This PDF file contains the front matter associated with SPIE Proceedings Volume 11514, including the Title Page, Copyright information, and Table of Contents.

The past several decades have witnessed major advances in high-power lasers. The 2018 Nobel Prize in Physics awarded for Chirped-Pulse Amplification recognized the revolution underway in high-power lasers. The development in both peak- and average-power lasers has been motivated by the many applications in science, national security, and industry that such lasers enable. In this presentation, applications including laser accelerators, fusion and high-energy-density research,and directed-energy weapons that motivate their development and the status and a vision of the future of high-power lasers will be discussed. This material is based upon work supported by the Department of Energy National Nuclear Security Administration under Award Number DENA0003856, the University of Rochester, and the New York State Energy Research and Development Authority. The support of DOE does not constitute an endorsement by DOE of the views expressed in this abstract.

Ultra-high peak power femtosecond ultrafast lasers with peak powers at the level of 10 petawatt or even higher have led to the generation of unprecedented extreme physical conditions in laboratories, which pave new ways to the long standing pursuit of fundamential science and the promising applications. The Shanghai Super-intense Ultrafast Laser Facility (SLUF) with 2 laser beamlines of 10PW and 1PW peak powers will be available to users this year. The 100 PW laser system as the core machine of the Station of Extreme Light (SEL) which is one of the stations at Shanghai High repetition rate XFEL and Extreme light facility (SHINE), is being developed and scheduled to be ready in the next 5 years. I will described the progress and challenges of SEL and SHINE.

The National Ignition Facility in northern California routinely operates at twice the intensity (fluence) known to damage fused silica optics. With this in mind, the facility was designed and built with removable optic modules that allow for optic exchanges which in turn enable an optics "recycle loop" to extend the life of highly specialized optics. The recycle loop includes automated optics inspection whereby every damage site is identified, measured, tracked through time, protected (once it approaches an optic-specific size limit), and then repaired in a laboratory so the optic can be reused. Here we describe an overview of custom image analysis, machine learning, and deep learning methods used throughout the recycle loop for optics inspection on the NIF beamlines and off. Since 2007 we’ve used machine learning to improve accuracy and automate tedious processes to enable and inform an efficient optics recycle loop. This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344. LLNL-CONF-749953

This paper gives the annual report on the progress of developing a US National Standard. Effort in this past year has been on derivation of test details [1] and an initial test plan to validate the test. This initial test is a major lesson learned in the development of the ISO standard tests, namely it will allow for the experimental validation of key assumptions in the test procedure. Among these key assumptions to be validated are that the exposure sequence is properly described by a Poisson sequence and the role of spot size on counting rate accuracy. Our results and the impact of these results on the test procedure will be given. The next steps in the development of the standard will be discussed.

Quality standards are the basis for establishing a common ground between both research institutions and commercial organizations that exchange quantitative information about product features and related issues. In the rapidly changing world, the field of photonics is at the forefront of innovation: research, development, and manufacturing of new types of optics and lasers take place daily. In this context, new important aspects and limitations of the current damage testing approach become apparent. Accordingly, the ISO family of standards (ISO 21254) related to laser-induced damage threshold testing is reviewed and updated regularly. Various inputs into laser-induced damage testing were collected over the years by Lithuanian laser-induced damage community, which is a long-time practitioner of the current and previous revisions of ISO standards. Within this presentation, an attempt is made to contribute to the tremendous work that has already been done. Two types of efforts are made. First of all, we seek to identify weak points, edge cases and areas that leave some space for various misinterpretations and systematic errors. Secondly, we propose possible solutions (with corresponding Monte Carlo simulations for validation) that are currently in practice at laboratories of Lidaris UAB and Laser Research Center of Vilnius University. The suggested inputs are mostly related to definitions of damage criteria, test procedures, analysis of results, selection of appropriate testing protocols and their parameters as well as data representation. By no means, our observations seek to diminish the value of present approaches. As imperfect as they are, current standards were the only appropriate reference for a long time and proved to be adequate in most cases. We believe that the idea of a single protocol that would address all the issues of the community is flawed (considering the wide gamut of optics and lasers), therefore different testing protocols should be viewed as tools to address different problems. We also hope that some of our quantitative inputs could bring more clarity to preconceptions about laser-induced damage testing and significantly improve current approaches.

The paper aims to compare the results obtained with the same laser source with a large beam and with small beams. These latest were shaped from phase objects implemented to obtain several small beams from a single larger beam. The consistency of the results from both sets of measurements is shown. It validates the assumptions made and the specific mathematical treatments implemented to establish the link between the two approaches. It also validates and strengthens the approach developed from the rasterscan procedure used to measure damage densities from the scanning with beams of small dimensions. This shows that small beam tests are reasonably representative of tests carried out with large beams.

It is crucial in the laser optics industry to have reliable Laser Induced Damage Threshold(LIDT) testing to ensure quality optics that laser users can rely on, especially for high power or fluence laser experiments. In-house testing not only provides the QA/QC utility but also the necessary feedback loop to improve and develop quality laser optics. We present the development of a robust LIDT testbed at Edmund Optics with enough adjustability to accommodate testing according to the ISO Standards 21254 -1,-2,-3 and -4, in addition to applying new parameters and protocols for LIDT testing such as those being developed by the Optics and Electro-Optics Standards Council Task Force 7 (OEOSC-TF7). Difficulties in developing such a complex system(safety, automation, damage detection, etc.) will be presented as well as test results produced by the system to-date.

The Laser MegaJoule (LMJ) is a 176-beamlines facility, located at the CEA CESTA near Bordeaux (France). It is designed to deliver about 1.4 MJ of ultraviolet laser energy on targets set in vacuum chamber, for high energy density physics experiments, including fusion experiments. The commissioning of the seven first bundles of height beams is achieved since November 2019 and the commissioning of next bundles is on the way. For performance requirements, it is important to follow final optics behavior. Moreover, for questions of manufacturability, ease of maintenance and cost, the understanding and the improvement of vacuum windows laser damage resistance are of main importance. The MDCC (Center Chamber Diagnostic System) is thus operating since November 2018 on the LMJ facility. It consists in a high resolution CCD camera combined with a predefined focus set of optics. The resolution of this system is about 100μm with a working distance of 8 m. This system can perform 3 functions: damage detection on the vacuum window surface, the measurement of the spatial profile on the vacuum window plane and of final optics transmission.

Ultrafast lasers enable non-contact, waste free, precise material removal. We have demonstrated single-digit nanometer precision polishing of optical material using a femtosecond laser. For ultrafast-laser-based waveguide writing, we study the underlying physics behind nonlinear optical dynamics during the femtosecond laser processing of crystalline materials. Unidirectional pulse propagation equation simulation is carried out to study the evolution of energy, fluence, plasma generation, and beam waist of a femtosecond pulse along the propagation direction under different energy and focusing conditions. Waveguides having a loss of 0.21 dB/cm are obtained. A Nd:YAG based waveguide laser with lasing threshold of 50 mw was demonstrated.

Understanding interactions of ultrashort laser pulses with ceramics and glasses is critical for advancing the frontier of ultrafast materials science and producing novel states and structures in glasses, ceramics, and glass-ceramics. First, an overview of generation and control of ultrashort pulses covering nano-, pico-, femto-, and attosecond timescales will be presented. Chirped pulse amplification (CPA) that led to advancement of ultrashort laser pulses will be introduced, followed by details on how these pulses interact with materials. Linear and nonlinear optical processes induced by the laser pulses will be discussed. Feasibility of high-harmonic generation (HHG) in quartz crystal, fused silica, and oxides reported in the literature will be presented. Femtosecond laser based processing e.g., writing of wave guides, gratings, band gap structures, ceramic microstructuring, and glass strengthening, will be described. The presentation will conclude with the promise of extreme light sources in study of materials, particularly ceramics and glasses.

Epsilon-near-zero-materials and their unique properties are key to successful integration and miniaturization of optical components. Novel concepts, which promise significant progress in this field of research, such as optical switches and thin film electro-optical modulators, are possible, when the electrical and optical properties of ENZ-materials are carefully exploited. To achieve a greater understanding of these properties, this contribution investigates the electrical conductivity, optical transmittance as well as losses of thin indium tin oxide films and links them to their LIDT at various ultrashort pulse durations.

This year’s competition aimed to survey state-of-the-art visible high reflectors in the nanosecond pulse length regime. The requirements for the coatings were a minimum reflection of 99.5% at 0 degrees incidence angle light at 532-nm. The choice of coating materials, design, and deposition method were left to the participants. Laser damage testing was performed at a single testing facility using the raster scanning test protocol with a 6-ns pulse length laser system operating at 100 Hz in a single-longitudinal mode. A double blind test assured sample and submitter anonymity. The damage performance results (LIDT), sample rankings, details of the deposition processes, coating materials and substrate cleaning methods are shared. We found that hafnia/silica multilayer coatings deposited by all five deposition methods surveyed were the most damage resistant within their group under these test conditions. In addition, hafnia/alumina/silica designs deposited performed second best.

We present an approach for wafer-level rapid multi-modal defect non-destructive imaging of device-relevant GaN defects with high resolution and high sensitivity. The scanning GaN defects detection system is based on laser pump-and-probe photoluminescence and photothermal measurements that are compared to diode device reliability data from accelerated lifetime testing. This work hypothesis is that defects probed at optical frequencies can reliably predict reliability or performance issues of power electronic devices at near DC frequencies. Imaging, growth, and device data are correlated to validate the proposed multi-modal defect detection approach for detection of GaN defects relevant to power electronic devices.

If Jena, Germany has a sister city of light in North America, it is certainly Rochester, on the "north coast" of the United States in New York’s beautiful Finger Lakes region. Home to more than 120 OPI companies employing over 18,000 workers, New York Photonics members serve biomedical, aerospace, consumer products, research, automotive and defense-related markets with optics, photonics and imaging components and products. The history is old by North American standards, dating back to 1853 when Bausch and Lomb was established, and today includes important breakthroughs in free-form optics and integrated photonics. A broad historical perspective about America’s biggest and longest standing OPI cluster will be offered.

Ultrashort laser pulse interaction with solid contains an abundant electronic dynamic process. When the laser pulse width reached few-cycle area, surface damage behaviors can reflect the initial light-electron interaction. In this work, we employed an ultrashort laser source to investigate damage behavior on solid. We investigate the potential of the multi-plate medium to generate broad supercontinuum and few-cycle pulses from a relatively high peak and average power Yb solid-state laser source in a single-pass double-stage multi-plate supercontinuum setup. The experiments were performed by focusing the output from a Yb3+: KGW regenerative amplifier, producing pulses from energy of 600mJ(1kHz) and a duration of 170 fs(~5ps tunable), through a set of thin fused silica plates with individual thicknesses of 1mm to 2mm. This resulted in pulse width of 15fs-25fs (4 cycles-7 cycles) continuous tunable laser source to investigate the laser-induced damage behavior of ZnSe and Fused silica. The damage mechanism and damage threshold are explained in the context of the Keldysh theory and critical electron density.

Low energy of the photons of intense mid-infrared lasers favors generation of highly non-equilibrium free-carrier (FC) plasmas with high ponedromotive energy of conduction-band electrons. The plasmas are characterized by enlarged electron-phonon collision time, low free-carrier absorption, and extended lifetime of plasma’s non-equilibrium states in contrary to near-infrared and visible wavelengths. We propose a model that incorporates an energy-resolved rate equation for the laser-generated conduction-band electron density, the Keldysh photoionization, the Vinogradov free-carrier absorption, and the low-collision-rate model of transient optical response. We discuss proper criteria to evaluate threshold of laser-induced damage by applying the model to typical semiconductors.

This presentation will overview the evolution of optical manufacturing and coating technology from pulsed high energy laser optics to high power continuous wave optics. The journey includes lessons learned through rich collaborations between universities, national labs and companies that results in a holistic approach to advance the field of high-laser-damage optics.

Electric field enhancement of nodular defects in multilayer mirrors has been extensively modeled and experimentally validated. However, the impact of reflectance has not been sufficiently explored. Hafnia and silica are the most favored coating materials for high fluence optical and near infrared mirrors. In this study, hafnia and silica mirrors with a reflectance of 0.99, 0.999, 0.9999, and 0.99999 are generated by increasing the layer count >2×. Each of these cases is explored for light intensification at 0° and 45° incidence at both polarizations. The spatial and temporal characteristics of light intensification is examined for these different test cases.

Meter-scale transmission mirror was one of the most important components for the giant solid-state laser device. Innovative method was adopted to realized multi-performance control by coupling different steps. Meter-scale transmission mirrors with high comprehensive performance were firstly coated. And the results were the best as reported so far.

Third harmonic separator has proven to be a critical component in high-power laser systems, which can be used for beam splitting and optical path change of 355 nm laser. It is desirable for the coating to have high spectral efficiency and laser induced damage threshold. Through precise fabrication, the spectrum efficiency can easily meet the requirements with high reflection at 355nm and high transmittance at 532nm and 1064nm. However, the issue is more complicated and quite challenging for obtaining high LIDT, because high refractive index materials tend to have high absorption at ultraviolet, which contribute to a decreased LIDT together with the electric field inside the film. It is significant to investigate the interplay between absorption, electric field intensity and LIDT. In this paper, materials of HfO2 and SiO2 are used to design and fabricate the two third harmonic separator with similar film structure, high spectral efficiency and different electric field distribution by electron beam evaporation. Spectral measurements results show that the prepared samples all have similar spectra with high spectral efficiency. Damage threshold and weak absorption test results show that high intra-film electric field distribution results in higher weak absorption and lower damage threshold. Our research has important reference significance for the design and preparation of high damage threshold third harmonic separator.

Spaceborne LIDAR systems with high power laser optics enable advanced understanding of the climate change. However, nano-scaled particles originating from film deposition processes reduce the laser-induced damage threshold. A secondary ion source is used to remove the particles that settle on the surface of the growing film. A second option is to remove precursors by laser irradiation before they are covered with additional layers. To verify the impact on the defect mitigation, laser-induced damage threshold tests and raster scan tests were conducted. This work has been carried under the ESA contract AO 1-8683/16/NL/BJ activity with name “Particle mitigation in high power laser optics”.

We compare the 355 nm, 45º AOI p-pol 8 n-s laser damage performance of standing-wave hafnia single layers fabricated under the same conditions and annealed under different temperatures. An intriguing trend is observed in the laser damage performance with respect to annealing temperature, with a notable performance increase observed in the sample annealed at 250º C. Chemical compositional analysis via Rutherford Backscatter spectroscopy (RBS) indicates that annealing induces sub-stoichiometric hafnia films for high temperature annealing.

This presentation, originally published on 11 September 2020, was withdrawn per author request.

Plasma ion assisted deposition (PIAD) is a common method for the production of high-end optical interference coatings (OIC). Conventional process control is based on operating parameters like gas fluxes, voltages or currents, while the actual state of the assist plasma is specified imprecisely. The concept of active plasma resonance spectroscopy (APRS) employing the Multipole Resonance Probe (MRP) allows to access plasma conditions in industrial coating environments. This study presents results on the investigation of conventional and APRS-based control concepts for a multilayer OIC, a 36-layer polarizer made of SiO2 and Ta2O5. Process repeatability and its impact on Laser Induced Damage Threshold (LIDT) are addressed.

Plasma ion assisted deposition (PIAD) was employed to prepare a dense capping layer (seal the top surface only) or shell layer (seal both the top surface and the sidewall) of an e-beam coating. The lateral water vapor diffusion was confirmed by a monolayer e-beam coating with a capping layer. The stress evolution and spectral shift of the multilayer e-beam coatings with/without capping/shell layers were comparatively studied. The protective effect of the shell layer on the e-beam coating was further investigated by water bath treatment. The experimental results proved that the PIAD shell layer can be used to address the time-dependent and environmental reliability issues of the e-beam coatings for high-power laser applications.

It is well known that dielectric coatings used in high energy laser systems for beam steering are susceptible to laser damage. The laser damage ensued in high refractive index materials, such as hafnia, is responsible for limiting the laser operation fluence and lifetime. Although hafnia is an ideal high refractive index material used in dielectric coatings for a broad range of laser wavelengths, defects developed during the deposition process leads to laser-induced damage. In order to increase the resistance to laser damage and improve laser performance, it is imperative to understand the underlying physics of laser damage in high index coating materials. Earlier work observed a substantial difference in laser damage thresholds for hafnia coatings produced by different deposition methods, yet the underlying mechanisms for the observed difference remains elusive. In this work we investigated the responses of single layer hafnia films produced by two deposition processes, electron beam (e-beam) evaporation and ion beam sputtering (IBS) methods upon UV ns-laser exposure. The films underwent laser damage testing using a 1-on-1 laser damage testing protocol with a beam size of 650 µm (1/e2) at 355 nm and 8 ns pulse duration. Both S and P polarizations were tested at a 45° angle of incidence. Chemical, structural and morphological characterizations of the films both pre- and post-laser damage were performed using Rutherford backscattering spectroscopy, glancing incidence X-Ray diffraction, and optical and scanning/transmission electron microscopy. We found that films deposited from the e-beam process had a higher damage onset threshold (4.4 +/- 0.1 J/cm2) than those deposited by IBS method (2.1 +/- 0.2 J/cm2). Furthermore, a polarization-dependent damage threshold onset was observed for the e-beam evaporated coatings but was not observed in IBS films. Although the typical size of the damage in general is larger for the e-beam produced films, the morphology shows similar foamy appearance in both films. The density of the damage sites, on the other hand, was much greater in the IBS produced films than that by the e-beam method. The observed difference can be attributed to their resulting structural/textural differences inherited in each method: porous in the e-beam films and dense with isolated nanobubbles in the IBS films, which can lead to a large difference in laser-defect coupling. The underlying physical mechanism will be discussed in detail. This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344. IM Release# LLNL-ABS-809117

We present a method for producing spatially patterned glass engraved meta-surfaces, which is scalable, has high mechanical stability and high laser damage durability, and thus promising for ultra-thin optics implementation for high-power lasers. The process is based on laser raster-scan of a thin metal film on a glass, followed by dry-etching and removal of the metal mask. We present fabricated structures, characterization of their optical performance, mechanical stability and laser damage performance.

GaSe crystals that are promising as nonlinear optical converters in the mid- and far-infrared ranges are charac- terized by high Fresnel losses leading to transmittance per surface at the level of 77%. In this study, antireflection microstructures (ARMs) were fabricated on the surface of the GaSe single crystal by single-pulse femtosecond laser ablation. This method makes it possible to increase the transmission up to up to 92%.

This presentation, originally published on 11 September 2020, was withdrawn per author request.

We have previously shown that most of the laser-induced damage which occurs at the National Ignition Facility’s (NIF) Grading Debris Shields (GDS) is due to energetic, micron-scale particles generated by the laser interacting with other parts of the beamline. In this work we will review the mitigation strategies devised with an emphasis on the implementation and testing of a Fused Silica Debris Shield (FSDS). The preliminary results from the initial online test suggest that we are approaching intrinsic (debris free) damage levels where fluence distributions once again dominate initiation rates. We will explore the challenge of future projections of damage initiation and optics lifetime where we will need to model the maximum fluence at each location on an optic (i.e. Max-of-N) and how it increases with shot number.

So-called hybrid mirrors consists of broadband metallic surface coated with high reflection dielectric multilayer designed for specific wavelength. Such reflectors become more important with progressing development of multiband laser sources realized using parametric down conversion system, in particular for ultrashort-pulsed sources. Multiple pulse picosecond laser induced damage on such mirrors, tested by s-on-1 ISO-compliant method, is important part in development of such components, as there is a need in feedback predicating performance of novel designs. In following paper, we examine laser damage performance of several different designs of silver protected mirrors equipped with HR coating at 1030 nm.

We evaluated laser-induced damage thresholds (LIDTs) on silica glasses by two kinds of ultra-short soft X-ray laser pulses (13.5 nm, 70 fs, and 13.9 nm, 7 ps). The comparison of our experimental results and the reported values observed by nanosecond soft X-ray pulse revealed a pulse width dependence of LIDTs on silica glasses in the soft X-ray region. The relationship between the pulse width and LIDTs provided valuable discussions of the laser-induced damage mechanism.

The continuous wave laser-induced damage thresholds of Amorphous Materials chalcogenide glasses, Amorphous Materials AMTIR-1, AMTIR-2, AMTIR-5, and AMTIR-7 are measured for a 5s exposure of 1.07 μm light focused to a spot size with 1/e² diameter of 830 μm or 1044 μm, following the International Organization for Standardization standards.

Femtosecond laser damage and ablation of various glasses and transparent oxides are studied using time-resolved surface microscopy. We try to understand the damage and ablation mechanisms and how they vary according to their material parameters like bandgap and internal structure.

Virtually all optical materials degrade over time when they are used in high average power or intensity optical systems. Extrapolation of optical components’ lifetime is crucial in such applications in order to avoid downtime or project failure. Measurements of the laser-induced damage threshold (LIDT) fatigue are usually done using the so-called S-on-1 test described in the ISO 21254-2 standard. The standard, however, suggests only rudimentary techniques for extrapolating LIDT, which are rarely used in practice, therefore the goal of this work is to provide a framework for analyzing LIDT fatigue data using well established methods of Bayesian statistics. Numerical S-on-1 experiments (assuming constant fatigue) were performed for cases of online detection, interval detection and offline detection. Appropriate lifetime distributions were determined and used to fit simulated data taking into consideration data censoring. Credible intervals of lifetime predictions were determined using Markov chain Monte Carlo (MCMC) technique and compared with results from multiple experiments. Finally, the Bayesian lifetime analysis method was compared with technique described in the ISO standard for cases of low and high defect densities.

This paper introduces and discusses two analyses key to the design of the proposed US National Standard test for laser damage. These two analyses give the derivation of the requirements on laser fluence profile and spot size. Each of these two design parameters are linked directly to the accuracy of the test. The role of the laser profile is discussed. Specifically, the seminal role of the flat-top profile in ensuring the accuracy of the test result is derived. The implied loss of accuracy and specificity of the test result when a Gaussian beam is used for the test is derived. The second key test design parameter is the spot size which affects the accuracy of the observed rate of damage. The accuracy of the observed rate as function of spot size is derived. Using this formulation rules for the selection of spot size and test length are given. Alternate strategies for observed damage rate corrections, so-called “dead time” corrections, are introduced and discussed.

In the previous year’s work, we have shown that reporting laser-induced damage threshold (LIDT) as a single number might be misleading without mentioning the testing details. Furthermore, we also demonstrated that the longitudinal mode structure of the laser pulse could also lead to some discrepancies in LIDT estimates. A direct comparison of most popular testing protocols, namely 1-on-1, S-on-1, R-on-1, and Raster Scan was made for dielectric mirror coatings. In this year's study, we extended our work to new experiments on transmissive optics, namely uncoated fused silica and AR coatings. As in the previous study we used similar irradiation conditions: both single longitudinal mode injection seeded pulses as well as non-seeded multimode pulses with comparable effective pulse durations. Samples were tested using both first (1064 nm) and third (355 nm) harmonics of nanosecond Nd: YAG laser. In addition to experimental work, we also added a theoretical part that includes the results of pertinent Monte Carlo simulations. The experimental results and simulations are directly compared and discussed.

In this work, an update will be provided on the deployment of shadow cone blockers on NIF grating debris shields. These cones have been demonstrated to reduce the fluence in excess of 11 J/cm2 of an incident 351 nm nanosecond-scale pulse to below the growth threshold of most damage sites. Furthermore, shadow cones will be characterized in terms of their transmission reduction and intensification at downstream surfaces, giving insight into the technique’s broader potential applications and limitations.

An automated set-up for 213 nm UV laser damaging in parallel to spectral analyses will be used to show the spectral laser damaging in silica-based fibers with low hydroxyl content. The 213 nm wavelength is ideal, because it is close to the peak wavelength of one of the E’-centers in silica. Due to automation, short-term measurements down to 0.5 s and long-term measurements up to 2 days and more are possible. In addition, the spectral transmission changes are fitted with multiple Gaussian shaped bands. Although the basic attenuation in non-loaded fibers is high, the pulse energies are still high enough to generate defects along a 1 m long fiber. For the first time, to our knowledge, a transfer from E’γ to E’γ is observed within 1 s, with a laser repetition rate of 2 kHz. Due to optimal fitting, a band around 180 nm is likely influencing the UVC region. In hydrogen-loaded fibers, similar UV defects are seen. The related absorption bands can be optimally adopted to measurement results. The E’-centers play a minor role in short-term measurements because these defects are passivated during hydrogen-loading. Additionally, the band at 328 nm due to molecular chlorine will be reduced. The temporal behavior of all absorption band, including the predicted 180 nm band, are shown.

Recently, ultrashort pulse laser processing has been attracting attention as a method for microprocessing SiC. However, there is a severe problem with this technique: cracks formed around the processed shape hinder precision processing. In this study, to reveal the mechanism of crack formation during the ultrashort pulse laser processing of SiC, we investigated the high-speed phenomena happening during processing. The phenomena were captured using an imaging system consisting of the pump-probe imaging method and a high-speed camera. The ultrashort pulse laser and the high-speed camera are operated at 1 kHz in synchronization, which enables us to capture the high-speed phenomena during processing that change as the process progresses. As a result, we have succeeded in capturing the damage formation process. The results show that the damage is generated and grows only near the tip of the processed hole and does not change once it is generated. As known from previous studies, stress waves propagate around the tip of the processed hole during machining, suggesting a strong correlation between stress waves and damage generation. The larger the pulse energy, the more damage is generated, due to the large stress waves generated because of the large removal volume. When the pulse width is long, the material is thermally affected, and thermal damage is thought to occur at the entrance of the processed hole.

The interaction of ultrafast laser pulses and dielectric materials has been under intensive research for improvement of laser induced damage of optics for high intensity lasers. A 2D model based on Keldysh photoionization and finite-different time-domain (FDTD) algorithm are used to simulate the ionization processes in multilayer interference coatings, taking nonlinear photoionization, impact ionization, and plasma collision into account. Simulation and experimental results of bulk fused silica with different pulse durations and angles of incidence are compared and discussed. We also simulated the interaction of a 40-layer SiO₂/Ta₂O₅ high reflective interference coating designed for 45° angle of incidence and a p-polarized 5-fs pulse at a wavelength of 800 nm, and the damage threshold of the coating is estimated.

Laser-induced damage threshold (LIDT) of dielectric coatings prepared on monocrystalline neodymium-doped yttrium aluminium garnet (YAG) substrates was studied. Various coating designs were prepared using either reactive or ionassisted e-beam deposition technology and tested at 1030 nm 10 ns in r-on-1 mode according to the ISO 21254 standard. Measured damage thresholds were compared and LIDT was discussed with respect to thin-film design and coating technology.

Laser-induced damage threshold decreases when an optic is exposed to multiple laser pulses. In the femtosecond regime, the fatigue of dielectric materials is attributed to incubation of laser-induced lattice states. The goal of this study is to investigate sub-critical damage in a quantitative manner so that the lifetime of single-layer dielectric coatings could be predicted for femtosecond applications. Sub-critical damage was found to consist of localized nanogrooves (100 nm wide, 1-2 um long) oriented perpendicularly to laser polarization. Simple fatigue model was used to simulate fatigue curves which were in good agreement with experimental S-on-1 data for the catastrophic damage.

Indium tin oxide (ITO) films have been widely used in optoelectronic devices, such as solar cells, organic light emitting diodes, liquid crystal devices and so on. The simple and efficient laser annealing technologies have been employed to achieve the desired structure and properties of the films for practical applications. We focus on an 1064nm quasi-CW laser annealing, which is maybe an alternative low-cost choice compared with the current excimer and fs laser annealing. Effects of 1064nm quasi-CW laser annealing on the optical performance, electrical property and chemical composition of the ITO film were investigated in detail in this paper. It was found that the ITO film surface appeared discoloration annealed by 2000 W/cm². Experimental results showed the transmittance of the above annealed ITO film at near-infrared band was improved obviously and the electrical sheet resistance was increased slightly compared with that of the unannealed film. The improvement of the transmission at 1064nm of the annealed film come from the reduction of absorption. The XPS analysis results showed a modification of rations of oxygen and Sn2+ after laser annealing, indicating the reduction of oxygen vacancy and free electrons, were responsible for the optoelectrical property modification of ITO films. However, when the higher annealed laser power density was utilized, the ITO film surface occurred laser-induced cracks. The annealing mechanism was discussed.

Among the fundamental mechanisms of laser-induced damage of optical multilayers, multiphoton absorption is frequently addressed. The two most common models (the fixed-multiphoton-order model and the Keldysh model) of nonlinear absorption are invalid for optical-coating materials at laser fluence close to the LID threshold. An alternative approach is outlined in this presentation that considers a cosine band-structure model. Time-domain simulations suggest that the multiphoton order substantially deviates from its non-perturbed value at the peak of a laser pulse especially in wide-band-gap materials like fused silica. Simulations with the cosine model show that the Keldysh model significantly overestimates the multiphoton order. Based on those results, we discuss a method to correctly evaluate the pulse-averaged order of multiphoton absorption.

The development of advanced laser systems has paved the way for spaceborne laser applications like Earth’s atmosphere and surface monitoring. Prominent technologies like Nd:YAG are often exploited, however they have proven a challenge to combine the different requirements for space missions. High optical efficiencies and tunable wavelength, which are desirable for many applications, can be reconciled with a simple laser design employing Alexandrite crystals. Horizon 2020 project presented here focuses on the development of high quality and high performance coated Alexandrite crystals along with the construction of a laboratory prototype Alexandrite laser system with specifications suitable for Earth observation missions.

In this work we report an experimental investigation of subsurface damage (SSD) in conventionally polished fused silica (FS), sapphire substrates, and YAG crystals which are widely used in laser applications and directly influence performances of critical ultrahigh intensity and high average power laser system optics. Two surface treatment procedures were tested: 1 – plasma treatment, 2 – chemical treatment. Plasma and chemical treatments were applied to fused silica substrates. The laser induced damage threshold (LIDT) FS substrates were studied as the function of etching depth.