repetition rates and energies. A femtosecond laser beam was focused within the glass at a depth of 50 µm in air, using an achromatic lens (NA=0.25), resulting in a spot diameter of 3.9 µm (1/e2). The induced crystalline phase was confirmed each time by Raman spectra and scanning electron microscopy (SEM) and is attributed to barium fluoride (BaF2) crystals. The recorded UCL spectra consist of several broad luminescence bands at 525 nm, 550 nm, and 660 nm, excited by two-photon processes corresponding to electronic transitions between Stark manifolds of the excited lower-lying Er3+ energy levels. These spectra exhibit significant variations depending on the laser parameters and exposure time. The intensity of these bands carries information about the concentration of Erbium ions, thus providing insights into the final outcome of the DLW process. Figure1: Evolution of UCL spectra during DLW in TeP glass with 230 fs laser pulses (a). Widefield (b) and fluorescence (c) microscopic images of irradiated areas of glass sample. (d) Raman spectra of un- (black) and irradiated (red) TeP glass. The inset reveals a photo of polished TeP glass.

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Abstract: Approximately 40% of marketed pharmaceutical active ingredients and 90% of those under development belong to poorly water-soluble compounds. This trend in active ingredient development presents a challenge to the pharmaceutical industry, as poor solubility limits bioavailability in most cases. By reducing the particle size, the active surface increases, which generally improves the dissolution rate and transport characteristics, so that human cells can absorb the active ingredient faster and more efficiently. Our goal was to prove that pulsed laser ablation is suitable for increasing the effectiveness of active pharmaceutical ingredients. In our experiments we were able to significantly reduce the size of the particles of poorly water-soluble non-steroidal anti-inflammatory and pain-relieving active substances (ibuprofen, niflumic acid and meloxicam) by laser ablation in ambient air and distilled water. In this process, lasers with different wavelengths and pulse lengths were used to ablate tablets pressed from commercially available powders.

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Abstract: Silver and gold plates were placed in close contact in a V geometry in order to allow the mixing the two components produced by ablation. In order to ablate both target materials simultaneously and avoid crater formation, the beam spot was scanned along the contact line of the two plates. Energy dispersive X-ray spectroscopy analysis revealed the formation of a significant amount of alloy NPs in addition to pure Au and Ag NPs.

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Abstract: The precise and timely delivery of light to specific locations on a sample is essential for laser material processing. Typically, this task is accomplished with bulky optical elements, including passive components such as lenses and mirrors, and active systems like acoustooptic deflectors and spatial light modulators. In most practical scenarios, it is not possible to place these elements inside a sample of interest. Consequently, most optical systems position all components external to the sample, imposing constraints on both the geometries that can be accommodated and the potential light trajectories. Additionally, scattering can further limit light control inside non-homogeneous media, preventing operations deep inside samples. Here, I will show how ultrasound can address these issues and achieve rapid light focusing and guiding, even inside scattering samples[1]. Our approach is based on exploiting the acousto-optic effect. By sending 1-10 MHz pressure waves inside the sample of interest, refractive index gradients can be generated that act as embedded lenses or waveguides, helping to guide or focus light at depths not possible with standard optical elements. I will discuss the different implementations of this new technology, ranging from the use of acoustic cavities[1,2] to pulsed lasers for ultrasound generation[3] (Figure 1a) and illustrate them with applications such as fluorescence excitation and laser ablation (Figure 1b-c).

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Abstract: With the absence of crystalline defects and their amorphous structure, metallic glasses (MGs) exhibit very interesting mechanical and chemical properties. They have been studied since the 60s in their bulk state (BMGs), but are size limited and complex to synthesize due to their high needed number of elements. More recently, PVD processes enabling high cooling rate of the deposited atoms have demonstrated the easier formation of metastable amorphous metallic phases., together with great freedom in the films’ chemistry. From pure metallic targets, the magnetron sputtering process has already shown its ability to synthesize binary Zr-Cu thin film metallic glasses (TFMGs) over a wide range of chemical compositions (from 13 to 85 at.% of Cu [1]), with low surface roughness together with the absence of grain boundaries, making them suitable for a femtosecond laser treatment [2], to further improve their properties. The work proposed here considers the formation of laser induced periodic surface structures (LIPSS) at the surface of two ternary magnetron sputtered TFMGs (ZrCuAg and ZrTiAg, with interesting biological properties [3]) using infrared ultrashort laser treatment. These textured surfaces are first studied in terms of topographic and chemical modifications, then a focus on the wettability modifications (hydro-phily/phoby) is proposed. Wettability is studied first at the macroscale from the conventional measurement of the water contact angle. On the other hand, the condensation process of water onto the surface is also measured at the microscale by in situ measurements conducted in an environmental scanning electron microscope (ESEM). Such a complementary small-scale method gives key information on the interaction of very small water droplets with the textured surface, opening the way to biological behavior of such surfaces. [1] M. Apreutesei, et al., “Zr-Cu thin film metallic glasses: An assessment of the thermal stability and phases transformation mechanisms”, Journal of Alloys and Compounds, 2015 [2] M. Prudent, et al., “Initial morphology and feedback effects on laser-induced periodic nano-structuring of thin-film metallic glasses”, Nanomaterials, 2021 [3] A. Etiemble, et al., “Innovative Zr-Cu-Ag thin film metallic glass deposited by magnetron PVD sputtering for antibacterial applications”, Journal of Alloys and Compounds, 2019

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Abstract: To develop remote isotopic analysis for the nuclids with small isotope shifts, Doppler-free fluorescence spectroscopy of Ca was performed using laser ablation plume. Counter-propagating laser beams from two external cavity diode lasers were used to irradiate the plume in order to excite the ground-state Ca atoms to the 1D2 state through a double resonance scheme of 1S0 → 1P1 → 1D2. Subsequently, we measured fluorescence spectra associated with the relaxation from the 1D2 to 1P1 states. The linewidth measured at 1 ms delay after ablation under helium gas pressure of 70 Pa was found to be less than 70 MHz, which was about 1/30 of the linewidth of the Doppler-limited fluorescence spectrum. We evaluated analytical performances such as linearity of the calibration curve, limit of detection, and measurement accuracy using fluorescence signals of three naturally occurring Ca isotopes (i.e., 40Ca, 42Ca, and 44Ca). The obtained results suggest that this spectroscopic technique is promising for remote isotopic analysis of nuclides with small isotope shifts

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Abstract: We have demonstrated an effective process to reduce the secondary electron yield of any material through the use of pulsed laser processing. This is being directly applied to reduce electron clouds at the LHC.

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Abstract: The isolation of circulating tumor cells (CTCs) with high cell viability for further multi-omic analysis and organoid generation is a turning point in modern oncology. In recent years, CTCs and CTC cluster research have completely changed the roadmap of disruptive translational technologies in oncology, mainly because if adequate CTC isolation without cell modification could be achieved in liquid biopsies, this would mean a paradigm shift in clinical and preclinical oncology. In this work, we present a proof of concept of CTCs isolation using Blister Actuated Laser Induced Forward Transfer (BA-LIFT) and demonstrate that the technique is not only valid for isolation and further single cell sequencing for multiomic analysis, but also for CTCs cell culture, which opens the possibility of using them to study tumour biology and generate new patient-derived models.

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Abstract: functionalities like waveguides, Bragg structures or artificial birefringence in various glasses and crystals. In addition, cutting and welding of different glasses has been demonstrated with ultrashort pulses. All these processes rely on a well-controlled nonlinear energy deposition inside the transparent material. This technique has until now no equivalent for narrow bandgap semiconductors, especially for silicon [1], which is the backbone of today’s semiconductor industry. The reason is the different transparency range, the high refractive index leading to severe beam distortions and mainly the significantly higher nonlinearities, hindering a precisely localized energy deposition inside the material. In this presentation, we will report on the analysis of the nonlinear interaction of intense ultrashort laser pulses in the infrared spectral region with silicon. Based on these investigations the inscription of waveguides in the longitudinal [2-3] as well as transversal regime [4-5] will be demonstrated. The potential to transfer this technology to other narrow bandgap semiconductors will be discussed. Acknowledgements: German Federal Ministry of Education and Research (project RUBIN-UKPiño; grant no. 03RU2U033H); Max Planck School of Photonics supported by BMBF, Max Planck Society, and Fraunhofer Society. References: [1] M. Chambonneau, D. Grojo, O. Tokel, F. Ö. Ilday, S. Tzortzakis, et al. and S. Nolte, “In-Volume Laser Direct Writing of Silicon—Challenges and Opportunities,” Laser & Photonics Reviews 15, 2100140 (2021). [2] G. Matthäus, H. Kämmer, K. A. Lammers, C. Vetter, W. Watanabe, and S. Nolte, “Inscription of silicon waveguides using picosecond pulses,” Optics Express 26, 24089–24097 (2018). [3] H. Kämmer, G. Matthäus, K. A. Lammers, C. Vetter, M. Chambonneau, and S. Nolte, “Origin of Waveguiding in Ultrashort Pulse Structured Silicon,” Laser & Photonics Reviews 13, 1800268 (2019). [4] M. Chambonneau, M. Blothe, Q. Li, V. Yu. Fedorov, T. Heuermann, et al., “Transverse ultrafast laser inscription in bulk silicon,” Physical Review Research 3, 043037 (2021). [5] M. Blothe, A. Alberucci, N. Alasgarzade, M. Chambonneau, S. Nolte, “Transverse Inscription of Silicon Waveguides by Picosecond Laser Pulses,” Laser Photonics Rev 2400535 (2024).

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Abstract: Ultrashort pulsed laser ablation in organic liquids induces a plethora of chemical reactions that form diverse molecular and material products from decomposition of organic molecules. This presentation will highlight recent progress in my group towards elucidating reaction pathways for laser ablation of neat organic liquids using mass spectrometry to characterize molecular products of laser ablation and optical spectroscopy to measure laser-induced reaction kinetics. Knowledge of these reactions can advance laser ablation synthesis of fluorescent carbon dots and metal nanoparticles with protective carbon shells.

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Abstract: Studies on thermal waves induced by ultrashort laser pulses on surface and in the bulk of wide bandgap semiconductors will be reported.

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Abstract: Pulsed laser ablation in liquid (PLAL) is a sustainable and swift approach of synthesizing nanoparticles (NPs) and nanocomposites. In this method, a high energy pulsed laser beam is focused on a target (mostly metallic in nature) which is submerged in a transparent liquid such as distilled water (DW). Due to high photon density, various dynamic processes occur at the solid-liquid interface such as plasma formation, shockwave emission, cavitation bubble oscillations, and eventually, the formation of NPs which are dispersed in the liquid and form nano-colloid solution. Due to close correlation between NPs and the dynamics of laser ablation, laser parameters such as laser wavelength, pulse duration, laser fluence, and external fields play a crucial role in determining the properties of NPs. Target geometry also affects the properties of NPs, such as its size, morphology, and optical properties. Different morphologies of target such as wire-shaped target have been studied and it has been found to increase the efficiency of laser ablation. In the present study, cavitation bubble dynamics of PLAL, conducted in a confined space is studied using shadowgraphy. A channel is fabricated at the center of the metal target and the laser is incident inside the channel. The walls of this channel, or a valley, will constrict the laser produced plasma and affect the dynamics, and hence the NPs. Different widths (2 mm, 3 mm, 4 mm) of this valley have been studied so that the effect of enhanced confinement of laser ablation spot can be studied. Temporal evolution of cavitation bubble size, pressure and temperature as well as the effect of confinement on NPs will be presented in the conference.

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Abstract: A laser with an emitted wavelength of 1030 nm and a pulse duration of 10 ps was used to irradiate fields by varying the fluence, number of passes and burst-modes in combination with the number of burst pulses on cemented tungsten carbide. A total of 100 different burst-pulse-number combinations was used, consisting of MHz- and GHz-bursts, or a combination of those. To compare the burst-mode results with the single pulse regime, the fluence for single pulses was varied between 0.5 J/cm² and 200 J/cm². For the combined MHz- and GHz-burst with up to 10 pulses each and therefore a total of 100 burst-pulses max, fluences of 0.5 J/cm² (maximum of 50 J/cm² per burst) to 2.0 J/cm² (maximum of 200 J/cm² per burst) were used. Subsequent analyses using SEM, confocal 3D laser scanning microscope, light microscope and EDX were utilised for qualitative and quantitative analysis. Using MHz-bursts, an increase in ablation efficiency was obtained with an increase in surface roughness compared to the single pulse regime. Accordingly, this burst-mode is suitable for a high ablation rate. The GHz-burst yielded a significantly lower removal rate, resulting in reduced efficiency, but with the advantage of improved surface roughness. The combination of MHz- and GHz-burst enables the highest power throughput with simultaneously increased efficiency compared to the single pulse regime. A disadvantage is the melt build-up, which contributes to a significant increase in surface roughness. By post-treatment of the surface using the GHz-burst, these deposits of melt can be almost completely removed and the surface smoothed. Efficient ablation using MHz-burst or a MHz/GHz-burst combination with subsequent smoothing using GHz-burst, thus results in high ablation efficiency with good surface quality.

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Abstract: Recent advancements in industrial-grade systems now allow ultrashort, high-intensity femtosecond laser pulses in the UV domain, enhancing precision and efficiency in micro processing. These pulses minimize heat affected zones and outperform traditional IR or visible spectrum methods. The presentation focuses on two-beam interference patterning of silicon and optical materials using femtosecond UV pulses, enabling the creation of homogeneous nanoscale gratings on centimeter-scale areas. Introduced further etching in a 1% KOH solution, resulted in a tenfold increase in structure height. The periods of fabricated harmonic gratings were in a range of Λ = 600-700 nm.

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Abstract: Using multiple femtosecond laser pulses to irradiate a sample on the same spot, the ablation thresholds depends on the number of irradiated pulses. The multi-shot ablation threshold can be significantly lower than the single-shot ablation threshold because of the incubation effect [1]. Ultra-high precision nanomilling of copper to depths of several nanometers and post-fabrication bi-direction tuning of silicon microring resonator circuits [2] were demonstrated using multiple femtosecond laser pulses with fluences below the single-shot ablation threshold by taking advantage of the incubation effect. However, the detailed processes for multiple-shot irradiation of a material at fluences well below single-shot ablation threshold is not well understood. In this study, we utilize the silicon microring resonator as a novel tool to better understand the physics of incubation effects. The refractive index change induced by laser irradiation can be detected with unprecedented sensitivity by measuring the resonant wavelength shift of a silicon microring resonator. In a previous study [4], we have determined the thresholds for refractive index change irradiated with single femtosecond laser pulses at 400 nm and 800 nm wavelengths. The threshold for permanent index change at 400 nm wavelength was determined to be 0.053 J/cm2 for single-shot irradiation， which agrees with previously reported threshold values for femtosecond laser melting of crystalline silicon. However, the threshold for index change at 800 nm wavelength was found to be 0.044 J/cm2 for single-shot irradiation, which is five times lower than the previously reported threshold values for visual change on the silicon surface. The discrepancy for 800nm irradiation is attributed to crystalline modifications below the melting temperature that were not observed before. In this study, by irradiating silicon microring resonators with femtosecond laser pulses on the same location at fluences significant below the single shot thresholds for refractive index change, while measuring the shot-to-shot evolution of refractive index changes, information about the dynamics of incubation effects can be obtained. Interestingly, our results indicate that the incubation effects behave significantly differently for irradiation at 400nm wavelength as compared to at 800nm wavelength. The experimental data of shot-to-shot refractive index change for silicon irradiated by ultrashort laser pulses with fluences significantly below the visual damage threshold will be valuable for the development of detailed models for incubation effects.

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Abstract: In recent decades, laser-matter interactions in ultrafast laser ablation has been extensively studied. Numerous simulations exist today that primarily provide a qualitative understanding of laser ablation with single pulses, while the precise quantitative prediction of final state and time-resolved observables remains challenging. Moreover, the majority of experimental approaches to study laser ablation are performed with multiple pulses, making it difficult to experimentally validate single-pulse simulations. Here, we present new experimental validation of models for laser ablation in air and liquid as well as for laser fragmentation of microparticles.

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Abstract: The research explores the use of femtosecond laser burst modes in the GHz regime to enhance the efficiency of micro-drilling in various transparent materials such as glass, fused silica, diamond, silicon carbide and sapphire. By employing burst modes with a high number of sub-pulses, the depth of micro-machined channels is significantly increased compared to conventional single-pulse methods. The study demonstrates the feasibility of achieving deep channels spanning several millimeters with good quality, in several different materials. These findings not only improve micromachining throughput for TGVs but also indicate the versatility of femtosecond laser techniques for various materials beyond electronics, potentially benefiting fields like advanced optics or biomedical devices.

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Abstract: Irradiating a thin gold film (film thickness approx. d_z = 100 nm, including an adhesion layer of 20 nm chromium) on a glass substrate with single-pulsed ultrafast laser radiation (pulse duration τ_H = 40 fs, wavelength λ = 800 nm) results in a step-like topography of the ablation structure, including the so-called gentle- and strong ablation substructure (Fig. 1a). Simulating the laser-matter interaction by two-temperature modeling in conjunction with hydrodynamics (TTM-HD) [1] (Fig. 1c) combined with ultrafast pump-probe metrology over 10 decades of time scales (fs- up to µs-range) (Fig. 1b) provides fundamental insights into ablation and increases the understanding of the process of ablating thin metal films [2,3]. Thereby, ultrafast pump-probe imaging ellipsometry [4] enables to measure the amount of absorbed energy, whereas a comprehensive combination of ultrafast pump-probe imaging reflectometry [2-5] and interferometry and modeling allows reconstructing the transient topography of all ablated substructures. This complementary approach reveals that a closed layer of liquid material formed by spallation remains undamaged until approximately 30 ns. In the case of phase explosion, the omnidirectional expanding gas-liquid mixture deforms this closed layer of liquid material. After 100 ns the closed spallation layer ruptures.

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Abstract: This paper describes two specific methods for achieving directed growth of Schwann cells, a type of glial cells that can support the regeneration of the nerve pathway by guiding the neuronal axons in the direction of their alignment. One method implies the exposure of a poly(ethylene terephthalate) (PET) foil to a KrF* laser beam, that induces the generation of laser-induced periodic surface structures (LIPSS). The other method uses aligned polyamide-6 (PA-6) nanofibers produced via electrospinning on a very fast rotating structured collector. These collectors can be covered by antiadhesive laser-induced or mechanically inscribed periodic surface structures, which enable easy nanofiber detachment, without additional effort. For both methods, we show that Schwann cells grow in a certain direction, predetermined by nanoripples and nanofibers orientation. In contrast, cells cultivated onto unstructured surfaces or randomly oriented nanofibers, show an omnidirectional growth behavior.

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Abstract: Ultra-thin two-dimensional (2D) nanostructures, traditionally obtained from the cleavage of the weak interlayer van der Waals (vdW) forces, have been spotlighted over the last two decades, sparking a rapidly growing research interest for their potential applications. However, the application of vdW 2D materials in nanotechnology is hampered, inevitably, due to the lack of their stability under ambient conditions. As a result, the perspective to synthesize ultra-thin 2D sheets from non vdW bulk materials and study their physicochemical properties became very challenging, given their stability, easy processing, and abundance on earth. Until now, the preparation of non vdW 2D materials was regarded inaccessible due to the high surface energies and the lack of anisotropy in the 3D bonding network. [1] Unexpectedly, the recent progress in liquid phase exfoliation of covalent/ionic crystals has led to the exfoliation of a series of atomically thin non vdW layered nanostructures from naturally grown bulk metal minerals. The 2D analogs of hematite and magnetite, called hematene and magnetene, constitute the two archetype 2D iron-ore non-vdW materials. [2,3] These nanostructures display exceptional magnetic and photo/electrocatalytic properties which are superior to those of their bulk counterparts due to quantum confinement and surface effects. [2,3] In addition, because of their interesting optoelectronic features, it is speculated that hematene and magnetene could be used for innovative photonic and optoelectronic devices. [2,3] However, such studies are still in their early stages, as investigations pertaining to the ultrafast nonlinear optical (NLO) properties of non-van der Waals 2D materials are rather scarce. In this context, the present work constitutes the first systematic investigation, to the best of our knowledge, of the ultrafast NLO response (NLO absorption and refraction) and its temporal evolution in hematene and magnetene 2D nanostructures prepared via a green synthesis method and dispersed in water. More specifically, for the assessment of their ultrafast NLO response and its dynamics, Z-scan and optical Kerr effect (OKE) measurements were performed using 50 fs, 400 nm laser pulses. The results of the present work strongly suggest that hematene and magnetene can have applications in a wide range of photonic and optoelectronic applications.

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Abstract: In the field of nuclear energy, advancing reactor technologies require the precise study of nuclear fuel behavior under different irradiation conditions, driving a shift towards localized data analysis within the fuel pellet. However, challenges remain in obtaining appropriately sized samples for thorough investigation, typically ranging from a few hundred microns to a millimeter. Building upon preliminary studies conducted on model materials [1], our methodology focuses on applying sub-pico laser ablation for micromachining to manufacture samples made of uranium dioxide (UO2). By integrating a numerical model to calculate thermal effects and pairing it with surface temperature measurements obtained using a high-speed thermal camera, our study aims also to quantify and minimize the heat-affected zone. Such control of the affected zone is essential to preserve the microstructure and inherent properties of the samples under investigation. In this talk, we present our first results to produce samples within a vacuum chamber under controlled atmospheric conditions together with corresponding thermal behavior modelling. The transition from model materials to UO2 samples marks a significant advancement in our research, contributing to a deeper understanding of nuclear fuel behavior under various irradiation conditions.

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Abstract: Transparent materials hold immense potential for various applications ranging from optics to biomedicine, telecommunication, and sensing, necessitating precise control over their surface properties. In this framework, Direct Laser Interference Patterning (DLIP) emerges as a versatile technique for achieving subwavelength periodic structures with a high aspect ratio for a wide range of materials [1,2]. By exploiting interference patterning mechanisms, DLIP enables tailored surface functionalities such as anti-reflective, superhydrophobic, and anti-bacterial properties. Moreover, DLIP's compatibility with various transparent materials, including glass, polymers, and ceramics, underscores its versatility and potential for widespread application. Importantly, the technique raised interest in the last few years since it allows for minimising waste generation and chemical usage, contributing to a greener and safer manufacturing environment. Nowadays, DLIP appears to be the right compromise to achieve surface features with size down to a few 100s of nm while running at competitive throughputs. In this work, the DLIP technique is employed to produce functionalised fused silica, polycarbonate, and sapphire (Figure 1). A state-of-the-art processing setup is employed to shape the 100s-nm nanostructure features to obtain highly homogeneous morphologies in different regimes of interaction (laser pulse duration from 100s of femtosecond to a few picosecond). Various surface functionalities are validated to link the process parameters to the functional behaviour of the patterned surface.

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Abstract: Metal darkening by means of femtosecond and picosecond lasers has been extensively studied concerning both the reflectivity decrease mechanism and the structure forming process on the surface. However, the literature of the darkening with nanosecond pulse laser irradiation remained scarce, leaving open questions related the process. In this work we aimed to study the effect of nanosecond laser irradiation on different metals (copper, titanium and aluminum) with special regard to the evolution process of the relevant micro- and nanostructures and their relation with the alteration of the optical properties.

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Abstract: We would like to present a new method utilizing an XFEL (X-ray Free-Electron Laser) to visualize surface morphology dynamics and subsurface atomic structure employing grazing-incidence X-ray scattering. We will report our recent experimental results and discuss future perspectives.

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Abstract: 4H-silicon carbide (4H-SiC) based power electronics are pivotal for the transition to e-mobility, efficient energy distribution and storage. Their superior properties compared to silicon, including a wider bandgap, higher thermal conductivity, and mechanical robustness, have driven widespread adoption but also present challenges in the semiconductor production chain. Consequently, laser micromachining has become indispensable in the SiC- device production. The combination of ultrashort pulsed lasers with high average power and pulse repetition rates (PRR), coupled with fast beam polygon mirrors (speed > 1 km/s), has been shown to improve the throughput by a factor of 7. One concomitant effect of such processes is thermal incubation, which can detrimentally affect the precision of the laser process and the end device. However, for hard-to-machine materials like 4H SiC (Eg=3.2eV and thermal conductivity 280Wm^(-1) K^(-1)), increasing the thermal budget may reduce the threshold and enhance throughput—a novel approach not explored in prior studies. In this paper, we demonstrate polygon scanner-driven laser dicing of 4H-SiC (Fig. 1a). The experiments were performed on the Si-face of an EPI-ready n-type 4H-SiC substrate (thickness=350 µm), utilizing a commercial ultrafast laser system (AMPHOS 2000, λ=1030nm, τ=0.9-15 ps, maximum average power = 200 W) and a polygon scanner (Hochschule Mittweida). The effective laser beam waist and the modification threshold were determined via Liu fit to be ≅20μm 1/e² and 1.82J/cm² respectively. Lines were scribed along the <1120> direction with constant τ (3 ps) and PRR (1 MHz) while laser pulse energy, number of scans (n), and pulse to pulse pitch were varied based on the modification threshold. We report an increase in dicing throughput by an order of magnitude in comparison to mechanical dicing and standard ablative laser dicing. We present a qualitative and quantitative analysis of the microstructures, revealing the interplay of temporal and spatial distance via number of scans and scanning speed (pitch) which is crucial in minimizing the kerf loss.

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Abstract: To gain a deep insight into the dynamics of laser-excited processes in bandgap materials, modification of fused silica has been studied using double 800-nm laser pulses with fs/ps separation times. The effects of laser-generated free-electron plasma shielding, its characteristic time, and the modification level as a function of time delay and laser energies in the pulses have been analyzed. Experimental results are supported by numerical simulations of double laser pulse propagation in nonlinear media based on Maxwell’s equations.

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Abstract: To observe supernova relic neutrino events, gadolinium (Gd) sulfate is dissolved in the Super-Kamiokande (SK) 50 kt water Cherenkov detector aiming at improving the detection efficiency of neutrons. In addition to neutron absorption, Gd3+ ions can be excited by the Cherenkov light from cosmic muons and the subsequent emission at 312 nm is a possible background (BG) source for Cherenkov signal detection. In this study, an experimental setup based on time-resolved laser-induced luminescence spectroscopy was constructed to measure spectroscopic data of Gd3+ ions in water such as molar attenuation coefficient and observed emission lifetime. A simulation study was performed assuming the geometry of the SK detector to estimate the influence of the Gd3+ ion emission BG on the detector. Development of a portable monitoring system using our spectroscopic technique will also be mentioned, which enables real-time measurements of Gd3+ ion concentration and emission lifetime without contamination during water sampling.

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Abstract: Photocatalysis, harnessing sunlight, is crucial for addressing energy generation and environmental pollution. Perovskites are extensively studied as potential photocatalysts, particularly, for water splitting reaction. Strategies for enhancing the photoelectrochemical (PEC) activity of complex oxide materials involve adjusting their intrinsic structural, topographical, and stoichiometric properties. Here, we focus on the fabrication of perovskite thin films using Pulsed Laser Deposition (PLD) and evaluate their PEC performance in terms of film thickness, deposition pressure and heterostructure’s arhitecture. We examine the influence of the structural parameters with film thickness and oxygen content in epitaxial LaFeO3 (LFO) thin films, noting the formation of self-assembled nanodomains for films thicker than 14 nm due to strain induced by differences in lattice constants between the material and the substrate. The multilayer configuration based on LFO/BFO/STON and BFO/LFO/STON exhibits a strong dependence on the interface/surface properties of the film. By utilizing Nb:SrTiO3 as a conductive substrate and 0.5 M NaOH aqueous solution for PEC measurements, we analyze the relationship between photocurrent density, onset potential, and the structural, topographical, and optical characteristics of complex oxide-based photoelectrodes using X-ray diffraction, high-resolution transmission electron microscopy, and ellipsometry. The catalytic activity under dark condition is evidenced Potentiodynamic PEC analysis reveals the highest photocurrent density values (up to 1.2 mA/cm2) and excellent stability over time for the thinnest LFO/Nb:SrTiO3 sample prepared at 0.6 mbar O2, showing both cathodic and anodic behavior. Further enhancement in photocurrent density is expected through the use of a multilayer photoelectrode incorporating LFO and BFO materials. Importantly, perovskite-based thin films exhibit efficient hydrogen evolution from water, confirmed by gas chromatography under constant illumination. The enhancement of photocurrent density can be achieved through the utilization of a multilayer photoelectrode incorporating LFO and BFO materials. The objective of this investigation was to merge the robust ferroelectricity of BFO with the excellent absorption properties and high chemical stability of LFO, thereby creating novel photocatalysts with improved activity in photocatalytic reactions.

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Abstract: It will be shown that the removal efficiency on Stainless Steel (AISI 304) could be increased by a factor of 2.8 when using laser bursts with 1,300 intra-burst pulses. The highest removal efficiency was achieved at 10 m/s, steadily decreasing with faster laser beam moving speeds. The influence of the intra-burst pulse number and scan speed on material ablation, the effect of burst repetition frequency and average laser power will be discussed. Results obtained will be compared with material removal in the nanosecond pulse regime.

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Abstract: The two-photon lithography enables the fabrication if complex freeform with resolutions below the diffraction limits if the optical system. Complex interactions between the fabrication parameters and the material define the achievable resolution and therefore the dimensions of the induced voxel. This work aims to create an insight of the resolution limits of diverse materials of a commercial workstation that is transferable to other systems. Therefore, the process windows of the materials are investigated and the voxel dimensions defined.

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Abstract: Pump-probe microscopy is an essential tool for studying laser-matter interaction. However, imaging of laser-induced surface acoustic waves (SAWs) has not been possible with a conventional setup. In this study, we present a new approach to detect laser-induced SAWs on silicon and thin metal films with a conventional setup. The results suggest that background filtering based on non-linear absorption reveals the SAWs. In the future, this effect could provide new insights into the phenomena of laser-matter interaction, photoacoustic effects, especially at high intensities, and materials science.

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Abstract: Laser processing offers a powerful engineering solution for functionalizing the surface of materials. One specific case of interest is the fabrication of nano- and microstructured silicon by femtosecond laser irradiation, generating Laser Induced Periodic Surface Structures (LIPSS) [1]. In the case of silicon (Si), this functionalization may reduce the material’s reflectivity due to multi-reflection processes [2]. In this work, an approach to improve the light absorption of silicon in the ultraviolet-to-near infrared spectral range via fs laser processing is described and discussed. The approach is based on the fast cost-effective fabrication of fs laser (1030 nm and 515 nm) -induced micro-spikes in silicon in air atmosphere. The impact of the irradiation conditions on the size, period and aspect ratio of the structures, as well as on the light absorption of the material has been studied. Varying pulse number and laser fluence up to 1.8 J/cm2 we have been able to tune the size and period of the processed structures. Additional tuning of the laser repetition rate from 50 to 500 kHz has allowed the fabrication of spikes with high aspect ratio, leading to an extremely high absorption, above 95% from 250 nm to 1100 nm. In addition, a post-processing annealing has been performed in order to recover the crystallinity of the sample after irradiation, in order to overcome the induced factors that could compromise carrier lifetimes. Applications of the structures to the field of photovoltaics will be presented. Acknowledgements: This work has been funded by the research grant HyperSolar (TED2021-130894B-C22) from the Spanish Research Agency (AEI, Ministry of Research and Innovation), the European Regional Development Fund (ERDF) and NextGenerationEU. References: [1] J. Bonse, A. Rosenfeld and J. Krüger, J. Appl. Phys. (2009), 106: 104910; [2] B. Franta, E. Mazur and S.K. Sundaram, Int. Mat. Rev. (2018) 63(4): 227-240.

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Abstract: It is well known that the friction between two different surfaces can be controlled by applying specific textures tailored to the application. Moreover, innovative machine learning methods can optimize surface texturing designs for various concrete applications, like friction optimization in piston seals. In this regard, laser is a phenomenal tool for the fabrication of different patterns in flat and 3D surfaces. The flexibility provided by adjustable process parameters that can be modified, such as laser power, spot size, wavelength, pulse duration or repetition rates, enables the creation of surface patterns with a large range of shapes and sizes. Over the past few years, a great amount work has been devoted to the fabrication of textures with smaller and smaller features, reaching lateral sizes within the range of the micron, which has a strong impact on the productivity. Some of the most advanced laser texturing techniques require of the use of optics with high magnification or, in some particular cases, even complex optics. This makes the use of fast scanning strategies impractical, thus, point towards parallelization strategies as the most appealing approach to improving the productivity of laser texturing processes. This work reports on the use of Diffractive Optical Elements (DOEs), in combination with high magnification optics, with the aim of tackling at the same time the optimization of the productivity of laser texturing processes for friction reduction applications that require of features with lateral sizes in the range of a very few microns. In this way the morphology, productivity and finishing of periodic textures fabricated making use of DOEs with different arrangements of split laser beams, in terms of number of parallel beams and physical distribution, will be presented and discussed, proving that Parallel laser texturing with DOEs is one of most effective solutions to reach high productivity with high lateral resolution.

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Abstract: This study employs molecular dynamics simulations to investigate the fundamental mechanisms of ultrashort pulse laser ablation of silver films of various thickness. It analyzes density fluctuations leading to an explosive phase decomposition and their connection to the classical nucleation theory, as well as the transition from the superheated liquid to a mixture of vapor and liquid droplets upon the expansion of the ablation plume. The implications of the ablation dynamics for droplet size distribution are analyzed. The computational predictions are validated by comparing the scattering and reflectivity of the ablation plume calculated in the simulations with those measured in pump-probe optical imaging.

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Abstract: Transparent conductive oxide (TCO) thin films are used as front side electrodes in various innovative, high-efficiency solar cell concepts, due to their high conductivity and transparency over a large wavelength range. Many of these solar cell types, such as a-Si/c-Si heterojunction solar cells, have a limited thermal budget. In this work, we address the challenge, of annealing transparent thin films on temperature sensitive solar cells by using UV ns and ps pulsed laser processes. The annealing impact and depth selectivity of four different UV laser systems was examined; three ns-lasers (λ = 248 nm, 308 nm, 343 nm with tp = 25 ns, 25 ns, 15 ns, respective-ly) and a picosecond laser (λ = 355 nm, tp = 10 ps). We demonstrate depth selective thin film crystallization with modification depths below 40 nm in TCO thin films without degradation of the underlying, temperature sensitive solar cell. Furthermore, our results suggest the existence of different annealing mechanisms and time dynamics, depending on the as-deposited TCO properties. The understanding of the laser material interaction and annealing dynamics is further investigated, since it is crucial for implementing optimal laser annealing processes for high efficiency solar cells.

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Abstract: This contribution deals with the effects of low fluence laser ablation on metallic surfaces. Initially, our resluts show how lowering the pulse fluence below the threshold for laser ablation leads to the formation of an oxide layer on the surface, altering its chemical composition and consequently its corrosion properties. If the pulse fluence is increased slightly above the threshold fluence, LIPSS are formed. We investigates how the ambient atmosphere, in particular air, nitrogen and argon, affects the formation of LIPSS when both picosecond and nanosecond pulses are used. In particular, variations in beam scanning speed and pulse fluence were observed to impact the properties of the fabricated LIPSS, with the effects based on pulse duration and atmospheric conditions. Results show that the formation of LIPSS is strongly influenced by the surrounding atmosphere, with picosecond pulses showing less dependence but still exhibiting variations in rib curvature based on atmospheric conditions. In contrast, nanosecond pulses led to LIPSS formation only in air, indicating a relationship with surface oxidation. Further analysis using various techniques such as EDS, XPS, AFM and FIB cross-sections elucidated the differences in LIPSS composition and structure between picosecond and nanosecond pulses, highlighting the significant impact of atmospheric conditions and pulse duration on the formation of LIPSS on stainless steel surfaces.

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Abstract: This study proposed a laser-heating oxidation technology using maskless ultraviolet laser irradiation on the surface of alloys SS316 and Ti-64. The laser-marked surface generated an oxide layer without ablating materials and produced the color change between oxides and raw materials. The laser power, scan speed, and scan spacing were adjusted to mark QR codes for product identification. The tested results demonstrated that a higher laser power, slower scan speed, and lower scan spacing produced a dark oxide layer. This was due to a phenomenon of high thermal accumulation. Furthermore, the image recognition by the smart phone was more stable when the QR code was marked with a scan speed of 60 mm/s and a scan spacing of 40 μm. The marked QR codes for Ti-64 have significantly black colors compared to those for SS316. QR codes on surfaces SS316 and Ti-64 were found to have the ability to recognize as Fa above 156.3 J/cm2. The elemental oxygen content of SS316 and Ti-64 treated with 625 J/cm2 was greater than 3.5 and 50.8 times compared to the untreated, respectively. The grain size of SS316 and Ti-64 before and after maskless laser marking does not have a significant change in the lattice structure. The proposed approach can be widely applied in IoTs for manufacturing components that need to use QR codes in conjunction with the barcode reader to quickly manage inventory.

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Abstract: The combination of laser-induced breakdown spectroscopy (LIBS) and k-nearest neighbors (kNN) algorithm was used to a dependable classification model of kimchi products consumed in South Korea. In the Korean markets, 125 kimchi samples were collected; 73 imported from China and 52 produced in South Korea. Based on the evaluating "interclass distance" of the seven strongly observed emission lines (C I, H I, O I, Mg II, Ca II, Na I, and K I), the K I and Mg II emissions were found to be effective and used to model the sample classes (China and South Korea). The best kNN model showed 92.8% classification accuracy. Our results indicate that the combination of the simple elemental analysis techniques, LIBS, and a classical non-parametric modeling approach, k-NN, is promising as a practical methodology for origin distinction of kimchi in markets.

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Abstract: In the context of target fabrication for proton fast ignition laser fusion experiments, we present studies that help meeting the strict requirements posed to the quality of laser machined target components. We analyze the energy deposition of ultrashort laser pulses in a polyvilyl chloride sample using two-color pump-probe shadowgraphy to prevent unwanted bulk material change. Additionally, we study the mitigation of material redeposition below and above a trimethylolpropantriacrylat sample, by evaluating the effect of a water reservoir under the sample, and by examining the potential of MHz and GHz bursts to reintegrate redeposited particles on the sample surface.

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Abstract: Classic top-down and bottom-up ablation techniques are the most established approaches for precision glass milling with an ultrafast laser. The bottom-up technique is superior to the top-down approach in high milling rates due to the more effective material removal mechanism. However, this technique is unsuitable for milling non-transparent glasses and for 3D glass processing (processing from both sides). Hence, a slower top-down technique remains a more promising technique for such applications. Different studies showed that milling rates of the top-down approach could be improved using MHz and GHz burst modes. However, no studies were reported on glass ablation with femtosecond laser BiBursts (GHz bursts in MHz burst). In this study, we used a femtosecond laser (Carbide from Light Conversion) working in BiBurst mode to ablate fused silica glass. Results indicated a similar material-removing mechanism to a bottom-up technique which significantly increased glass milling rates.

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Abstract: The burst regime has already shown benefits in processing different materials. Most of the studies are done with direct ablation as it allows the ablation of non-transparent materials. However, glasses could also be machined from the bottom side allowing the formation of straight walls. Furthermore, lower damage threshold of the bottom surface and ablated particle removal with the help of shockwave and gravity results in higher cutting speeds. In this work, we investigated the bottom-up machining of soda-lime glass using GHz bursts. Femtosecond laser Carbide CB3-40W (Light Conversion) emitting 1030 nm wavelength was used in the experiment. We investigated different pulse durations and number of pulses per GHz burst for soda-lime glass cutting. The cutting was done with the beam focused on the bottom surface of the 4.8 mm thickness sample. The positioning of the beam in the X and Y axes was achieved with a galvanometer scanner and the Z position was controlled with a linear motor stage. The beam was focused with a 100 mm focal length telecentric f-theta lens. The burst regime allowed us to achieve ~ mm/s cutting speed on 4.8 mm thickness soda-lime glass. Furthermore, we demonstrated 18 mm thickness sample cutting together with complex contour cutting for 4.8 mm thickness glass. These results show, that bottom-up cutting using a burst regime is a compelling technique for glass processing.

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Abstract: We have attempted localized and shallow doping by using excimer laser irradiation for introduction and activation of dopants. Al was used as a dopant and deposited with 6-nm-thickness by sputtering on p- or n-type Si substrates. The deposited Al films on Si substrates were irradiated 10 times with a KrF excimer laser. A good pn junction was formed while maintaining surface flatness under the condition of fluence 0.8 J/cm2 in the results of n-type Si substrate.

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Abstract: The purpose of this work is to model laser ablation of silicon on an atomistic scale in combination with a mesoscale model for the description of the electron-phonon interaction and an electron-temperature dependent interaction potential. As an application we investigate the non-thermal material dynamics of strongly excited silicon during ultra-fast laser ablation.

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Abstract: Synthesis of novel multi-element nanomaterials is a very important task for life science applications in order to perform simultaneously different actions. Pulsed laser ablation in liquids (PLALs) is a very promising technique for forming of chemically ultrapure single- and multi-element nanostructures in an easy and fast way. Recently, we have demonstrated successful merging of semiconductor and metallic elements in form of one nanoparticle (NP) that is still unexplored and challenging niche of the laser-matter interaction field [1,2]. In this research, plasmonic nanocomposites (NCs) based on either laser-generated or chemically prepared semiconductor nanoparticles (silicon or carbon) were synthesized by means of PLALs technique. For this purpose, noble metals were immersed in aqueous colloidal solutions of semiconductor NPs and were treated with a pulsed laser irradiation (1030 nm, 6 ps, 10 kHz, 50 µJ/pulse). The presence of both metallic and semiconductor elements in NPs (confirmed by EDX studies [1]) ensure effective plasmonic and paramagnetic modalities that can be employed for sensing applications. One can easily design the NCs with tuned spectral position [2] and efficiency (Figure 1a) [2,3] of plasmonic properties by changing a metallic target and laser irradiation time, respectively. The latter reflects the variation of the irradiation time-dependent gold content studied by ICP-MS (Figure 1b). Nevertheless, the variation of the laser fluence affects neither mean size nor size distributions of plasmonic semiconductor-based NCs [4]. However, the chemical composition strongly depends on the mean size of NPs: the gold content decreases with the size of NCs [1]. Thus, one can manage the performance of the nanocomposites by playing with the experimental conditions during the laser synthesis. Indeed, beside the previously reported SERS biosensing using Si/Au NCs, we recently demonstrated controlling of the ultrafast laser-induced heating of colloidal solutions of plasmonic semiconductor-based nanocomposites [2,3] that can be promising for mild hyperthermia or photothermal therapy applications. Acknowledgements: The work was supported by OPJAK financed by ESIF and the Czech MEYS (Project No. SENDISO – CZ.02.01.01/00/22_008/0004596) and by the EU Horizon 2020 research and innovation programme under the MSCA-IF, grant agreement No. 897231 (LADENTHER). References: [1] Yu.V. Ryabchikov, “Facile Laser Synthesis of Multimodal Composite Silicon/Gold Nanoparticles with Variable Chemical Composition”, Journal of Nanoparticle Research, 21(4), 85, 2019; [2] Yu.V. Ryabchikov, I. Mirza, M. Flimelová, A. Kana and O. Romanyuk, "Merging of Bi-Modality of Ultrafast Laser Processing: Heating of Si/Au Nanocomposite Solutions with Controlled Chemical Content", Nanomaterials, 14(4), 321, 2024.; [3] Yu.V. Ryabchikov, A. Zaderko, “Green” Fluorescent–Plasmonic Carbon-Based Nanocomposites with Controlled Performance for Mild Laser Hyperthermia”, Photonics, 10, 1229, 2023. ; [4] Yu.V. Ryabchikov, “Multi-modal Laser-Fabricated Nanocomposites with Non-Invasive Tracking Modality and Tuned Plasmonic Properties”, Crystals, 13(9), 1381, 2023.

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Abstract: Recently, there has been great interest in the production of boron nanoparticles, caused by the possibility of their use in composite fuel and in boron neutron capture therapy (BNCT)[1-3]. In this work, Boron nanoparticles are synthesized using laser ablation in isopropanol and subsequent laser fragmentation of the suspension. For this purpose, an ytterbium doped fiber laser was used at wavelength of 1060–1070 nm, pulse repetition rate of 20 kHz, and pulse duration of 200 ns. Laser radiation was focused using an F-Theta lens (F = 204 mm) onto the surface of a sintered boron target located in flow cell. Laser ablation and further laser fragmentation led to the formation of nanoparticles with a size distribution in the range of 7–60 nm (Fig. 1a). Transmission electron microscopy studies confirm the data obtained using a disk centrifuge. Figure 1b shows the morphology of boron nanoparticles. Analysis of the elemental composition of the particle shows that boron NPs have carbon shell. The period of the crystallographic planes of the shell is 0.34 nm, which corresponds to graphitized carbon. Allotropic composition of boron nanoparticles differs from that of the initial Boron target. Thus, boron nanoparticles obtained by laser ablation and fragmentation in isopropanol are promising candidates both for addition to composite fuel and for use in BNCT.

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Abstract: We report femtosecond double pump-probe experiments aiming at a direct observation of carriers dynamics in photoexcited materials (wide bang-gap dielectrics). On the other we have built a new set-up capable to achieve attosecond resolution by probing the laser induced reflectivity change in the VUV domain using ultrashort pulses provided by high order harmonic generation in gases. Preliminary results concerning MgO will be shown.

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Abstract: Our goal is to enhance the laser-glass ablation efficiency by utilizing a dual-seeder laser system, capable of generating ns and ps-pulses simultaneously and tuning their temporal delay. We expect a leading ps-pulse to induce transient effects, which surpress the transmission of IR ns-pulses, that do not reach fluences sufficient for material ablation otherwise. A transmission photodiode signal is observed as a function of the delay between the two pulses the the decreased transmission is observed for trailing ns pulses. Furthermore, single-spot ablation experiments show a significant increase in ablation depth, compares to utilizing only ps-pulses.

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Abstract: This study focuses on observing mid-infrared emissions in the 3-5 µm range using a high-speed camera after laser ablation, targeting blackbody radiation from cooled plasma.

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Abstract: Laser ablation of supersaturated/supercooled liquid has shown promise for controlling crystal nucleation of various materials in a spatiotemporal manner [1-3]. As for the mechanism, previous studies suggest that macroscopic morphological changes (e.g., generation of shockwaves and cavitation bubbles) via laser ablation of liquid plays a crucial role in enforcing crystal nucleation. In particular, laser ablation induced by the focused irradiation with an ultrashort laser pulse can act as a well localized, photomechanical stimulus, which allows for the fine monitoring of crystallization dynamics from targeted places [1-3]. In fact, we recently succeeded in motoring microsecond and micrometer-scale dynamics of ice crystallization that was triggered by the focused irradiation with a single ultrashort laser pulse (e.g., Δt = 5 ps) into supercooled water, which can provide fundamental insights into the primary process of ice crystal nucleation of which understanding important in various scientific and industrial fields (e.g., cryobiology, food processing). These results clearly suggest that the spatiotemporal controllability of the laser ablation-induced crystallization is promising for the detailed investigation of ice crystallization mechanism. To further clarify the laser ablation-induced crystallization dynamics, here we developed a new experimental system with an ultrashort laser (λ = 800 nm, Δt = 100 fs – 10 ns) and a high-speed polarization camera (Figure 1a), which enables us to visualize the orientation structure of crystals. In the experiment, laser pulses were focused into supercooled water through an objective lens (NA = 0.40) from the bottom side of a glass container. The polarized images were captured from the side or bottom of the container. Notably, the high-speed polarization camera could visualize the growth and orientation of individual ice single crystals even when several crystals were formed at the same time, which is crucially challenging in conventional bright-field imaging. We foresee that our laser methods will offer new insights into the crystallization mechanism of ice. References: [1] H. Y. Yoshikawa et al., Chem. Soc. Rev. 43, 2147-2158 (2014); [2] H. Takahashi, H. Y. Yoshikawa et al., Appl. Phys. Exp. 14 045503 (2021); [3] H. Takahashi, Y. Hosokawa, and H. Y. Yoshikawa et al., J. Phys. Chem. Lett. 14, 4394-4402 (2023).

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Abstract: Laser welding has been an established technology in industrial production. Nevertheless, there are many unsolved problems with cracks and pores when welding certain materials such as high-strength aluminum alloys or so-called tailored blanks. New process or exposure strategies are therefore being developed to enable a controlled temperature field within the welding zone and thus deliver better welding results. The aim of this study is to investigate a new type of processing optic that uses bifocal optics to split the laser beam into two partial beams and a fast rotation of these two partial beams. Optimum welding parameters for different materials were determined while varying the rotational speed, laser power and welding speed. The results show that porosity formation and cracks are observed less than with conventional laser welding. At the same time, simulations were created with the FLOW 3D software, which agree very well with the experimental results.

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Abstract: The synthesis of nanostructured glass by the combination of the sol-gel and laser ablation techniques is reported

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Abstract: Optics of two-dimensional materials is at the boundary between classical and quantum physics and chemistry. To ease the design of applications based on 2D materials, we prepared the optical response of a graphene flake on a substrate using ab-initio simulation techniques. The calculations based on advanced molecular dynamics reveal the effect of the ambient temperature on the sample’s absorption spectrum. Results are compared to our absorption spectroscopy measurements and to recent literature.

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Abstract: This research intends to discusses the challenges faced in laser powder bed fusion (PBF) additive manufacturing, particularly regarding periodic undulations leading to defects and structural failure. It highlights the growing interest in external field-assisted laser-based additive manufacturing for its benefits in grain refinement and defect elimination. However, electric field-assisted PBF processes face limitations due to the complex thermophysical properties of the powder bed, leading to defects and repeatability issues. Zhang et al. (2022) examined the Rayleigh instability in PBF, finding that the contact angle affects melt track stability, which in turn is influenced by surface tension and potentially by electric fields. Previous evidence suggests that electric fields can impact surface tension and contact angles. However, existing models like the Young-Lippmann equation do not consider the transient nature of solidification during the process. To address this gap, the research investigates the effects of electric fields on undulations in dual laser-based PBF processes using stainless steel 316L powders and substrates at various parameters. Different electric field signals with varied waveforms and amplitudes are applied during the process, leading to observable changes in melt track undulations. The study finds that electric field characteristics, including waveform, amplitude, and frequency, significantly affect undulations and are directionally dependent. Various materials characterization methods support these findings, suggesting potential applications in defect mitigation and grain refinement through process enhancements.

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Abstract: Studies on surface electrical conductivity induced by ultrashort laser pulses on wide bandgap semiconductors will be reported both in vacuum and in presence of different buffer gases,

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Abstract: Colloidal nanoparticles have received much attention recently. However, understanding their room-temperature reactivity remains an ongoing challenge. The current study aims to investigate the reactive interaction between two different sols of metastable metal monoxides prepared via laser ablation in liquid. Specifically, the research focuses on the properties and behaviour of two colloidal systems, MnO–SiO and Cu2O–SiO, prepared in ethanol and water. Due to their low stability, reactive interactions between colloids are expected. Thus, simple mixing of two different sols at room temperature can lead to the formation of difficult-to-achieve phases, such as silicides and silicates.

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Abstract: Laser ablation in liquids (LAL) has been developed into versatile technique producing various colloidal nanoparticles with applicable properties in e.g. biodetection, luminescence, SERS detection and photocatalysis. Aim of this contribution is present our recent research revealing advantages of LAL for catalytic use consisting in: (i) functionalization of porous surfaces by photocatalytic nanoparticles, (ii) LAL-induced high-pressure structures with enhanced photocatalytic activity, (iii) room temperature reactive interactions between two different sols yielding photocatalytic silicides. (i) One of the typical problems faced in the catalytic applications of colloidal nanoparticles is their instability towards aggregation, which decrease the catalytic properties. A strong effort is devoted to achieving a higher colloidal stability by various stabilizers which are, however, usually not environmentally friendly and such freely moveable nanocatalysts can enter biogeochemical cycles. It is therefore an attractive idea to make use of the adsorption of nanoparticles on rough surfaces. LAL of FeS in water produces FeS-derived colloidal nanoparticles that absorb onto immersed porous ceramic substrates and create solar-light photocatalytic surfaces. The LAL thus offers simple and efficient way for the functionalization of porous surfaces by photocatalytic nanoparticles that precedes aggregation in the liquid phase. (ii) Moreover, LAL-induced FeS-derived nanoparticles contains high-pressure orthorhombic FeS phase which represent so far unreported example of high-pressure structures produced by LAL. High-pressure form of FeS exhibits significantly higher photocatalytic activity compared to its stable phase, which encourage next research of catalytic properties of LAL-induces high-pressure phases. (iii) In spite of advanced research on functional colloidal inorganic nanoparticles and their reactivity, room temperature reactive interactions between two different colloids have remained challenging so far. Simple room temperature mixing of ethanol TiO- and SiO-derived colloids allows the formation of TiSi2, which is the first-ever case of room temperature reactive interactions between two colloidal species. Inclusion of TiSi2 in colloidal mixture significantly enhanced its photocatalytic efficiency for solar-light organics degradation.

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Abstract: This is about the study of the selective laser-induced etching for the micro-hole formation to the glass substrate. As performing the process parameter study of the etching agents or laser parameter conditions, we investigate the factors affecting to the selectivity of glass for acheiving high aspect ratio Through Glass Vias (TGV).

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Abstract: Laser Wakefield Acceleration (LWFA) is an alternative approach to get high-energy particles which are needed for various applications, including generation of secondary radiation, material science, ultrafast X-ray imaging, or radiotherapy. Interaction of spatially and temporally shaped laser pulse with tailored gas jet target is the key for injection and acceleration of electron bunch. We employed hybrid laser ablation processing techniques in fused silica to manufacture specifically designed gas nozzles. The technology provides us flexibility in optimising laser beam shaping and gas target tailoring to generate high-energy electrons with a narrow spectrum using TW-class lasers with limited pulse energy below 100 mJ. Two-stage supersonic gas nozzles combining ionisation injection and acceleration stages were used in the numerical study of the LWFA of electrons. We present Fourier–Bessel particle-in-cell (FBPIC) simulation results from a laser wakefield electron accelerator driven by Gaussian (G) and Bessel-Gauss (BG) laser beams in hydrogen and a mixture of hydrogen–nitrogen gases with different nitrogen concentrations. A TW-class ultrashort 10 fs laser beam is used to study the impact of different nitrogen gas concentrations on the electron beam quality up to an acceleration distance of 1 mm. FBPIC simulations were done in the presence of a two-stage designed gas nozzle. It was found that the highest electron energy is obtained when the nitrogen concentration is 1%, and the electron energy reaches around 150 MeV. Additionally, it is observed that the electron energy decreases with increasing nitrogen concentrations (>1%), and the majority of the accelerated charge exhibits a low-energy Maxwellian spectrum. Experimental validation is ongoing using SYLOS3 lasers at ELI ALPS to verify the simulation results.

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Abstract: When a noble metal is irradiated with a short-pulsed laser in the visible spectrum, sp- and d-electrons are excited into energetically higher free states while the phonons are not directly affected. This process increases the energy content of the electron system and induces non-equilibrium electron distributions including an imbalance in the band occupation. We investigate how this non-equilibrium evolves towards Fermi distributions. We apply full Boltzmann collision integrals for the excitation, electron-electron scattering and electron-phonon scattering. Our approach resolves the distributions in the sp- and d-bands and shows that temperatures are established at different rates. After Fermi-distributions have been established, an occupational non-equilibrium of the considered bands can still persist [1]. Our kinetic calculations confirm that a transient under- or overpopulation of the sp-band can be controlled via the wavelength of the exciting laser. However, we find that both population mismatches can also be reached by varying the laser intensity for a given wavelength. We further investigate how an occupational non-equilibrium affects the electron-phonon coupling. We find a strong dependence of the coupling parameter on the band occupation reflecting features of the band-resolved density of states [2]. Our results demonstrate the importance of non-equilibrium electron distributions on the heating of the crystal lattice and subsequent phase transitions. References: [1] P. Ndione, S. T. Weber, D. O. Gericke and B. Rethfeld, Scientific Reports 12, 4693 (2022). [2] T. Held, S. T. Weber and B. Rethfeld, arXiv:2308.01067 (2023).

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Abstract: The control of laser-induced surface damage on fused silica components, crucial for high-energy laser systems like the Laser MégaJoule (LMJ) in France, is addressed. Surface damage, originating from high-energy photon interaction, initially small, can rapidly expand under successive laser irradiation. CO2 laser processing is effective for mitigation but sensitive to material properties and laser intensity fluctuations, leading to negative effects like surface deformation and debris formation. Collaborative efforts between CEA-CESTA and Institut Fresnel have developed a CO2 laser remediation technique involving micro-ablation of damaged sites. This work focuses on reducing post-processing negative effects, using numerical simulations for insight and guidance in improving processing parameters.

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Abstract: Laser ablation has been developed as a promising technique for photovoltaics (PV) to enhance solar cells' performance and efficiency. Laser ablation is employed for surface texturing and patterning of PVs. For example, it can be used for selective ablation of passivated emitters, anti-reflective coating in inorganic-based solar cells or monolithic interconnections in organic solar cells. In this research, we present laser ablation methods for organic and inorganic PVs and address the challenges of these processes. In inorganic solar cell manufacturing, establishing metal contacts with silicon is crucial for completing the electric circuit, requiring the selective removal of insulating layers (e.g. SiNx)[1]. Pulsed lasers offer a fast, stable, cost-effective, and reliable method for this task. However, concerns about laser-induced damage arise if the SiNx coating does not fully absorb the laser light, potentially causing partial ablation and damage to the underlying emitter, a challenge intensified on textured surfaces. Femtosecond lasers induce nonlinear effects like two-photon absorption, where molecules or atoms absorb two photons simultaneously, leading to an energetically excited state. Utilizing green light at 520 nm also implies UV absorption at half the wavelength (260 nm), with UV intensity increasing quadratically with green light intensity. This phenomenon allows for processing transparent media near the surface without harming underlying layers, provided optimal laser parameters are chosen to minimize thermal damage. Selective laser micromachining is utilized in organic or hybrid solar cells for monolithic interconnection [2]. Thermal diffusion in the irradiated material is significant for long pulse lasers (ns or continuous wave), leading to a large melting zone extending beyond the irradiation zone. In contrast, ultra-short pulse lasers (ps and fs) vaporize material in the irradiation zone before significant heat can be passed on to its surroundings, resulting in clean and high-resolution processing. Three layers (bottom electrode, absorber layer insulation, and front contact) must be individually ablated for monolithic interconnection by laser ablation. Picosecond and femtosecond pulsed laser systems (pulse length 10 ps, wavelength 532 nm, and 200 fs, 520 nm) are available for these processes, ensuring low electrical resistance in the electrical contacts while preserving the solar cell's vulnerable layer structure. References: [1] J. Bonse, G. Mann, J. Krüger, M. Marcinkowski, M. Eberstein, Thin Solid Films. 542 (2013) 420–425. [2] P. Kubis, J. Winter, A. Gavrilova, M. Hennel, S. Schlosser, I. Richter, et. al, Prog. Photovoltaics Res. Appl. 27 (2019) 479–490.

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Abstract: The control of laser-induced transverse crack propagation direction in the volume of material is essential for Bessel beam glass scribing processes. In this paper, we demonstrate the possibility to generate polarization controlled directional transverse cracks in the volume of glass by applying femtosecond laser Bessel beam. We will show that the linear polarization angle corresponded to the crack angle when scribing of a 1 mm-thick glass sample. This allowed us to control the transverse crack direction during laser scribing. We will also present results on scribing with linear polarization orientated in parallel and perpendicular to scribing direction, compare the results with circular polarization for Bessel beam scribing. We will conclude that polarization controlled transverse cracks allowed us to increase the dicing speed and reduce the glass workpiece separation force. Finally, we will demonstrate 4.8 mm glass workpiece dicing with 80 mm/s throughput at single pass regime.

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Abstract: The present study combines a well-defined micro- and nanostructuring of flexible and stretchable polymer substrates using fs-lasers, subsequent surface functionalization and the application of external mechanical strain to investigate the mechano-responsive dynamic wetting of the surface. For this purpose, periodic structures of different size are fabricated on the elastomer surface by fs-laser direct writing and replica casting, respectively. The selective functionalization was realized at different expansion states to locally induce either hydrophilic or hydrophobic sites. The study reveals that the wettability of those polymer substrates can be reversibly adjusted over a wide range between superhydrophilic and superhydrophobic states as function of mechanical deformation. Furthermore, a dynamic switching of the wetting between hydrophilic and hydrophobic behavior under permanent contact with a water droplet was demonstrated.

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Abstract: We present three different approaches on the reduction of droplet incorporation during PLD. The results are demonstrated using boron carbide (B4C) as film material. The various effects of the approaches on the droplets as well as on the film properties are investigated and discussed. We demonstrate that we are able to nearly avoid any droplet incorporation.

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Abstract: We report on the process of femtosecond (fs) laser irradiation and surface structuring of silicon at an ambient pressure ranging from dry vacuum to above atmospheric pressure, which is rarely investigated. For structuring in high pressure, nitrogen gas is pumped into the chamber maintaining the pressure level at ~1.5 bar. The change in the ambient pressure enables the surface structuring process in experimental conditions going from a freely expanding to a redeposited and highly confined nanoparticles cloud, which has a potential role in the formation and evolution of the various periodic surface structures. The irradiation is carried out using a sequence of laser pulses with a duration of ~180 fs at a wavelength of 1030 nm. The surface morphology of the irradiated sample evidences the formation of a variety of subwavelength and supra-wavelength features, including ripples and grooves oriented in direction orthogonal and parallel to the laser polarization, respectively, as well as columnar structures. Our experimental findings allow shedding more light on the influence of the nanoparticle redeposition on the evolution of fine features and supra-wavelength structures, especially the hindering of grooves development below and above the atmospheric pressure, and provide valuable insights on potential formation mechanisms and for further applications. Finally, considerable change in the morphology of the ripples is also observed as a function of the ambient pressure.

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Abstract: Selective Surface Activation Induced by Laser is a technology used for selective copper deposition on various dielectric materials. It has been shown that using this technology copper micro traces under 2 micrometers in width can be formed on glass and PET materials. Metal micro mesh electrodes have great electrical, mechanical, and optical properties and can be used as an alternative for ITO (Indium Tin Oxide).

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Abstract: Glass is one of high-performance materials used in a wide variety of field owing to its high mechanical and electrical insulating properties, chemical and thermal resistance, and transparency. For improving the accuracy and quality of laser processing , measurement of pressure waves leads to evaluation of the state of the processed material and optimization of processing parameters. In this study, we observed the propagation of pressure waves during the laser processing of transparent dielectric materials using pump-probe method. The stress intensity and direction in the material is evaluated by calculating the birefringence of isotropic materials. Figure 1 shows the representative transmission images that measured the processing of amorphas silica glass. Multiple pressure waves were measured, including P and S waves. We report a detailed observation of the stress of pressure waves generated during laser processing.

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Abstract: There is a high interest in process optimisation techniques pursuing higher ablation efficiency. Lasers capable of working in pulse sequence regime, so-called, burst mode are of high interest in this topic. The idea of this work was to investigate two temporal ablation optimisation methods: pulse repetition rate and burst length. These methods are of great interest due to their ability to simultaneously optimise ablation rate (volume per time) and ablation efficiency (volume per energy) with constant focused beam spot size. Ultrashort pulse laser (FemtoLux 30, Ekspla) with a widely tunable repetition rate from 200 kHz to 4 MHz and intra-burst repetition rate of 50 MHz was utilized for ablation of common metals: aluminium, stainless steel and copper. In addition to rapid and efficient material removal, the optimisation resulted in increased ablation quality measured as surface roughness. Therefore, the most important characteristics of the ablation process were enhanced.

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Abstract: The study introduces Laser Ablation as a technique to directly extract metals from volcanic rock, producing nanoparticles.

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Abstract: The laser doping method has recently attracted attention. It potentially bypasses the annealing process of doped wafer for activation of dopant ions owing to the local heating effect of deep. This results in a simpler process flow design. We attempted Sn doping into β-Ga2O3 by the laser doping method with a KrF excimer laser. As a result, we confirm that the depth profile of Sn penetration can be controlled by the fluence, shot number, and repetition frequency.

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Abstract: it is important to achieve high quality and efficient laser welding of pure copper for realization of a carbon-neutral society. we have developed the blue diode laser with a maximum output of 1.5 kW and investigate the phenomena when a pure copper is irradiated by blue diode laser. In a previous study, it was shown that when blue diode laser is used to irradiate a pure copper plate perpendicularly, blue diode laser-induced plume is generated form weld copper surface. There is concern that interference between plumes and laser beam may reduce processing efficiency and cause welding defects. In this study, experiments were conducted to quantify the change in welding efficiency when the plume is air-cut and to quantify the change in plume behavior using spectral analysis.

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Abstract: Nanoparticle-Enhanced Laser Induced Breakdown Spectroscopy (NELIBS) has experienced significant advancements in the last few years, particularly in the analysis of liquid samples. This technique has shown remarkable sensitivity improvements with respect to standard LIBS, with signal enhancements up to two orders of magnitude. The most common nanostructures used for NELIBS are based on Au and Ag nanoparticles. This study presents a preliminary comparison of NELIBS effects using noble metal nanoparticles generated and deposited through wet chemistry and an accurately controlled drop-casting method. Additionally, it examines how the spectroscopic signals of deposited liquid samples are affected by Laser Induced Periodic Surface Structures (LIPSS) manufactured on various substrates (metals, semiconductors, and insulators). To elucidate the relationship between NELIBS enhancements and the mechanisms involved in both types of nanostructured materials, their chemical and physical features are analysed using μ-Raman, Atomic Force Microscopy (AFM), and Scanning Electron Microscopy-Energy Dispersive X-Ray Spectroscopy (SEM-EDS) techniques. The ultimate aim is to use nanoparticle-enhanced and LIPSS-enhanced LIBS, and their improved sensitivity for trace element analysis in biological fluids, for the early diagnosis of neurological conditions such as Autism Spectrum Disorders (ASD).

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Abstract: Live imaging of cell behavior in three-dimensional (3D) micro- and nanoenvironment using microfluidic chips is important to investigate the mechanisms of immune systems or disease progression. A problem of the current microfluidic chips for this application is the refractive-index mismatch between the materials used for chips and culture media containing cells (typically water). We developed the new technique using femtosecond laser to fabricate 3D microfluidic structures in amorphous fluoropolymer CYTOP, because it exhibits not only excellent transparency but also a refractive index (1.334–1.340) very close to that of water (1.333). The fabricated CYTOP 3D microfluidic chips provided excellent ability for high-resolution live imaging of cells.

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Abstract: Despite all the benefits of laser-induced forward transfer (LIFT), such as direct-write and contact-free fabrication, the three-dimensional (3D) shape of the liquid printed structures is determined by the wettability between liquid and substrate. As result, the so printed structures exhibit a fixed geometry in terms of contact angle or aspect ratio. In this work, we try to overcome this limitation by using print-n-release. Based on printing on top of pre-stretched elastomeric substrates, controlled contraction of the substrate is used to enable on-demand selection of the contact angle of drops and the thickness of lines . We obtained microlenses with increased contact angle and decreased focal length. We also fabricated conductive silver tracks with increased aspect ratio.

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Abstract: Treating corneal wounds with corneal pro-regeneration biomaterials is an alternative to transplantation. To allow good vision, treated corneal wounds must be optically clear and their surface must be smooth. Currently, delivery methods for corneal pro-regeneration biomaterials rely on conventional syringe systems, lacking the precision needed to restore the pre-wound corneal topography. I will present a laser-based technology aiming to tackle this challenge. Our approach involves using our lab's drop-on-demand (DOD) bioprinting technology, known as laser-induced side transfer (LIST), as a means to deliver biomaterials to corneal wounds in a precise and personalized manner. We have used LIST to achieve DOD printing of an acellular medium viscosity photo-crosslinkable ink based on Gelatin methacryloyl (GelMa). This formulation supports the growth of human corneal epithelial cells (HCEC) and stromal cells in an in-vitro environment . We established optimal printing conditions and found that printed samples preserve their optical and biomechanical properties compared to control samples, including optical transmission (88±2% (printed) vs 90±1% (control)), diffuse reflectance (1.0±0.3% vs 0.3±0.1%), and storage modulus (1.9±0.1 kPa vs 2.1±0.1 kPa). We utilized optical coherence tomography (OCT) to characterize corneal wounds in cadaveric pig eyes and employed LIST for wound filling. After UV crosslinking, we observed uniform wound filling, resembling the pre-wound corneal topography with the absence of trapped bubbles or off-target material deposition. The sealed wound withstands a pressure of 38±6 mm Hg, 2 times the average intraocular pressure (IOP). In conclusion, our results suggest that LIST printing can efficiently deliver corneal pro-regeneration biomaterials to precisely fill corneal wounds ex-vivo without compromising their optical and biomechanical properties. With further development, this technology could offer an alternative to transplantation for patients who would traditionally be put on corneal transplantation waiting lists.

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Abstract: Femtosecond laser direct write (fs-LDW) is an attractive 3D printing method that allows for high fabrication resolution and nearly arbitrarily free 3D writing capability. Amongst a broad diversity of materials, fs-LDW can utilize protein precursor to fabricate 3D proteinaceous microstructures for various biomimetic and biomedical applications. Here, we present our progress on the fabrication of wireframe 3D microstructures made from protein precursor.

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Abstract: Among different additive manufacturing (AM) technologies, Laser-induced forward transfer (LIFT) has been widely investigated, owing to the eco-friendly rapid processing and the compatibility with a broad range of materials [1]. LIFT has been previously employed for the high throughput printing of Ag NP inks for interconnections [2] and of solder paste for bonding a LED [3]. Here, LIFT has been used (Figure1 (a)) for two applications: the printing of gold patterns onto Si-based substrates and of solder paste patterns. The aim of this work, is to combine LIFT of solder paste and laser soldering process for the digital bonding of micro-components on photonic chips.

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Abstract: An “optical lattice clock” proposed in 2001 benefits from a low quantum-projection noise by simultaneously interrogating many atoms trapped in an optical lattice [1]. About a thousand atoms trapped in the optical lattice allow measuring frequency at 10-18 precision in an average time of a few hours. This superb stability is especially beneficial for chronometric leveling [2,3], which determines a centimeter-level height difference of the clocks located at remote sites by the gravitational redshift. We overview the progress of optical lattice clocks and address recent topics to explore real-world applications of the 18-digit-accurate clocks, including 1) compact optical lattice clocks with a volume of 250 litter developed in collaboration with industry partners, 2) chronometric leveling with transportable clocks over 500 km apart, and 3) our challenge to further improve the clock stability by developing a “longitudinal spectroscopy” that allows continuous interrogation of the clock transition [4] to improve the clock stability. We look ahead to the role of future clocks when networks of high-precision clocks are implemented in society. This work received support from JST-Mirai Program Grant Number JPMJMI18A1, Japan.

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Abstract: We investigate the nonresonant ablation mechanism of multilayer, mixed transition-metal phosphorus trichalcogenides to characterize the mechanism of ablation. Laser machining is used to create nanophotonic devices that take advantage of the high refractive index of these materials.

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Abstract: Two photon polymerization (2PP) is a direct laser writing technique used to fabricate complex micro/nano structures of different light sensitive materials. 2PP is a non-linear optical process that enables the simultaneous absorption of two photons in a photosensitive material known as photoresist. This initiates a polymerization process by activating so called photo-initiators in the photoresist by converting them into radicals and enables the polymerization of the resist locally. The limitations of the existing high numerical aperture focusing lens for two photon polymerisation processes impede scalable high speed production of the scaffolds. This issue is addressed by developing an ultrashort laser scanning, direct write, process with the ability to manufacture the scaffold templates with custom architectures. Two-dimensional (2D) polymer-based scaffolds with the ability of being easily detached from the host substrates are prepared by direct laser writing. An ultra-short laser is used to write the structures. These highly flexible scaffolds can be easily removed from the substrate. The process can produce features down to a few microns in size over large areas -up to 50 mm x 50 mm within minutes. To make the scaffold electrically conductive is also challenging as the metallisation typically requires elevated temperatures (> 600oC) to acquire the appropriate crystallisation to achieve the required electronic conductivity. Such elevated temperatures would destroy the micron-sized features forming the polymer scaffold. We developed low temperature sputter-coated process to add nanometre-thin gold layer on the scaffold structures. These coated non-conductive/highly resistive scaffolds are then annealed with ultra-short laser pulses at controlled and very low fluences. Scaffolds can be rolled or folded with extremely small radii of curvature to produce three dimensional (3D) scaffolds. Mechanical measurements of the scaffold confirm that the effective elastic modulus of the scaffolds can be tuned by the geometric structure which is written into the scaffold. Non-isotropic structures give rise to non-isotropic mechanical properties. Preliminary interaction of the scaffolds with endothelial cells, cardiomyocytes, and clusters of cells known as vascular organoids have been examined and show promising first results. The development of reconfigurable structures can be tailored to suit the mechanical properties and size of the cell or vascular organoids of specific interest. This enables their potential to be deployed as a cardiac patch by minimal invasive surgery.

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Abstract: The use of fast and ultrafast laser pulses is nowadays a well-established technique for micro- and nano-structuring of materials. Direct laser interference patterning (DLIP) with ps and ns pulses has evolved into a promising technique for material micro-structuring thanks to the precise and controlled energy deposition achieved through the interference of two or more coherent laser beams, which allows to fabricate a wide variety of structures in a broad range of materials [1]. When using ultrashort laser pulses, one of the major issues of this technique is the need of a nearly perfect temporal and spatial overlap between the interfering beams. To achieve this, we made use of an imaging set-up by combining commercial or ad-hoc laser-fabricated diffractive optical elements (DOE) with a demagnifying optical system. High-contrast, well-defined excitation profiles with a Gaussian envelope and periods between 5 µm and 650 nm can be achieved employing a commercial Ti:Sa amplified laser (800 nm, 120 fs, 1 mJ) by slightly changing the irradiation configuration. We employed this setup to obtain amorphous or ablative nanostructures in crystalline silicon. The topography of the amorphized regions of the sample shows a strong dependence on the imprinted fringe width. Moreover, we demonstrate the versatility and scalability of this technique by imprinting micro-dots of 1 µm-600 nm diameter and large area (5 mm x 5 mm) nanogratings. The results obtained allow a detailed investigation of the mechanisms responsible for the surface deformation, including melting, Marangoni convection, capillary waves, and resolidification [2]. Furthermore, the technique's exceptional upscaling capacity renders it highly appropriate for industrial applications. [1] L. Mulko, M. Soldera, A.F. Lasagni, Nanophotonics. 11 (2022); [2] M. Alvarez-Alegria, C. Ruiz de Galarreta, and J. Siegel, Laser & Photonics Rev. 17, 2300145 (2023)

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Abstract: In this study, we analyzed texturing features created by a Carbon Dioxide (CO2) laser on decorative soda-lime glass (SLG). The focused laser beam is moved on the glass surface with controlled process parameters i.e., laser output power (P) and beam sweeping speed (V). This process creates typical grooves and cracks at the glass surface[1]. Three features are analyzed in this study i.e., (i) the width of the damaged region, (ii) the depth of the damaged region, and (iii) the number of glass fragment per unit area. Those three features are compared with the process parameters to build a thermo-mechanical model[2]. The goal here is to explore both analytical- and Finite-Element-Method (FEM)-based models to predict decoration features on glass.

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Abstract: The mechanisms responsible for the generation of crystal defects in nanoparticles produced by laser ablation and fragmentation in liquid are discussed based on the results of large-scale atomistic simulations performed for FeNi, Ag, Au, and Cu targets and nanoparticles. The relationships between the defect structures produced in nanoparticles and the synthesis conditions realized during their formation and growth are established. The computational predictions are related to the results of time-resolved optical and X-ray probing of laser-induced processes, as well as ex-situ characterization of nanoparticle structure.

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Abstract: Circularly polarized electromagnetic waves incident on a nanopatterned metasurface, such as produced in thin-film dielectrics or metallic sheets, can experience frequency-dependent filtering effects in reflection and/or transmission geometry. Outcomes from the multi-epoch design optimization procedure – through an evolutionary algorithm and a deep-learning-style approach - are discussed for a frequency-range-neutral comparative consideration suitable for both (nano)printing or ablating of surface patterns.

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Abstract: When subjected to a series of ultrashort laser pulses, an initially smooth surface undergoes a progressive transformation into dissipative structures, empowering it to regulate energy flux and optimize entropy production rates. This phenomenon manifests as the spontaneous emergence of periodic patterns at various scales, with diverse shapes and varying aspect ratios. Consequently, numerous 2D patterns (stripes, labyrinthines, dots, triangles, hexagonal cavities, etc.) have recently been observed at various scales. The theoretical challenge lies in developing an effective model with symmetry breaking, scale invariance, stochasticity, and nonlinear properties to replicate dissipative structures. Describing pattern growth requires nonlinear dynamics under far-from-equilibrium conditions, for which classical equations (Maxwell, Navier-Stokes, Fourier…) demand unknown transient material properties. We have implemented a stochastic Swift-Hohenberg model that replicates hydrodynamic fluctuations near the convective instability threshold, inherent in laser-induced self-organized nanopatterns at the nanoscale. We will show that a deep convolutional network can learn the complexity of patterns, linking model coefficients to experimental parameters to design specific morphologies. The model accurately predicts patterns, identifying laser parameter regions and potentially anticipating physics complexity evolution.

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Abstract: Femtosecond GHz-burst mode laser processing of glasses and silicon has attracted much attention in the last few years showing enhanced ablation rates when well choosing the laser burst parameters [1-2]. Especially, top-down percussion drilling has been demonstrated in different dielectrics with outstanding surface quality of the inner walls and featuring almost cylindrical holes with aspect ratios of up to 150. However, there is a big interest in drilling through vias in glasses (TGV) and semi-conductors, especially in silicon (TSV), as these materials are of extreme interest for applications in microelectronics. In this contribution, we present through via drillings in these materials with a femtosecond laser operating in different GHz-burst and MHz-burst regimes. Our study reveals certain constraints and limits depending on the material characteristics and on the laser parameters. There is a significant difference between the outlet diameter (see Figure 1) that could have been obtained (right) and the one that is actually obtained (left). This observation seems to validate the hypothesis made in [3] that the plasma within the hole plays a crucial role in the drilling process in GHz-burst mode. We show how to overcome these limits and suggest a hypothesis of the drilling process dynamics. Finally, we demonstrate through via drilling results of excellent quality and constant diameter in both glasses and silicon. References: [1] C. Kerse, H. Kalaycoglu, P. Elahi, B. Cetin, D. Kesim, et al., Nature 537, 84–88 (2016). [2] P. Elahi, O. Akçaalan, C. Ertek, K. Eken, F.O. Ilday, et al., Opt. Lett. 43, 535-538 (2018). [3] P. Balage, J. Lopez, G. Bonamis, C. Hönninger, I. Manek-Hönninger, Int. J. Extrem. Manuf. 5, 015002 (2023).

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Abstract: Transparent conductive oxides (TCOs) are materials with low optical absorption in the visible spectrum, which makes them of vital importance in technological applications involving charge transfer and light management like OLED’s, flat panel displays, energy harvesting, photovoltaics, smart windows or transparent heaters [1]. Recently, the feasibility of producing high optical and electrical anisotropies by fs-laser processing in Indium Tin Oxide (ITO) films has been demonstrated [2]. Still, the scarcity and decreasing cost effectiveness of ITO have spurred other TCOs as candidates to take on a much more relevant role in industrial applications. Fluorine-doped Tin Oxide (FTO) has been postulated as a natural substitute for ITO [3]. In this work, we have analyzed electrical and optical anisotropies induced by fs-laser processing of FTO thin films at high repetition rate using a beam-scanning processing approach. Anisotropies are triggered by the formation of Laser Induced Periodic Surface Structures (LIPSS) [4]. The processing conditions (fluence, number of pulses and pulse duration, scan speed…) have a great effect on the degree of anisotropy induced. Through a careful selection of parameters, it is possible to obtain a large conductivity anisotropy between the directions parallel and perpendicular to the LIPSS, with microscopic anisotropy factors (σ_⊥/σ_∥) above ∼10^3 while preserving σ_∥ values within practical limits for device applications.

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Abstract: We present the inscription of Bragg grating reflectors in polypropylene (PP) large diameter (150μm) light-guides using a variety of laser sources including 193nm and 248nm ultraviolet, nanosecond excimer pulse and 514nm, 290fs laser beams, while using phase mask interferometry. An important aspect of this work is the introduction of toluene treatment of PP for reducing its bandgap and simultaneously increasing its photosensitivity at the exposure wavelengths, corresponding to different orders of photon-absorption. The Bragg grating inscription process using different wavelengths is characterized versus the exposure conditions applied. Additional material characterization methods are used for illustrating the underlying photosensitivity mechanism of PP at these wavelengths and intensities/photon densities, while considering the presence of toluene in the soft matrix acting as a plasticizer. Finally, results on the use of the inscribed Bragg grating reflectors in the PP light-guides as strain gauges or temperature probes are exemplified.

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Abstract: We developed the Selective Laser Thermoregulation (SLT) method to heat samples into various shapes by rapidly scanning a laser with a fiber laser and a Galvano scanner. In the previous study, we developed AI, which studied the relationship between temperature distribution and laser irradiation conditions. However, it didn't consider laser movement, which is crucial for SLT. In this study, we focused on AI learning laser movement through reinforcement learning to suggest paths with minimal movements. Reinforcement learning teaches agents optimal actions in an environment. In this study, a laser is an agent moving on the sample surface. Rewards are based on temperature distribution, which is the environment of this study. We compared the Monte Carlo (MC) and Temporal Difference (TD) methods.

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Abstract: A key issue in the use of high-power mid-infrared (Mid-IR) laser sources for a plethora of applications is the investigation of the exciting laser driven physical phenomena taking place in materials coated with dielectric films. Here, we present a theoretical investigation of the ultrafast processes and thermal response upon excitation of two-layered complexes consisting of fused silica thin films placed on silicon substrates with ultrashort pulsed lasers in the Mid-IR spectral regime. We demonstrate that the control of the underlying ultrafast phenomena and the damage threshold (DT) of the substrate are achieved via an appropriate modulation of the thickness of the SiO2 film. It is shown that a decrease of DT by up to ~30% (depending on the pulse width) compared to the absence of coating is feasible emphasising the impact of coatings of a lower refractive index than the substrate. The conditions for patterning the Si substrate due to the excitation of interfacial electromagnetic modes are also discussed. The remarkable predictions can be employed for the development of new optical coatings and components for nonlinear optics and photonics for a large range of Mid-IR laser-based applications.

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Abstract: More than a decade ago, a new area of research was initiated in the field of laser ablation of electrode materials for lithium-ion batteries. While the initial focus was on fundamental studies using nanosecond laser radiation and compact thin-film electrodes (<3 µm) for microbatteries, application-oriented research using composite thick-film electrodes (50-150 µm) with high areal capacity (2-6 mAh/cm2) for mobile applications increasingly became the subject of intense investigations [1]. The development of an efficient research process was made possible by combining laser process technology with battery manufacturing, as well as corresponding analysis at the laboratory level. The control of the electrode porosity, design, and composition via tape casting or laser printing [2], and the short distances to battery assembly, formation, and analysis are crucial factors in this process. Mainly driven by the strong demand for low-cost, reliable, high-energy, and high-capacity batteries for electric vehicles, laser ablation became a promising technology to enable advanced 3D electrode architectures with exceptional electrochemical performances. The implementation of specific 3D electrode designs has been demonstrated to be advantageous in multiple ways, with benefits extending to both battery manufacturing and operation. This facilitates enhanced cost-efficiency in production and improvements in performance, including a fourfold increase in cycle lifetime and optimized rapid charging capabilities. Furthermore, there is evidence that these designs have the potential to contribute to enhanced battery safety, through the reduction of lithium plating [3]. Given the highly functional nature of battery materials and their specific micro- and nano-scale design regarding mechanical and chemical stability, as well as diffusion kinetic properties, the laser-material interaction, the ablation mechanism, and the impact of laser ablation on material level (Figure) and on electrochemical performance on battery level were subjected to detailed analysis. The most prevalent method for electrode structuring is the utilization of ultrafast laser ablation, with the objective of reducing thermally driven material modifications. Recently, high-power ultrafast lasers (>300 W), GHz lasers, and multi-beam processing strategies were developed and employed in roll-to-roll machining to match with processing speeds required for battery production. The upscaling of the 3D battery concept, with capacities of up to 20 Ah, was successfully demonstrated.

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Abstract: Laser-induced graphene (LIG) is an emerging technique for direct writing of 3D porous conductive patterns on selected polymer materials when exposed by a laser beam. An ultrashort laser system can trigger remarkable phenomena in materials due to its extremely short pulse duration. This work reports interesting findings in direct laser writing of conductive patterns during femtosecond laser-polymer interactions. Two different interaction regimes, one with an sp3 carbon dominant phase (regime 1) and one with a sp2 dominant phase (regime 2), both of which are electrically conductive, are observed. During Regime I, ultrashort laser pulses create a highly conductive layer on 50 µm thick flexible polyether ether ketone (PEEK) sheet with strong adhesion to the PEEK sheet; the sheet resistance of laser treated PEEK surface reduced to 9.60 Ω/□ at 270 mJcm-2 laser fluence. In this regime I, for all investigated fluences, we could not obtain the characteristic Raman peaks of graphene. High resolution XPS analysis confirms that PEEK has been modified to carbon phase with sp3 being more dominant than sp2. Even though the sp2 bonding component was not dominant, this regime reported the lowest sheet resistance corresponding to excellent electrical conductivity. At a higher fluence than applied in regime I, the PEEK surface can be converted to sp2 at the expense of surface damage which is less useful for practical applications. Therefore, in regime II, PEEK surface was laser scanned multiple times at a low fluence of 131 mJcm-2 first and then at a fluence of 172 mJcm-2 to convert it into sp2 graphene without causing any damage and affect to adhesion with the underlying PEEK surface. The sp2 dominated phase was confirmed from Raman and XPS in this fluence regime. The corresponding sheet resistance of phase II was 11.53 Ω/□ which corresponds to 4.17 × 103 S/m electrical conductivity. The sheet resistance is slightly higher compared to that obtained in regime I, but here in regime II, a conversion of sp3 to sp2 carbon and an increase in C−C content is a confirmation of laser graphitization of the PEEK film. Additionally, for Regime II, at lower investigated fluence (131 mJcm-2), we collected the ablated nanoparticles. SEM analysis suggests that in ultra-short laser interaction with PEEK, non-melted spherical nanoparticles were emitted during the laser irradiation. The light brown color of emitted nanoparticles is the same as that of PEEK sheet revealing that these nanoparticles were produced in a non-thermal process. It is important to highlight that the first high conductive regime with such high conductivity and dominant sp3 is not observed with longer pulse durations like CO2 laser graphene writing. This reported low fluence femtosecond laser process is highly relevant for direct writing of various conductive structures for electrical and biomedical sensing applications.

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Abstract: Lipid-based nanoparticles (LNPs) can be designed to exhibit the ability to release therapeutic cargo in the presence of a trigger. Here we propose a pulsed laser-triggered release approach based on the interaction of a single laser pulse with gold nanoparticles (AuNPs) contained within engineered LNPs resulting in rapid release of encapsulated therapeutic cargos. We have examined two different approaches to triggered release. In the first approach, a nanosecond laser pulse is employed for the release of the anti-cancer drug Doxorubicin (DOX) from LNPs. The laser is tuned near the plasmon resonance of contained AuNPs leading to the induction of thermal decomposition of the surrounding lipids near the AuNPs, yet, without affecting the integrity of the drug. The second approach consists of laser-triggered liberation of genetic material instead of DOX. In this case, a femtosecond laser pulse is employed to interact with the clustered AuNPs out of the plasmon resonance. Thus, hot spots of field amplification assist the release of the encapsulated substances due to the photochemical decomposition of the lipids. We propose applying triggered gene release by ultrashort laser pulses in ophthalmology, specifically for retina degenerative diseases.

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Abstract: In this paper we report on the successfull preparation and characterization of a nicotinoid insecticide by laser ablation in water.

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Abstract: Laser-assisted selective removal of altered and unwanted crusts and coatings from heritage surfaces is a particularly delicate procedure which urges for refined and reliable monitoring protocols. This gets particularly important in the case of encrustations that show similar physicochemical properties to the underlying authentic surface. Thus, self-limiting laser ablation cannot be guaranteed, as for example the removal of aged varnish films from painted surfaces [1]. Among the different analytical methodologies to follow in real-time the ablation process, the monitoring of acoustic signals produced upon laser-assisted material removal, has been found to be remarkably straightforward and promising [1, 2, 3]. This paper reflects feasibility studies to follow online laser cleaning through the recording of the intrinsically generated acoustic waves during the process and the use of AI algorithms to predict the outcome of the next laser pulse, justifying the decisions taken on the continuation or the suspension of the ablation process. Laser cleaning was undertaken using infrared (1064nm) ns pulses emitted from a QS Nd:YAG laser on model plates. of marble covered with black graffiti films of varying thickness. Irradiation tests with various parameters related to over-, under- and optimum cleaning outcomes are studied on the basis of acoustic monitoring in order to determine the critical AI-indicated thresholds. References: [1] E. Dimitroulaki, G.J. Tserevelakis, K. Melessanaki, G. Zacharakis, P. Pouli, J. of Cultural Heritage, 2023, DOI: 10.1016/j.culher.2023.08.006 [2] G.J. Tserevelakis J.S. Pozo-Antonio, P. Siozos, T. Rivas, P. Pouli, G. Zacharakis, J. of Cultural Heritage, 2019, DOI: 10.1016/j.culher.2018.05.014 [3] A. Papanikolaou, G.J. Tserevelakis, K. Melessanaki, C. Fotakis, G. Zacharakis, P. Pouli, Opto-Electronic Advances, 2020, DOI: 10.29026/oea.2020.190037

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Abstract: The current-voltage (I-V) characteristics of 4H-SiC doped with high concentration of nitrogen formed with silicon nitride (SiNx) film deposited on SiC and excimer laser irradiation were investigated. Until now, evaluation has only been possible at low repetition rates such as 100 Hz. However, we have achieved high-throughput laser doping by enabling high repetition rate irradiation at 4000 Hz using KrF excimer laser manufactured by Gigaphoton Inc., which is necessary for the scale-up of SiC wafers to 8-inch diameters. On the other hand, increasing the repetition rates of the laser raises concerns about the substrate's heat accumulation and melting. In this paper, we will report the repetition rates dependency (100, 1000, 4000 Hz) of I-V characteristics and roughness on the SiC surface after laser irradiation.

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Abstract: We have observed the phenomena of laser ablation in liquid to investigate the particle generation processes. In liquid PDMS, a laser-induced bubble generated on the target surface interestingly retains its shape more than 10 min after laser ablation [1-2]. YAG:Ce is a yellow-emitting phosphor under blue excitation. We used it as a target and observed photoluminescence from YAG:Ce particles generated in single-shot laser ablation of a sintered YAG:Ce in liquid PDMS under 447nm CW laser excitation. Behavior of laser induced bubble was recorded by a high-speed video camera. Photoluminescence was observed in entire bubble area at 60 fps recording rate and 20µs shutter speed. The bubble expanded to several tens of micrometers over a few minutes after irradiation, then a crack appeared in the light emitting bubble surface, and the gas bubble finally floated through the crack while the shell-like emitting region remained on the target. With comparison to our previous shadowgraph observations, we thought that the laser-induced bubble was covered with a thin film of polymerized PDMS with YAG:Ce nanoparticles attached on it and this polymerized bubble surface layer was the reason why the laser-induced bubble remains on the target surface for more than 10 min [2]. Reflections of excitation light from the bubble surface were also captured in the video. To avoid this reflection and make the observations clearer, a filter which can cut the excitation light at 447 nm was placed in front of the camera. It was found that, without the filter, the camera captured not only the reflections but also the scattered light on the bubble surface. Although photoluminescence brightness became much weaker than that without the filter, the time evolution in the photoluminescence area was the same as that without the filter. From the 1st image at 16 ms observed at 60 fps recording rate, it seemed that particles were already attached on the polymerized film on the bubble surface. Therefore, observations at 54 kfps with shutter speed of 18 µs were carried out to elucidate faster stage of bubble generation. In the image indicated as 0.4 µs in Fig.1, path of particles from 0.4 µs after irradiation to 18 µs were observed as photoluminescence tracks. These tracks were observed only inside the bubble, and photoluminescence regions were observed clearly on the entire bubble after several tens of µs. These observations indicate that particles were dispersed by the ablation and adhered to the polymerized film on the bubble surface.

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Abstract: Control over cooper and iodine vacancies and fine-tuning the physical properties through plasma kinetic regulation during the pulsed laser deposition process.

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Abstract: In this work, we discuss Two Photon Polymerized structures made from a combination of the prepolymer poly (ethylene glycol) diacrylate and the photoinitiator Michler’s Ketone using Ti: Sapphire laser operating at 1 kHz repetition frequency. We have studied voxel (polymerized volume) dimensions as a function of laser pulse energy and exposure time (number of pulses). Additionally, we discuss other important parameters like biocompatibility, biodegradation rate, tensile strength and hydrophilicity.

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Abstract: The present study investigates the formation of laser-induced periodic surface structures (LIPSS) on different types of materials and their resulting sliding friction behaviour by means of atomic force microscopy with colloidal probes. The focus is on the comparison of the friction behaviour for different structural sizes, material pairings, surface conditions, as well as applied loads and measurement directions. Friction maps and established contact and friction models are applied for evaluation and interpretation.

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Abstract: Femtosecond lasers revolutionize industrial metal processing, offering exceptional efficiency and precision. However, scaling productivity faces challenges from thermal effects at high laser repetition rates. Our study explores optimizing process efficiency with an industrial-grade femtosecond fiber laser. By fine-tuning parameters, we maximize the material removal rate, achieving record ablation rates for stainless steel and titanium alloy. We demonstrate high-quality deep engraving without intermediate polishing. Utilizing femtosecond pulses below 300 fs, we achieve high-speed drilling of thick metal sheets while minimizing conicity. We show a 50% improvement in processing speed with optimized cutting strategies. Additionally, we highlight the potential of femtosecond lasers in surface polishing, exemplified by polishing dies for coin minting. Our study employs the Jasper X0 fiber laser (Fluence, Poland), with a wavelength of 1030 nm, average power of 20 W, and pulse duration ranging from 0.25 to 20 ps.

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Abstract: Our research is focused on the localized surface plasmon resonance (LSPR) properties of gold nanoparticles (NPs) generated via laser ablation in liquid and their subsequent aggregation induced by halides. We investigated the aggregation dynamics across different parameters such as bromide concentration, temperature variations and different halide salts. By using absorption spectroscopy and electron microscopy characterizations and Finite-Difference Time-Domain simulations we demonstrated that increasing bromide concentrations result in elongated and more intricate aggregates, consequently leading to a red-shift and broadening of the LSPR. These insights will improve the understanding of aggregation phenomena, promoting the advancements in existing applications and inspiring new ones.

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Abstract: Understanding materials’ response to laser excitation with pulse durations below one picosecond is of significant importance for industrial applications. The energy of ultrashort laser pulses in the visible range is mainly absorbed by the electrons, resulting in non-thermal electrons above the Fermi edge, often called “hot electrons”. This non-equilibrium thermalizes to a Fermi-distribution with elevated temperature typically in the following hundreds of femtoseconds. On the picosecond timescale, electrons and phonons relax to a joint temperature. The electron-phonon relaxation process can be described by the well-known two-temperature model (TTM) [1], which, however, neglects the possible influence of non-thermal electrons. Kinetic models, such as full Boltzmann collision integrals [2], can describe the non-thermal stage but with a much higher computational cost. Based on the approach of Tsibidis [3], we have developed an intermediate model that extends the TTM to describe non-thermal electrons [4]. We investigate energy-resolved electron dynamics and the influence of non-thermal electrons on electron-phonon coupling, which have been previously studied using kinetic models [5,6]. Our future plans include the study of non-equilibrium transport effects. We believe that the extended TTM can be a useful tool to capture the influence of non-thermal electrons similar to a full kinetic approach, while maintaining the conceptional and numerical simplicity of the standard TTM. References: [1] S. I. Anisimov, B. L. Kapeliovich and T.L. Perel’man, J. Exp. Theo. Phys. 39, 375 (1974) [2] B. Y. Mueller and B. Rethfeld, Phys. Rev. B 87, 035139 (2013) [3] G. D. Tsibidis, Appl. Phys. A 124, 311 (2018) [4] M. Uehlein, S. T. Weber and B. Rethfeld, Nanomaterials 12, 1655 (2022) [5] C. Seibel, M. Uehlein, T. Held et al., J. Phys. Chem. C 127, 23349 (2023) [6] S. T. Weber and B. Rethfeld, Appl. Surf. Sci. 417, 64 (2017)

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Abstract: In this study, we integrated piezoelectric sensors into the kidney-on-a-chip. A protective layer was deposited on the piezoelectric sensors to shield the electrodes and enhance their lifespan. This protective layer was endowed with nanostructures through 355 nm UV laser processing, rendering the sensor surface hydrophobic and biocompatible . We analysed the laser processing parameters and the hydrophobicity to ensure precise pressure measurement without residue retention. Furthermore, biocompatibility tests (ISO 10993) were conducted to confirm that the sensor surface is non-toxic and does not interfere with biological processes.

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Abstract: In this study, we focused on optimizing the growth of Ho2O3 thin film on an yttrium-stabilized zirconia substrate (YSZ) for the first time. The quality of the grown crystal was characterized using X-ray methods such as X-ray reflectivity (XRR) and reciprocal space mapping (RSM), among others. Additionally, surface morphology was analyzed using atomic force microscopy (AFM). The grown thin film was confirmed to be epitaxial, with a thickness of approximately 33 nm.

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Abstract: Excitation-induced non-thermal melting in silicon, as well as bond-hardening in gold following strong laser irradiation with short pulse durations have been known for several years [1]. Furthermore, several traces of excitation-induced solid-solid phase transitions have been noticed in a variety of materials. Here, we present several approaches to identify and quantify excitation-induced effects changing the bond strength and inducing phase transitions systematically in several semiconductors, metals and alloys obtained from DFT calculations depending on the degree of excitation. These calculation are in line with previous investigations and provide new insights into the change of the bond strength and the induced phase transitions following strong laser excitation.

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Abstract: Transient optical states of highly excited material are investigated. A broadband, spectrally- and time-resolved pump-probe setup records the reflectivity of the irradiated material surface with a temporal resolution of ~10 fs. A better understanding of the processes involved is the basis to control the material changes taking place and thus, for instance, improving the quality of material processing. The experimental results are compared with simulations reviling the importance of the transient values of the reflectivity during the excitation phase.

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Abstract: Nanozymes are nanoscale enzyme mimics. Nanozymes based on noble metals, oxides and carbon based nanostructures have been widely used in different applications including biosensing, cancer therapies and pollution removal. Laser ablation in liquid (LAL) has garnered significant attention in recent years as valuable technique to control the dimension and surface composition of nanomaterials and to prepare polymeric composite system in a simple one pot synthetic strategy. In this work, we have prepared nanocomposites with potential nanozyme capability, i.e. cerium oxide, palladium and silver nanoparticles dispersed in polymer, as collaborative platform with plasmonic, photothermal and photocatalytic properties. The catalytic capability of the active components in the collaborative platform has been tailored with biocompatible and functional polymers such chitosan The chitosan concentration, solution pH and laser parameters (such as wavelenghth, energy and pulse length) have been varied to optimize nanocomposite functional properties. Characterization techniques including Transmission Electron Microscopy (TEM), X-ray Diffraction (XRD), Fourier-Transform Infrared Spectroscopy (FTIR), micro Raman and X-ray Photoelectron Spectroscopy (XPS) were considered to characterize the morphology, size distribution, composition and crystallinity of the fabricated composites. The results demonstrate the feasibility of LAL for the preparation of chitosan/metal composite materials with tailored properties, including improved photocatalytic activity and enhanced antimicrobial activity. These composite materials hold significant potential for applications in wound healing, tissue engineering and environmental remediation.

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Abstract: we demonstrate the laser-induced carbonization on wood-plastic materials using a laser processing technique.

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Abstract: Ripples were directly fabricated on the surface of crystalline Si by femtosecond (fs) laser irradiation both in air and vacuum to investigate the effect of the ambient processing conditions on their surface-enhanced Raman spectroscopy (SERS) response. Ripples produced in air display SERS signals almost an order of magnitude larger than those generated under vacuum, as a consequence of a more effective back-deposition of nanoparticles (NPs) during ablation in air that enhances the surface nano-roughness. SERS efficiency is further enhanced by decoration of the surface ripples with Au NPs thanks to excitation of surface plasmon resonance and creation of concentrated hot spots among the Au NPs. SERS mapping imaging showcases a good uniformity of the rippled substrates and demonstrate a great difference in the signal intensity between ripples generated in air and vacuum. A high Raman enhancement factors of 109 is achieved that results in good agreement with the prediction of finite-elements method simulation of the electric field enhancement. Our observations confirm the feasibility of the method and the role of the processing ambient for the fs direct laser fabrication of SERS substrates.

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Abstract: Τhe impact of the excited electromagnetic surface modes in an investigation of the formation of laser-induced periodic surface structures (LIPSS) is analyzed. It is demonstrated that the electromagnetic origin of low spatial-frequency LIPSS (LSFL) is the frequency detuning between propagating and localized modes due to their coupling/hybridization. The influence of the pattern profile, inhomogeneity, and material type on the coupling strength, electric-field spatial distribution, and associated near-field scattering are highlighted. Exploiting the potential of the approach, evidence of a universal manifestation of LSFLs is provided irrespective of the material predicting and validating the experimentally-proven lower limit of LSFL periodicity (i.e., λL/2, where λL stands for the laser wavelength). The analysis of the electromagnetic modes predicts that the periodicity of LSFL is practically unaffected by the laser fluence, while a suppression of LSFL at high excitation levels or large number of pulses is also predicted. It is also shown that plasmonic-active materials are not necessary for LSFL formation perpendicular to polarization. Toward these directions, an important generic metric, namely the resonance quality factor, is inserted. The approach can, thus, serve as a guide for controlling laser-induced surface topography.

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Abstract: Over the past three decades, significant research and development investments from various sectors including SMEs, academia, and national laboratories have pushed the advancement of battery technology, catering to the needs of portable electronics, devices, and hybrid electric vehicles. This remarkable technological evolution hinges on lithium-ion intercalation chemistry, renowned for its remarkable versatility. However, as the lithium-ion intercalation approach is reaching its theoretical limits, there arises a pressing need for innovative methods to store more energy in batteries based on them. In this study, we propose a novel approach employing (a) laser-induced periodic surface structure (LIPSS) patterning under ambient conditions, and (b) coating with an artificial solid-state electrolyte (aSEI) to fabricate a stainless-steel (SS) lithium-less Li metal electrode (L3ME). This electrode shows the capability to reversibly plate and strip lithium for hundreds of cycles in an aprotic galvanostatic cell. The LIPSS technique facilitates the creation of regular micrometer-long ripples on the surface of SS, with periods falling within the 150-250 nm range. Concurrently, aSEI deposition induces the formation of a smooth surface morphology through the homogeneous dispersion of a polymeric-inorganic composite film. An array of LIPSS patterning conditions and aSEI compositions have been thoroughly analysed. Optimal L3ME materials comprise SS thin foils featuring a mesostructured surface pattern characterized by a regular distribution of ripples composed of Fe and Fe2O3. This structured surface pattern is hidden beneath a uniform and smooth polyethylene oxide-LiNO3 composite film. Notably, L3ME electrodes exhibit superior performance in aprotic lithium cells, accommodating fully reversible metallic Li stripping and deposition with coulombic efficiencies of 100% over hundreds of cycles. Comparative assessments against bare copper electrodes and other lithium-less substrates underscore the unique synergistic effects of LIPSS and aSEI, enhancing plating and stripping reversibility by selectively impeding electrochemical lithium dissolution. Acknowledgements: This research has been partially performed within the framework of the project funded by the European Union - NextGenerationEU under the National Recovery and Resilience Plan (NRRP), Mission 04 Component 2 Investment 3.1 | Project Code: IR0000027 - CUP: B33C22000710006 - iENTRANCE@ENL: Infrastructure for Energy TRAnsition aNd Circular Economy @ EuroNanoLab

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Abstract: We unveil a novel application of Neural Networks (NNs), to recover information from optical holograms, subjected to distortion within a highly nonlinear and turbulent medium. High power laser holograms transmitted through an ethanol-filled cuvette, suffer from laser beam filamentation and thermal turbulence, resulting to totally scrambled amplitude and phase speckle patterns. Retrieval of the initial information, from these speckle patterns, is impossible through physical modeling of this nonlinear and chaotic system. Yet, we demonstrate that NNs trained on experimental data, provide a robust way to fully recover the original hologram images. Remarkably, our approach demonstrates the ability to decode intricate spatial information, without prior knowledge of pulse conditions or complex nonlinear events, marking a significant advancement in information retrieval from chaotic media.

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Abstract: Hydrodynamic micron-deformation is one of the heart studies from extreme ultraviolet to X-ray generation. Generally, liquids are deformed by a jetting nozzle sharpness and, electric- and magnetic-force, however these forces are relatively small and static. Recently, Laser ablation method is successfully employed for extreme ultraviolet generation of semiconductor lithography machines. However, the dynamics of liquid deformation in the micro-spatial space occurs the time regime from several ten nanosecond to several hundred nanosecond, and traditional pump probe method is equipped with the delay line, which is typical range from femtosecond to picosecond. In this research, we report that the pump-probe method, which has a fiber delay with a cable length of 100-meter, is developed and imaged the micro liquid deformation with a femtosecond resolution and a several hundred delay time.

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Abstract: We will report experimental results on the deposition of metallic nanoparticle-assembled film by femtosecond laser ablation in air. Besides previous works on pulsed laser deposition at atmospheric pressure, our investigation regards the use of high repetition rate and the possibility to use a substrate held at room temperature or heated up to several hundred degrees Celsius. Poster presentation preferred.

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Abstract: Highly polymorphic iron and cobalt sulfides are attractive materials due to their unique electronic, optical, magnetic, mechanical and catalytic properties. Bimetallic Fe-Co sulfides are desirable materials due to their superior catalytic properties compared to their monometallic counterparts. A methods of pulsed laser deposition of equimolar FeS2+CoS2 target onto Ta substrate and the route of precipitation from Na2S.6H2O, CoCl2.6H2O, and FeCl2.4H2O in a sodium metasilicate environment are presented. Thermodynamically non-equilibrium (laser ablation) and equilibrium (precipitation) processes provide different approaches to the preparation of bimetallic sulfides. The resulting materials were analysed by scanning and transmission electron microscopy, EDS, X-ray and electron diffraction and Raman spectroscopy. These complementary analyses revealed that the film on Ta consists of a bimetallic sulphide of cobaltpentlandite (FeCo8S8) and a smythite phase (Fe3S4). In contrast to the laser ablation process, the precipitation method leads to the formation of iron sulphide nanoparticles coated by a SiO2 layer, whereas iron and cobalt sulphides are completely converted to oxides, e.g. wüestite FeO, upon removal of the stabilising SiO2 coating by HF.

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Abstract: High quality ripple-structures on silicon (Si) surface were directly fabricated by femtosecond (fs) laser irradiation in air developing large-area, low-cost substrates for surface-enhanced Raman spectroscopy (SERS). Rippled subwavelength structures exhibit a significant SERS response thanks to both an electromagnetic (EM) field enhancement originating from the narrow gaps between adjacent ripples and a plasmonic coupling among the Au nanoparticles (NPs), where the concentrated hot spots tend to occur. SERS mapping shows a good uniformity, with ±8% deviation over a 15×20 mm2 area and reveals a large disparity in the signal strength with respect to that displayed by the micron-sized surface structures produced at larger laser fluence, for which a two order of magnitude lower SERS signal is achieved. The SERS rippled substrates are able to detect a Raman analyte at a minimal concentration of 10-12 M for RhB and 10-11 M for MBA, respectively. Furthermore, a good agreement is attained between the values of the Raman enhancement factors (EFs) obtained experimentally and by simulations through Finite Elements Method calculations. Our findings demonstrate that the proposed approach can provide a feasible and efficient method for the fabrication of SERS substrates with high Raman detection capability of analytes in trace amounts.

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Abstract: Inorganic halide perovskites, such as CsPbBr3, have extensively been investigated the recent years, as an emerging new generation class of materials. Owing to their novel optoelectronic properties [1] such as high carrier mobility, excellent photoluminescence quantum yield and tunable band gap, they have gained enormous interest for their potential use in a wide range of applications, such as in light-emitting diodes [2], photodetectors, photocatalysis [3] and more recently in sensing technologies [4]. Focusing on their fabrication, the synthesis of halide perovskite nanocrystals based on solution methods [5] is widely reported, the growth of the material in the form of thin film is much less explored. In this work we report on the fabrication and characterization of cesium lead bromide thin films by applying a well-established physical vapor deposition technique, Pulsed Laser Deposition (PLD) [5]. As laser source, a KrF Excimer laser was used (λ=248 nm, τ = 15 ns). The ablated material was collected on silicon and quartz substrates. Particular emphasis was placed on the investigation of the effect of substrate temperature (ranging from room temperature to 350 °C), exploring two different laser energy densities (0.6 and 1.2 J/cm2), on films properties. The as-synthesized cesium lead bromide films, were fully characterized in terms of their morphological, structural and optical properties by Field Emission Scanning Electron Microscopy (FE-SEM), profilometry, X-Ray Diffraction (XRD), UV-Vis and Photoluminescence (PL) Spectroscopy.

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Abstract: Femtosecond laser irradiation is capable to induce precise alterations in the physical properties of dielectrics, enabling the fabrication of 3D nanostructures with unprecedented resolution. Recent observations have unveiled laser-induced super-dense phases within the bulk of materials such as sapphire and quartz, sparking interest in understanding the underlying mechanisms to refine this process. We performed Molecular Dynamics simulations of amorphous silica, subjected to various thermodynamic conditions attainable by femtosecond laser irradiation, aiming to elucidate and harness the phenomena of high local densification. We demonstrated that applying a pressure of 100 GPa, followed by an ultrafast pressure relaxation, yields a stable 50% density increase. In addition to pressure-induced densification, we explored the density anomaly phenomenon, wherein silica's density increases with temperature post-melting point, and the possibility to replicate it by ultrafast-laser excitation. Our findings shed light on the mechanisms of laser-induced densification, presenting a promising pathway to engineer silica-based materials with tailored densities and properties.

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Abstract: In recent years, plasmonic nanostructures have garnered significant interest from researchers due to their promising applications in various fields, including plasmonic nanolasing, surface-enhanced Raman scattering (SERS), and optical label-free biosensing. The key behind this interest lies in utilizing the plasmonic effect, also known as plasmonic resonance. Traditionally, plasmonic nanostructures are manufactured using electron or ion-beam lithography techniques, however, these methods face challenges such as limited scalability, the need for expensive equipment, and specialized facilities. Recent advancements in laser-direct writing for plasmonic structure fabrication have addressed these limitations, making the production of plasmonic gratings more cost-effective and, simultaneously, more appealing for both new research and the commercialization process.

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Abstract: In the process of laser ablation, downstream optical components often exhibit a pattern of deposited particles that resembles optical gratings. This indicates that the material removal and deposition patterns during laser ablation can affect the performance and accuracy of optical systems, presenting a scientific issue worthy of in-depth study.

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Abstract: We investigated the laser induced periodic surface structures (LIPSS) formed on a stainless steel (SUS430) with a femtosecond pulsed laser (pulse width 150 fs, wavelength of 515 nm, repetition rate of 0.5–5 kHz, and laser fluence of 0.1–0.3 J/cm2) and we investigated the relationship between the LIPSS and the bacterial effect of the surface and compared LIPSS formed by nanosecond pulsed laser.

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Abstract: The ultrashort pulse laser has widely been used for the micro-drilling of metals in many industrial applications such as aerospace, biomedical, and semiconductors. Precise shape and size of the micro holes were mostly required for cooling of the gas turbine blades in the aerospace industry [1]. To improve the cooling effectiveness, different shaped micro holes have been drilled with an acute angle ranging from 15 to 35 degrees on the turbine blade [2]. When the ultrashort pulse laser beam incident on the target surface with an angle, the optical properties of the material changes with angle of incidence. Further, the polarization effect plays a significant role in the laser intensity distribution on the target surface [3-4]. Therefore, detailed investigations of the ultrashort pulse laser material interaction with the angle of incidence are highly required. In the present work, the ultrashort pulse laser material interaction on an inclined surface is investigated based on a 2D two-temperature model (ttm) with an angle of incidence. The numerical simulations are carried out by using the finite element-based COMSOL Multiphysics software. The influence of optical properties with the angle of incidence on the inclined surface is explored by considering the polarization effect. The electron and lattice temperature distribution are predicted from the simulation results for different laser fluences. Further, the ultrashort pulse laser ablated crater profiles are predicted using the moving mesh approach for different angles of incidence. The present simulation approach is useful for the selection of laser process parameters in the ultrashort laser-material interaction with an angle of incidence.

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Abstract: In this work, we explore the assisted absorption mechanisms and potential applications of femtosecond laser-irradiated dielectrics doped with Au ions. Different from recent studies on shallow implantation with keV ion, we employ deep implantation at by using swift heavy ions (Au at 1.8 MeV [2]). We investigate the unique properties of the so-prepared nanocomposite materials as well as the local changes induced by subsequent femtosecond laser processing (800 nm, 130 fs, and 1 kHz). First, we demonstrate the existence of an embedded gold NP layer centered at 480 nm depth. This layer is crucial for energy deposition and triggers ablation of the entire top glass layer, forming deep and morphologically flat craters. This result can be understood by considering a spallative ablation process localized at the NP-glass interface, which can enable ablation depth control by selectively controlling the implantation depth. Second, due to the deep-embedded Au NPs layer the sample shows both a plasmonic and interferencial behaviour, which has a strong effect on the sample color. This optoplasmonic response can be tuned by the laser conditions , generating vivid blue-shifted colors by surface swelling and red-shifted colors by multi-shot irradiation at moderate fluences.

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Abstract: Strain influences the band structure and optical properties of semiconductors. In the case of GaAs quantum dots (QD), which can serve as sources of entangled photons, the specific introduction of strain can influence the emission characteristics in a way to optimize the entangled state by compensation of the fine structure splitting. Since the QD emitters are operated at cryogenic temperatures, an actuator platform is required that delivers strain values high enough to achieve full compensation under these conditions. Single crystal PMN-PT shows a giant piezoelectric response and is therefore one of the most promising materials for this application. The possibility of using this material with high innovation potential depends essentially on the extent to which it can be processed with the necessary precision and quality. The manufacturing options for this very fragile and temperature-sensitive material are severely limited and have disadvantages like the long processing time, the introduction of too much damage to the substrate material or the limited flexibility. We show the completely laser-based realization of different actuator designs and their application for entangled photon quantum emitters. The actuators enable a full control of the in-plane strain tensor in a semiconductor nanomembrane with GaAs QDs, bonded directly on the actuator surface [1-4]. The experiments were done using a femtosecond laser with a pulse duration of 350 fs. The laser was operated at its second or third harmonic wavelength of 520 nm and 345 nm, respectively, depending on the actuator design.

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Abstract: Femtosecond lasers offer precise and efficient processing for dielectric materials in industrial applications. To optimize efficiency, one can use GHz burst technology to achieve optimal fluence values. The study investigates different burst configurations with the FemtoLux 30 laser system to enhance processing efficiency.

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Abstract: During this talk, I want to present experimental results on the wavelength dependence of the ablation threshold of several semiconductors. More specifically, I will show the behavior of the ablation threshold at wavelengths corresponding to photon energies in the range around the N to N+1 photon absorption transition for these materials.

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Abstract: Study of the calculation of the activation energy of zinc and tin metallic films, using copper resistive heater and femtosecond laser. The results are compared to the studies made using other characterisation techniques.

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Abstract: We developed a multi-modal Artificial Intelligence (AI) that predicts functions and properties (such as wettability and light transmittance) of glass from laser process parameters in surface processing. Using generative AI, we have developed a multimodal AI consisting of two stages that generates a surface profile from the laser processing parameters and predicts the wettability and transmittance of glass from the AI generated surface shape. We will present the results of verifying whether it is possible to improve prediction accuracy by adopting a multi-modal AI model composed of multiple stages instead of the single AI architecture.

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Abstract: We present a systematic investigation of the above multiscale physical processes by evaluating the role of the laser parameters in the features of the induced morphologies. The modelling based on these mechanisms is validated in the experimental observations. The developed self-organised microrod arrays are important for the development of structured surfaces for microbiology, catalysis and biomedical applications.

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Abstract: This study using two pulsed laser light sources (i.e. 1064 nm and 532 nm pulsed laser) to conduct laser fragmentation in liquid analysis on copper target with a purity of 99.99 wt%. Due to the energy gap values of the two laser light sources are different, to obtain the interaction relationship between the laser and the material, light detectors and spectrometers are used to monitor the key signals of each process during the fragmentation process. The basis for parameter adjustment and optimization in the interaction process of induced and reduced preparation of nanoparticle composite materials is used to construct a theoretical model of the laser/material interaction process of nanomaterials under liquid phase conditions.

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Abstract: A high performance gas sensor is fabricated using high power impulse magnetron sputtering (HiPIMS) process with ZnO as the sensing material which is deposited on micro electro mechanical systems (MEMS) device. The morphology and nanostructure properties of ZnO were tested with XRD, SEM, EDS and XPS. Gas-sensing films operate at different powers and times using laser annealing. Various gas sensing properties will be tested in micro electro mechanical systems (MEMS) device.

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Abstract: Nanophotonic structures are used to achieve desired optical properties, such as strong light-matter interactions, enhanced light absorption, or efficient light emission. These structures are usually created through time-consuming and costly methods, such as electron beam lithography or focused ion beam milling. Nanophotonic structures can be formed using a laser-based technique, which reduces production costs due to its single-step, large-scale, chemical-free processing without the need for specialized vacuum equipment. This makes these structures more appealing for commercial applications. This presentation provides a brief introduction to the field of plasmonics, including the fabrication of nanophotonic structures using direct laser writing technique and their potential practical applications.

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Abstract: Here we present findings on laser direct writing via Multiphoton Lithography (MPL) of non-photosensitized SZ2080™, utilizing a range of wavelengths alongside varying pulse durations and repetition rates. This precise and genuinely three-dimensional printing technique, is confirmed through experimentation, without reliance on photoinitiators and with the application of different wavelengths.

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Abstract: Fabrication of 3D bio inspired hierarchical Materials with enhanced mechanical properties via two photon polymerization (2PP).

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Abstract: Multiphoton lithography is an additive manufacturing technology that can generate 3D structures. The beam's high intensity can cause the absorption of two or more photons within the focal volume of a photocurable material, leading the material to crosslink locally. Auxetic materials are materials with a negative Poisson ratio that possess exceptional mechanical characteristics and have been highlighted as potential candidates for the fabrication of porous scaffolds. The objective of this work is to investigate the auxetic effect on the differentiation of neural stem cells.

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Abstract: The development of biomimetic environments is key in the field of Tissue Engineering (TE), which aims to restore the function of damaged tissues by combining cell cultures, scaffolds and growth factors towards the creation of functional grafts that will be surgically inserted into the body. One of the major tissues that has attracted the interest of TE is the nervous tissue (central and peripheral) due to the intrinsic inability of the central sub-system to self regenerate, making it the most challenging tissue to recover in TE and commanding strategies and solutions to be developed on demand. Here, we showcase the development of two in vitro biomimetic environments for the creation of in vitro experimental models to form the basis of studying neurodegenerative diseases and developing strategies to counter them. The basic concept of TE was combined with commonly used methodologies that have been proven to enhance cell functions and responses such as co-culturing environments and electrical stimulation of neural stem cells. The combined effects of the provided stimuli alongside the scaffold topographies highly influenced cell responses and fate and played a vital role towards the development of the aforementioned biomimetic environments and the creation of functional neuronal networks in vitro.

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Abstract: Over the recent years a highly interdisciplinary field of research has been developed concerning the design, the synthesis and the fabrication of bioinspired materials and surfaces. Natural biopolymers offer an excellent environment for tissue regeneration, with the added capability of forming foam-like scaffolds when irradiated with UV laser light, imitating the natural conditions of cell adhesion (biomimetic scaffolds). Chitosan, a pH-sensitive biodegradable component, with controllable rate of drug release and an excellent tablet binder, is blended with mastic gum known for its antimicrobial, antibacterial, antioxidant activity, with cell healing properties and excellent mechanical behavior. Laser biopolymer processing offers the potential for diverse scaffold fabrication, relying on the unique characteristics of laser light [1], [2]. In the present study, we report on the morphological features of the laser induced structures and their dependence on the irradiation parameters. Furthermore the effect of the different fabricated topographies was studied over cell response.

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Abstract: In this work we exploit the capabilities of multiphoton lithography, fabricating planar asymmetrically arranged SRRs for harvesting the energy in IR spectrum that is emitted from photovoltaic devices.

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Abstract: Multi-photon lithography is a powerful 3D printing technique which enables the direct writing of computer-designed structures within the volume of a photosensitive material. Here, we present different designs of micro-optical elements fabricated either on glass substrates or directly onto the end-face of optical fibers.

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Abstract: This work demonstrates the effectiveness of advanced multi-photon lithography, enabling the high-fidelity printing of micro-optics. These micro-optics, whether they are micro-spheres that enhance the lateral resolution of optical microscopes beyond conventional optics limits or multi-level diffractive optical elements, can be fabricated on challenging surfaces, making them applicable in real-world scenarios.

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Abstract: We present a novel formulation of organically modified ceramics materials, with improved Laser Induced Damage Threshold performance, compared to other materials used for micro-optical elements fabrication using multi-photon lithography (MPL). These materials were used for the fabrication and characterization of lenses and axicons on glass substrates and on optical fiber tips by MPL

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Abstract: This study unveils the realization of three-dimensional structures coated with titanium nanorods for enhancing photocatalytic performance by increasing the active surface area.

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Abstract: Bioprinting technologies represent a transformative approach to tissue engineering, aiming to fabricate biomimetic constructs that closely resemble natural tissue structures through a layer-by-layer biomaterial deposition. Our laboratory has pioneered a laser-assisted bioprinting technique known as LIST. LIST employs low-energy nanosecond (ns) laser pulses (532 nm) pulses to transfer cell-laden inks from a glass microcapillary to a receiving substrate with high precision. Here, I will present modeling results and experimental data on a new fiber-based implementation of LIST that eliminates the use of bulky beam delivery optics, thus enabling miniaturization of the printing head and integration with hand-held systems. We sought to understand how key process conditions affect printability. Model inks (1-10 cP) were printed using the fiber-based system employing a glass capillary with a 200 µm laser-machined opening acting as a nozzle. Jet dynamics were acquired using fast imaging. A model for the simulating the printing process was built in COMSOL, accounting for thermocavitation and fluid dynamics. We have validated our model using experimentally measured jetting parameters such as pinch-off time (140-310 µs), jet velocity (2-16 m/s), and deposited volume (0.5-12 nl). We further explore how the model can be used to predict the printability of non-validated formulations as well as to optimize the printing architecture, including the capillary and opening size. Our findings suggest that fiber-based LIST has uncompromised printing performance compared to the bulky free-space system, while allowing easy integration with robotic and/or hand-held systems. The system is of particular interest for in-situ bioprinting applications, such as wound repair.

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Abstract: Bone-related disorders affect millions of people worldwide, necessitating advanced solutions for bone tissue engineering and regeneration. Traditional 3D printing methods struggle to replicate the complex trabecular structure and composition of cancellous bone, highlighting the need for innovative approaches. The composition of bone includes an organic phase (collagen/cells), an inorganic phase (hydroxyapatite/metals) and water. The purpose of this study is to fabricate bone-like scaffolds with the desired structure and composition to promote bone regeneration. Gelatin methacrylate -a natural biodegradable material derived from hydrolyzed collagen- metal ions and hydroxyapatite are used in this study, for the resemblance of organic and inorganic phase. Multiphoton lithography and more specifically 2PP is employed to fabricate intricate scaffolds followed by a hydrogel infusion process for metal ion incorporation and a mineralization procedure for the formation of hydroxyapatite. Biocompatible GelMA scaffolds successfully fabricated with various complex structures (e.g., square lattices, Triply Periodic Minimal Surface - TPMS structures) using FDA-approved photosensitive molecules (Eosin Y/Bengal Rose) and effectively infused with metal ions (zinc/iron), while hydroxyapatite formation was achieved on both the surface and within the hydrogel scaffolds. This research demonstrates the feasibility of using multiphoton lithography for the creation of complicated hydrogel scaffolds, while the post-fabrication modification provides several desirable characteristics such as antimicrobial properties and osteogenesis, ideal for bone regeneration applications.

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Abstract: Pathway for a large area (more than 4 inch wafer) solar cell patterning for light trapping using photonic crystals (PhCs) texture is demonstrated using femtosecond Bessel beam on Si solar cells (2 x 2 cm2). This PhC light trapping surpasses the Lambertian (ray optics) light trapping used so far and opens possibility of approaching 30% light-to-electricity conversion efficiencies.

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Abstract: Additive manufacturing is a major key technology for most of the current industry developers because of the great advantages it offers for the fabrication of complex 3D structures. Talking about the photonic industry, great incomes have arrived in the last decades thanks to the evolution of ultrafast lasers, and so, its applications on small optical components. That is the case of the work developed within the FABulous project, that aims to develop new manufacturing processes for industrial-scale applications, creating novel metasurfaces that enhance the efficiency and performance of optical products. The work presented here shows some of the results obtained by a two-photon polymerization (2pp) process where a spatial light modulator (SLM) device is used to create arrays of identical 3D structures in just a few milliseconds. The fabrication of features with lateral sizes well below the micron range using a combined phase-amplitude laser beam modulation is introduced and discussed. Moreover, the use of different scanning strategies to make use of the parallelization of 2PP through the use of SLM displays as a function of the nanofeature design will be analyzed, showing its great advantages in terms of enhanced process productivity without affecting the resolution of the nanostructures to be produced. Thus, the lates results in terms of improved resolution and productivity obtained within the frame of the FABulous project will be presented, showing how the developed technology can boost the fabrication of 3D nano- and metasurfaces with unprecedent productivities.

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Abstract: Efficient integration of novel ultracompact light sources and photodetectors is paramount for next-generation energy-efficient photonic integrated systems such as neuromorphic computational chips. However, integration of these photonic devices in emitter-receiver communication circuits remains challenging. 3D waveguides have been proposed as promising devices for on-chip photonic interconnects. Here we report versatile long, aircladded suspended 3D polymer waveguides (OrmoCore), reaching 900 μm in length without intermediate mechanical support structures, suitable for on-chip out-of-plane light routing. This is achieved by applying a zig-zag voxel trajectory to the TPP microprinting. The waveguides show optical transmission losses of 1.93 dB/mm at λ=635 nm, and of 3.71 dB/mm at λ = 830 nm in range of GaAs-based microLEDs spectral emission. Crossing waveguides are arranged in a 3D superposition along the perpendicular direction to the substrate allowing for more complex interconnect networks. Furthermore, we devise an alignment method using the same laser source for sample imaging and fabrication, allowing accurate TPP 3D printing on microstructured chips. As a proof of concept, we optically interconnect two GaAs-based microLEDs via a microprinted 3D polymer waveguide. Such interconnected systems can serve as building blocks for future complex integrated heterogeneous photonic networks.

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Abstract: We focused a terahertz （THz）free electron laser and irradiated the phase change recording material Ge2Sb2Te2 (GST) with a fluence of 35 J/cm2. Laser-induced periodic surface structures (LIPSS) Two patterns of LIPSS were generated, parallel and perpendicular to the laser polarization direction. The spacing corresponds to 1/4 wavelength and 1/18 wavelength, respectively. This result is the first time one laser source is used in the THz region to form two types of LIPSS on one sample. We have provided experimental results that are effective on the generation principle of LIPSS in the THz region.

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Abstract: Femtosecond Pulsed Laser Deposition (fs-PLD) is exploited as a versatile and flexible technique to produce nanoparticle-assembled films and nanofoams, with great flexibility in material choice and composition, together with morphology control down to the nanoscale. Among the many different applications of low-density nanofoams, target production for high-intensity laser-matter interaction experiments is mentioned to illustrate the main advantages of the fs-PLD technique.

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Abstract: Ultrafast laser machining is featured for its ultrahigh precision and flexibility. This research explores the possibility of large area patterning of Silicon Nitride nano thickness membranes using ultrafast lasers. The material ablation with various laser pulse energy and number of pulses are studied, revealing the morphological and chemical changes. The key challenge is the stress concentration during laser cutting, and a "low stress" laser machining method is proposed to avoid this issue. The method is justified by finite element simulation, and is proved to be feasible and reliable in actual fabrications of high quality factor membrane devices with various designs.

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Abstract: In the Selective Laser Thermoregulation system, a laser is scanned at high speed to heat the target surface. To control heat distribution actively in this system, we developed a feedback system that scans the light to the lowest temperature point. This feedback system heats the surface by scanning the irradiation point to the lowest temperature point. This feedback system repeats this movement because the unheated area cools while the light is moving. We calculated numerically the temperature distribution when this movement is repeated. As a result, we were able to reduce the difference between the maximum and minimum temperatures in the temperature distribution compared to the conventional SLT system. We considered that this feedback system can achieve a more uniform temperature distribution.

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Abstract: In this paper, a Slit coupled Laser induced breakdown spectroscopy (s-LIBS) technique combined with machine learning algorithm is proposed to measure the soil nutrients (Macro nutrients: N, P, K, Ca, Mg, S and Micro nutrients: Fe, Zn, B, Cu, Mn) from a stand-off distance (0.6 m to 2 m).

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Abstract: The near-surface implantation of Mn and N ions was used as a probe to investigate the formation of laser-induced periodic surface structures (LIPSS) on stainless steel. The elements deposited at different material depths serve as reference layers of defined thickness, which act as a kind of coordinate system. Using different analysis techniques, the approach enables an evaluation of the selective material removal during the formation process and the determination of the position of peaks and valleys of the LIPSS topography in relation to the initial surface before fs-laser irradiation.