This research develops diamond-reinforced metal matrix composites (MMCs) for advanced thermal management using laser powder bed fusion (LPBF) and femtosecond (fs) laser polishing. Cu alloyed with 1.5 wt.% Al achieved >98% density at low energy density (222 J/mm³), enabling efficient gyroid heat-dissipating structures. AlSi10Mg with 5 vol.% diamond reached ~97% density, formed beneficial Al₄C₃ interfaces, increased Young’s modulus to 95 GPa (in-plane) and 85 GPa (build direction), and allowed complex lightweight heat sinks (hollow tubes, spirals, columnar arrays). The critical fs laser polishing step addressed LPBF roughness and diamond hardness: a 4° grazing-angle approach with optimized parameters (8 W, 220 kHz, 400 fs pulses, 5 μm hatch, 1 m/s) reduced surface roughness from 15.36 μm to 0.497 μm (97% improvement), producing submicron finishes and 500 nm periodic ripples on both Al and diamond phases without excessive oxidation or damage. This integrated process combines AM design freedom with precision post-processing to deliver high-performance diamond MMCs for electronics, aerospace, and beyond.

Prof. Yongfeng Lu is the Lott Distinguished University Professor in the Department of Electrical and Computer Engineering at the University of Nebraska-Lincoln, where he has served since joining in 2002 (with a courtesy appointment in Mechanical and Materials Engineering since 2018). A leading expert in laser-based micro/nanoscale material processing and characterization, he has authored or co-authored over 600 peer-reviewed journal articles and more than 500 conference papers, accumulating over 30,000 citations with an h-index of 85, placing him among the world's top 2% scientists. His groundbreaking work spans femtosecond laser nanofabrication, resonant vibrational excitation for rapid synthesis of diamond and GaN, laser peening to combat corrosion in naval alloys, two-photon polymerization for inertial confinement fusion targets, and advanced optical spectroscopy for energy, sensing, and extreme-environment applications. Securing over $40 million in funding from NSF, DoD, DOE, and industry partners, Prof. Lu holds 28 patents and has earned prestigious honors including the SPIE 3D Printing Award (2024), LIA Schawlow Award (2016), and UNL's Outstanding Research and Creative Activity Award (2017). As a Fellow of SPIE, LIA, OSA, and IAPLE, he has led major societies as President of LIA (2014) and IAPLE (2017–2019), serves as International Editor-in-Chief of the International Journal of Extreme Manufacturing, and has mentored dozens of PhD graduates and postdocs while driving innovations in clean energy, advanced manufacturing, photonics, and fusion research.

Sub-surface defects and residual stress are critical limiting factors to the damage threshold of high-power optics. To realize defect detection and locate the abnormal areas of optical components, a high-sensitivity detection method is developed based on the principle of digital holographic photoelasticity measurement. The phase difference associated with the two holograms before and after loading is calculated. Variables concerning birefringence are solved by obtaining multiple groups of holograms with different reference polarization directions and constructing a ratio function containing only the interference light intensity. Based on the time-averaged digital holographic technology, a vibration deformation measurement system and a full-process image processing solution for defect identification of optical materials are developed. The abnormal amplitude characteristics of the defects re verified by finite element numerical simulation. Through the double beam expansion setting and imaging adjustment, it is suitable for measuring optical materials with non-specular surfaces. The results show that the abnormal area in the phase difference image before and after vibration can effectively characterize surface and internal defects, proving that this method has a high detecting sensitivity.

Xiangchao Zhang is currently a full professor at Fudan University, China. He is a Senior Member of SPIE, and a committee member of ISO TC 213, SAC TC 240 and IMEKO TC 21. He serves as a trustee of Shanghai Optics Society, Precision Machinery Sub-society and IC Measurement and Instrumentation Sub-society of China Instrument and Control Society, and Vision Measurement Sub-society of China Society of Image and Graphics. He graduated from University of Science and Technology of China in 2005 and received his PhD degree at University of Huddersfield, UK in 2009. Prof Zhang’s research interests include precision optical measurement and computational imaging. He has published more than 200 papers. He won a second prize of Science and Technology Development of Ministry of Education of China, a golden award of the Geneva Invention Exhibition, and a second prize of Technical Progress of Chinese Society of Optical Engineering. He is an editor of Surface Topography: Metrology and Properties, Optics and Precision Engineering etc and a peer reviewer of more than 30 international journals and a project reviewer of NSFC of China and EPSRC of UK.

Recent growth of interest to the high-intensity laser-material interactions at femtosecond (fs) timescale is strongly motivated by development of high-power laser facilities for fusion. With typical pulse duration below 100 femtoseconds (fs), the photoionization is one of the major mechanisms to initiate laser-induced damage (LID) in optical components by the pulses. In this talk, we overview the state of the art in modeling laser-driven ionization of transparent materials. We start with the Keldysh photoionization rate for crystals and discuss several fixtures to it including rarely addressed oscillatory terms of the Keldysh formula and influence of symmetry of crystalline structure. We demonstrate how a proper choice of polarization direction aligned parallel to specific directions in crystals can suppress photoionization by order of magnitude. We also discuss options to suppress the ionization dynamics via combined choice of central laser wavelength, spectrum bandwidth, and peak intensity based on band structure of specific materials. We further discuss an interplay between the photoionization, free-carrier heating, and impact ionization based on several models including the Drude free-electron model, multiple-rate equations, particle-in-cell methods, and the Vinogradov equation. A major emphasis is put on validity and accuracy of the impact-ionization models. Future steps on developing ionization models are outlined with major emphasis on considering realistic band structure of the solids of interest, integration of the ionization simulations with modeling of other laser-induced processes in transparent solids, and modeling of ionization by few-cycle laser pulses with large spectral bandwidth.

Dr. Vitaly Gruzdev received his MS degree in Optical Engineering from Institute of Fine Mechanics and Optics (ITMO, St. Petersburg, Russia) in 1994, and Ph. D. in Optics from the Federal Research Center “S. I. Vavilov State Optical Institute” (St. Petersburg, Russia) in 2000. In 2005 he joined the Department of Mechanical & Aerospace Engineering, University of Missouri in Columbia, Missouri, USA. Since 2018 he has been a Research Associate Professor with the Department of Physics & Astronomy, the University of New Mexico in Albuquerque, New Mexico, USA. Theoretical description and simulations and theory of high-intensity ultrafast laser interactions with transparent solids, nonlinear absorption, laser-driven electron dynamics, and photoionization are his major areas of research. His achievements were recognized with a Newton Award for Transformative Ideas during the COVID-19 Pandemic in 2020 and ITMO Fellowship in 2025. He is a senior member of SPIE and Optica. He has co-chaired SPIE High Power Laser Ablation since 2024. Since 2009 through 2024 he was a co-chair of annual SPIE Laser Damage Symposium. He has been a guest editor of multiple special sections of Optical Engineering and JOSA B journals on laser damage, laser ablation, and high-power laser-material interactions since 2016.

Low-loss interference coatings are key components in advanced laser systems, particularly in applications requiring high laser-induced damage threshold (LIDT). The demanded substrate size spans a wide range, from a few millimeters to nearly 1 m, and the trend toward larger optics continues. Scaling deposition processes to such dimension’s places stringent demands on coating equipment, including uniformity over large apertures, suppression of coating defects, thermal management, and high process reproducibility. This contribution compares deposition equipment for large-substrate optical coatings using three physical vapor deposition technologies: ion beam sputtering, magnetron sputtering, and plasma-enhanced evaporation. These methods are assessed with respect to achievable absorption, interface quality, scatter, defect density, and their suitability for processing large and heavy substrates. Special emphasis is placed on equipment design features such as chamber architecture, source arrangement, substrate transport, thickness control, and process stability. The presentation focuses on oxide laser coatings, especially mixed HfO₂/SiO₂ and Ta₂O₅/SiO₂ layers deposited by ion beam sputtering on substrates up to 600 mm in diameter. Optical constants, deposition rates, and LIDT values are presented and discussed regarding the requirements of large-scale coating production.

Dr. Harro Hagedorn studied physics at the University of Hamburg and received his PhD in 1995 from the Institute of Applied Physics, University of Hamburg, for work on ion-assisted deposition processes. After R&D work on optical coatings for IR laser applications and optical coatings at Leybold Systems GmbH, he held several leadership positions within Leybold Optics, including Head of R&D in Hanau and later General Manager R&D Optical Coating Technology in Alzenau. Since 2012, he has been Head of R&D, Optics Division, at Bühler Leybold Optics.

High-power laser systems impose stringent requirements on the damage tolerance of ultraviolet optical components. In contrast to near-infrared laser-induced damage in optical coatings, which is dominated primarily by thermal effects, ultraviolet laser-Induced damage threshold (LIDT) is mainly governed by field effects coupled with thermal effects. The corresponding damage threshold is determined by multiple factors, including the intrinsic properties of the material, defect characteristics, and interface properties. In this study, high-reflectivity coatings for 355 nm UV regime laser applications were fabricated using ion beam sputtering (IBS) coating system. Large area IBS coating systems can achieve D800mm diameter area with uniformity better than +-0.5%. Two coating strategies were comparatively investigated: conventional high/low refractive-index (HL) multilayers and hybrid gradient refractive index (Rugate) designs using Hafnium dioxide (HfO2) films and Silicon dioxide (SiO2) films. The research focuses on elucidating the formation and growth of ultraviolet damage precursors under quasi-continuous interfacial systems and clarifying the suppression mechanism of quasi-continuous interfaces on such precursors. Furthermore, static and dynamic characterization methods were combined with time-resolved pump-probe shadowgraphy (TRPPS) to capture the ultrafast dynamic evolution of plasma expansion, shock-wave propagation, material ejection, and coating delamination during nanosecond laser-induced damage, thereby providing theoretical and technical support for the development of optical thin films with high ultraviolet laser-induced damage thresholds.

Michael Von Gruenhagen is a large coating area expert at Cutting Edge Coatings GmbH (CEC). He studied nanotechnology at the Gottfried Wilhelm Leibniz University Hannover and earned a Master of Science degree. He has been involved in research on IBS coating technology at CEC since he did his master studies. With his effort, CEC has successfully developed and manufactured large-area IBS coating equipment, which can reach D800mm diameter uniformity better than +-0.5%. In last year, he was also invited to give a talk at the 8th Annual Optical Young Scientists Conference in Qingdao. Now he continues to do further research on the laser-Induced damage threshold LIDT of IBS films at ultraviolet regime. Michael Von Gruenhagen is also CEC's director for the Asian market and is highly regarded by clients.

A study on laser amplifier of kJ level energy output laser has been proposed,which include the key units development and the art of state of configuration of the laser system. A flashlamp-pumped Nd:glass mutli-frequency laser amplifier has been developed,which has a 150mm*150mm aperture laser output and the small signal gain efficent 4.88%/cm.One single set amplifier can produce 1.18 times gain and the stored energy was 230J.This amplifier can run under 1Hz which has a better performance than the same type amplifier of CEA of Franch and son on.A new configuration of laser system which include all image transfer,coaxial, thermal depolarization self-compensation and circle multi-pass technology has been proposed which can been used on kJ classic,ns pulse muliti-frequency laser system.The experement result indicates that this configuration can suppress the reverse laser and self-excitation laser. A 80mm aperture laser output with 155J/10ns had been achieved,and the extrapolate output with the whole aperture maybe be better than 500J,which can play a important role on kJ classic laser output laser development.

Lin Chen is an associate professor at the Laser Fusion Research Center, China Academy of Engineering Physics. His research focuses on high‑power solid‑state laser technology. He proposed the "high‑voltage short‑pulse" technique for a 400‑mm‑aperture, 4×2 slab amplifier system in an ICF high‑power laser, enabling it to achieve internationally leading performance. His work also includes the development of nanosecond, high‑repetition‑rate laser technologies, with demonstrated outputs of 400 J/1 Hz and 10 J/100 Hz. He has received two provincial/ministerial‑level awards, published over 30 papers, and holds more than 10 authorized invention patents.

Understanding defects in optical materials is crucial for their use in advanced optical components. As fused silica (SiO₂) is one of the most widely utilized materials, gaining detailed insight into its defect structure is particularly important. This presentation outlines our recent work on understanding the defects involved in SiO₂ using photoluminescence (PL) and laser-induced fluorescence, combined with analysis based on the Franck–Condon (FC) model. Defects in SiO₂ are commonly identified through PL emission spectra, often interpreted using multiple Gaussian components. In this study, we extend this conventional approach by applying the FC framework to gain deeper insight into defect states and the associated charge carrier relaxation mechanisms. In addition, certain defects are generated only under laser irradiation. To explore this, we examine the formation of laser-induced defects in SiO₂ under prolonged UV exposure (257 nm). By employing a multi-transition FC model, we further clarify the role of precursor states involved in their formation. Overall, combining PL measurements with FC analysis provides a more detailed understanding of defect formation and evolution in fused silica.

Mariem Guesmi is a researcher at the Research Centre for Special Optics and Optoelectronic Systems, part of the Institute of Plasma Physics of the Czech Academy of Sciences, where she has been active since 2019. She earned her PhD in 2017 in Tunisia, with research centred on organic polymers, focusing on their structural and optical properties for next-generation optoelectronic applications. Following her doctoral studies, she joined the Institute of Macromolecular Chemistry of the Czech Academy of Sciences as a postdoctoral researcher in 2018, where she worked on hybrid and organic materials, including perovskites, investigating their morphology–property relationships and their potential in advanced optoelectronic devices. Since 2019, her research has expanded toward ultrafast optics and laser–matter interaction, with an emphasis on photoluminescence spectroscopy, and the study of defect-related emission in optical materials. Her work integrates experimental spectroscopy to better understand light–matter interactions, contributing to the development of high-performance optical materials.

High-laser-damage-threshold (LIDT) optics operating in the 0.8–2 m wavelength range, with pulse widths from femtoseconds to nanoseconds, have been under development for several years. Manufacturing meter-scale optics that simultaneously achieve high LIDT and superior surface quality remains a significant challenge. Currently, meter-scale substrates coated with ion-assisted electron-beam evaporation on fused silica or low-thermal-expansion glass ceramics have demonstrated excellent performance in high-power laser systems. In this paper, we present our manufacturing capabilities for meter-class optics used in 10-PW-class lasers. Furthermore, we report recent LIDT result at the 2 m wavelength.

Takuya Mikami joined Okamoto Optics Works, Inc. (currently Okamoto Optics, Inc.) in 2002, where he has been engaged in the development of high-power, large-aperture optical components for advanced laser applications. He received his Ph.D. in Science and Engineering from the Graduate School of Photonics Science, Chitose Institute of Science and Technology, in 2011. In 2020, he was appointed as a Visiting Professor at the Institute of Laser Engineering, Osaka University. Since 2024, he has served as Director and Head of the Technology Division at Okamoto Optics, Inc.

The quintic nonlinearity coefficient n4 (nonlinear susceptibility χ(5)) of fused silica was measured using a modified z-scan technique, extended for a cubic-quintic nonlinearity model, at femtosecond pulse intensities on the order of 10TW/cm2. The obtained values of n4 = −5.5(±1.2)·10−6 cm4/TW2 at a wavelength of 1033 nm and n4 = −12(±4)·10−6 cm4/TW2 at 517 nm are significantly lower than the previously reported data.

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Water, or heavy-water face-cooling of multi-disk amplifier is considered as a potential route to reach the 10 kilowatt landmark of average power for intense short-pulse lasers, paving the way to crucial laser-based societal applications. With this cooling technique, amplifiers disks are operated underwater, requiring to study their underwater damage behaviour. We report a study of laser induced damage thresholds of hafnium oxide anti-reflection layers deposited by Ion Beam Sputtering on Ytterbium:YAG crystals, at a wavelength of 1 μm, and compare the damage thresholds in air and underwater. The measured damage thresholds are either equal or higher underwater than in air. We present a one-dimensional electromagnetic model that assumes water permeation into the coating, resulting in stronger field enhancements in air than underwater next to sub-surface damage precursors, thus suggesting a possible explanation. Importantly, the lower underwater damage fluence measured for 1 ns pulses is equal to the saturation fluence of Yb:YAG at room temperature. We eventually show how a single amplifier head based on rotating-multi-disk Yb:YAG operated under heavy water may reach an average power of 2 kW in continuous wave operation.

Dr Philippe Balcou is Directeur de Recherches de Classe Exceptionnelle at CNRS, France. He graduated from Ecole Polytechnique in 1989, received a PhD in optical and quantum physics from Université Pierre et Marie Curie in 1993, under supervision from Pr A. L'Huillier. He was director of Laboratoire d’Optique Appliquée in 2003-2004, director of the Centre Lasers Intenses et Applications from 2007 to 2016, member of the Scientific Council of CNRS from 2018 to 2023. He serves currently as secretary to the International Union of Pure and Applied Physics C17 committee on laser physics. As a former co-worker of two Nobel laureates, he received the Aimé Cotton prize of the French Physical Society for his contributions to the physics of high harmonic generation and attosecond science.

With the drive to achieve higher laser powers for applications such as inertial confinement fusion the requirements of the optical components with respect to resistance to laser induced damage (LIDT) are increasing. Within optical thin films both intrinsic defects, such as structural imperfections or vacancies, and extrinsic defects, like particle contamination often lead to an earlier onset of damage. Intrinsic defects may change the electronic structure of the materials, and in particular introduce intermediate states between the valence and conduction bands. These are considered to be a critical aspect, when it comes to femtosecond laser induced damage as the primary mechanism for damage, is the ionization through nonlinear absorption processes. We present a brief summary of previous works, along with details to our expansion of existing theoretical models and compare these to experimental results. The influence of defect properties on the behavior of the nonlinear absorption is also discussed. Extrinsic defects, such as nodules or contamination through particles, are typically considered less problematic for ultra short pulse durations where thermal effects dominate. However, these defects may lead to electric field enhancements within the coating, which due to nonlinear absorption processes, will reduce the LIDT even under femtosecond irradiation. We show through measurements that the inclusion of transparent particles within the coating leads to an associated reduction in ultra-short pulse LIDT, and discuss mitigation strategies. In the presentation, the influence of the coating procedure and the coating parameters, on both, the geometrical, as well as the electronic structure is discussed.

Joshua McCauley is a researcher at the Laser Zentrum Hannover e.V. in Germany, specializing in ultra short pulse interactions with optical coatings, with a focus on nonlinear absorption. He obtained his bachelor in Mathematics and Physics from Victoria University of Wellington in New Zealand. He then completed his masters in physics at the Karlsruhe Institute of Technology in Germany.

Deep-ultraviolet (DUV) coherent light sources, with wavelengths shorter than 200 nm, have important application value in fields such as microcircuit lithography, high-density storage, high-resolution imaging, and laser micromachining, owing to their unique characteristics of short wavelength, high photon energy, and excellent beam quality. As the key functional material system for all-solid-state DUV laser systems, DUV optoelectronic functional crystals play crucial roles. Specifically, DUV nonlinear optical crystals mainly undertake the core function of frequency conversion, while DUV birefringent crystals are primarily responsible for key functions such as polarization modulation and beam separation. Our research group proposes that the fluorooxoborate system including anionic groups [BO4-xFx] (x = 1, 2, 3) is a preferred system for the design and preparation of DUV nonlinear optical crystals. Through exploration in this system, a series of fluorooxoborate-based DUV nonlinear optical crystals, represented by ABF, have been discovered, enabling direct second-harmonic generation (SHG) output of DUV laser with the shortest wavelength reaching 158.9 nm. Based on the strategy of designing DUV birefringent crystals using [BO2] groups and [BO2]∞ chains, we have developed DUV birefringent crystals such as CB2 and LB, and successfully fabricated the first DUV Glan polarizer. The applicable wavelength band has been extended to the DUV region by approximately 20 nm compared with the commercial α-BBO birefringent crystal.

Fangfang Zhang, a researcher at the Xinjiang Technical Institute of Physics and Chemistry, Chinese Academy of Sciences, mainly engages in the research on new optoelectronic functional crystal materials. As a key contributor, she invented the ABF family of fluorooxoborate deep-ultraviolet nonlinear optical crystals and the CB2 series of deep-ultraviolet birefringent crystals. She has published more than 100 papers in journals such as Nature, Natl. Sci. Rev., J. Am. Chem. Soc., and Angew. Chem. Int. Ed., et al, and has been granted more than 20 Chinese and international invention patents. She presides over projects including the Type B Pilot Special Project of the Chinese Academy of Sciences, the National Key Research and Development Program, and the National Natural Science Foundation of China for Young Scientists (Type B).

Surface micro-defects on large-aperture high-power laser optics readily induce laser damage, severely limiting component lifetime and the stable operation of inertial confinement fusion facilities. To address defects of different scales and types, this study develops rapid detection and precision repair technologies. A detection method integrating a convolutional neural network and a three-light-source optical field coupling system enables efficient localization over a 430 mm × 430 mm aperture (detection time ≤5 min, positioning accuracy ≤5 μm, recognition success rate ≥98%). For KDP crystals, plastic-domain micro-milling repair is adopted, and a machine vision‑based intelligent tool alignment technique achieves alignment accuracy better than 1.5 μm and single alignment time <1 min. The repaired surface roughness Ra is <30 nm, and the laser‑induced damage threshold exceeds 90% of the substrate. For fused silica, a size‑dependent hierarchical repair strategy is proposed: for sub‑5 μm full‑surface distributed defects, CO₂ laser polishing heals the surface via large‑area scanning melting; for 5–50 μm small defects, femtosecond laser ablation provides high‑precision material removal; for defects >50 μm, CO₂ laser evaporative ablation achieves a single‑point repair time as short as 17 s, Ra <15 nm, and a damage threshold reaching 95% of the substrate. These technologies have been applied in inertial confinement fusion facilities, repairing nearly 1,000 large‑aperture components and saving over 74 million CNY, effectively suppressing defect‑induced damage growth. An automated inspection and repair production line is being established to achieve an annual capacity of 2,000 pieces, providing key technical support for long‑term operation of high‑power laser facilities and fusion energy engineering.

Linjie Zhao, Professor at Harbin Institute of Technology (HIT), specializing in ultra-precision manufacturing and service performance evaluation of high-power optical components, optical surface defect detection, and robotic assembly. He has been selected for the 10th "Young Elite Scientists Sponsorship Program" of the China Association for Science and Technology and the "Qihang Scholar (Full Professor)" Talent Recruitment Program of HIT. He has received the First Prize of Technological Invention Award of the Ministry of Education, the Outstanding Award of China Patent Award, and the Silver Award of Heilongjiang Province Patent Award. He has led more than 20 research projects, including projects from the National Key Research and Development Program, sub-projects of the Major Program of the National Natural Science Foundation of China (NSFC), the NSFC Youth Fund, and the China Postdoctoral Special Funding. He has published over 100 SCI-indexed papers and filed more than 80 invention patents, of which over 40 have been granted.

Large-aperture, low-loss laser optics constitute a critical performance bottleneck in high-power laser systems, where comprehensive metrics—including transmission efficiency, surface figure accuracy, and loss levels—dictate overall system performance and reliability. This research achieved breakthroughs in ultra-smooth substrate processing by synthesizing a Ce³⁺-enriched ceria polishing slurry (primary particle size <2.5 nm, agglomeration strength <20 MPa), enabling fabrication of 400mm-aperture substrates with sub-50pm surface roughness and minimal defects. For optical coatings, a stress-strain control methodology was established through thin-film mechanics analysis, achieving sub-millimeter curvature accuracy for large-radius spherical optics (>1m) and high-precision surface figure control for planar components. Furthermore, crystallization suppression in HfO₂ films combined with step annealing significantly reduced optical losses. Utilizing EB-IAD technology, we fabricated large-aperture high-power reflective coatings compatible with both continuous and pulsed lasers, demonstrating >99.999% reflectivity at 1064 nm, continuous-wave damage threshold >5 MW/cm², and pulsed-laser damage threshold >40 J/cm² (6ns, 1Hz). These technologies currently support annual production of over 4,000 components for operational high-energy laser facilities.

Deng Songwen, Researcher at the Dalian Institute of Chemical Physics, Chinese Academy of Sciences, specializes in manufacturing and performance evaluation technologies of high-power laser thin-film components. He has been awarded Second Prize of the for Scientific and Technological Progress (Provincial Level) and the First Prize for Technical Invention of Dalian. He has led or participated in over 20 research projects funded by national and institutional programs, including the National Key R&D Program, National Natural Science Foundation Youth Fund, and CAS Key Laboratory Funds. His scholarly output includes 20+ publications, and he has contributed to the formulation of 6 National Standards.

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The Dynamic chemical etching (DCE) serves as a mainstream key technique to control damage precursors on fused silica surfaces and enhance the ultraviolet (UV) pulsed laser-induced damage performance. Nevertheless, constrained by the redeposition behavior and isotropic mechanism of wet etching, the upper limit of damage performance improvement for fused silica is restricted, and the surface roughness of optical components is degraded. To tackle this problem, an ultra-smooth control strategy for damage precursors on fused silica surfaces is proposed, which combines dry physical etching and wet chemical etching. In this composite method, the subsurface damage layer and surface polishing redeposition layer are first removed tracelessly by flexible ion beam etching. Subsequently, ultra-purification of absorptive impurities on the fused silica surface is achieved via oxidative leaching and mega-sonic assisted wet etching. Experimental results demonstrate that the surface roughness of fused silica after composite treatment can be further reduced to approximately 0.2 nm. Compared with the standard DCE process, the UV pulsed laser-induced damage density is decreased by 1–2 orders of magnitude, realizing the synergy of high laser damage resistance and ultra-smooth surface. Further physical mechanism analysis reveals that the ultra-smooth surface obtained by dry physical etching can significantly reduce the viscous boundary layer (VBL) on fused silica surfaces during wet chemical etching. It prominently promotes the mass transport of etching products in the etching and pull-dehydration processes, thus further alleviating the redeposition issue in wet etching.

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Ultraviolet laser damage of final optics is the key issue of high power laser driver for ICF. Laser damage is the result of high power laser interaction with optical material, and laser intensity and energy density are the main parameters. In this talk, we will present the precise manipulation of laser damage of optical materials by managing the defect excitation and energy deposition with pulse temporal shaping. Both damage threshold and morphology are significantly modulated by pulse-train shaping. The ramp-up-shaped train effectively increases its damage threshold and decreases the damage density and size. The temporal evolution of damage modulation is experimentally revealed by varying the interval of pump-probe pulses. The underlying mechanism of the temporal-shaping effect on laser damage is discussed based on the applied precursor modification to absorption enhancement, which could provide insights for studying ultraviolet laser damage of fused silica optics.

Mingying Sun is a researcher in National Laboratory on High Power Laser and Physics, SIOM, CAS. He received his Ph.D. degree in Optical Engineering from SIOM in 2014. His is currently focused on the target area of high power UV laser facility and applications for inertial confinement fusion. His research interests include laser damage, laser micromachining, frequency conversion and parametric amplification, laser propagation, laser illumination on ICF target and so on.

This study elucidates a critical, previously underestimated damage mechanism responsible for the failure of optical components operating substantially below their nominal laser-induced damage threshold (LIDT) in Nd:glass regenerative amplifiers. We identify a self-reinforcing, defect-assisted thermal dissociation feedback cycle. Within the burst environment of a regenerative amplifier, where the inter-pulse interval is shorter than the material's thermal relaxation time, significant heat accumulation occurs at localized absorbing defects, forming microscopic hotspots. When the temperature of these hotspots exceeds the thermal dissociation threshold (typically 260–600 °C for fluoropolymer) of adsorbed molecular contaminants, thermal decomposition is triggered. The subsequent deposition of strongly absorbing pyrolytic carbonaceous products dramatically enhances local energy absorption, thereby accelerating thermal accumulation, eventually drives the local temperature beyond the critical thermal damage temperature of the coating material, culminating in irreversible damage. These findings reveal a distinct, thermally dominated damage pathway that predominates under infrared laser irradiation at intensities on the order of MW/cm² or lower, contrasting with previously described photochemically governed mechanisms common at shorter wavelengths or higher intensities. This work highlights a significant long-term reliability concern for regenerative amplifiers and provides crucial guidance for the design, stringent contamination control, and maintenance of infrared laser systems.

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