During the more than 60 years from the invention of the laser to demonstration of ignition on NIF, scientists, engineers and technicians at LLNL developed incrementally larger and more energetic/powerful laser systems designed for inertial confinement fusion. Each step forward brought new understanding of issues and new concepts for their solution. A continual effort to solve new and often surprising incidents of optical damage supported this evolution. Insights into problems of scale learned from previous lasers, including Argus (1977), Shiva (1978), Nova (1984) and Beamlet (1995) were combined successfully in NIF to provide this platform for the recent ignition demonstration. This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract No. DE-AC52-07NA27344; LLNL-ABS-849703

On December 5, 2022, Lawrence Livermore National Laboratory’s (LLNL) National Ignition Facility (NIF) made history, demonstrating fusion ignition for the first time in a laboratory setting. A review of the major large optic technologies over the past several decades is presented that have enabled the National Ignition Facility laser to both routinely operate >2MJ and achieve fusion ignition.

An optically addressed light valve is described for high-speed laser beam shaping used in rapid metal additive manufacturing [1]. The resulting Area Printing™ delivers shaped high-power pulses to a metal powder bed that locally sinters and melts to consolidate into a fully dense metal part. This technology and device enable scaling, cheaper additive manufacturing with high spatial resolution and greater efficiency with minimal spatter defects. We address here the unique optoelectronic properties and challenges related to optically addressed photoconducting insulator that control the switching dynamics under high intensity laser irradiation. Further description is presented of the device-level thermomechanical analysis from parasitic absorption of the laser at kW to MW power levels. [1] https://www.seurat.com/area-printing

High-energy laser pulses in the nanosecond regime used to be spectrally broadened to mitigate the stimulated Brillouin scattering known to deteriorate the optical elements. Due to propagating effects, this spectrum broadening lead to FM-to-AM conversion, where the UV laser beam experiences an amplitude modulation at frequencies which are harmonics of the phase modulation frequency. We study the impact of the FM-to-AM conversion on the Brillouin backscattering by applying an amplitude modulation on the UV pump laser beam operating at 351 nm and with a 3 ns pulse duration. Experimental measurements show that adding an amplitude modulation frequency on a phase-modulated laser beam could enhance the stimulated Brillouin scattering and lead to laser damage. Thanks to a theoretical and numerical analysis, we show that this singular behavior originates from a resonance between the frequency of the amplitude modulation and the low orders harmonic frequencies of the phase modulated laser beam.

The achievement of laboratory inertial fusion ignition in Dec 2022 required research- and engineering breakthroughs in the areas of optics, lasers, diagnostics and targets. In this presentation, we will give an introduction of the NIF and the fusion experiments performed at this facility and show the progress of the experiments since NIF started operating in 2010, with a focus on the targets. The cryogenic ignition targets need to fulfill stringent dimensional and thermal requirements at 18K. At the heart of the target is the fuel capsule that holds the deuterium and tritium for the fusion reaction. These capsules must be exceptionally pure, round, uniform, and defect-free. We will cover the specifications, fabrication, and technical challenges in manufacturing these capsules.

This conference presentation was prepared for Laser-Induced Damage in Optical Materials 2023.

There has been a concern with the typical Laser-Induced Damage Threshold (LIDT) testing due to the small allowable spot size and the small required tested area. With the current tests, it is possible to actually miss defects entirely, resulting in a higher LIDT value. Experiments conducted in this study compare traditional LIDT measurements in the nanosecond regime made with a broad variant in spot sizes. These same spot sizes are also used to run larger area scans to evaluate the damage sites per area. Experimental results will be presented and discussed in the broader scope of developing a reliable LIDT standard.

Atomic layer deposition offers unique advantages compared to more classical PVD coating processes. These advantages include an inherently high coating thickness homogeneity and conformal coating of both micro-optical structures, such as gratings, and large free-form optics, such as aspheric lenses. The talk will introduce the coating process, compare its properties to those of more classical PVD processes and give an overview of recent developments of ALD coatings in optical applications.

Spallation effects caused by shock waves in optical components such as those used in the Laser MegaJoule facility during laser operation can lead to material fracture. One solution could be to use a viscoelastic thin film on these fused silica components to reduce the reflection of shock waves from the rear surface, but it must have excellent optical, mechanical, and power-handling properties. Among the viscoelastic materials investigated were Nafion and polydimethylsiloxane-based ormosil, with ormosil synthesized using a sol-gel process. The materials were characterized optically and especially tested for acoustic attenuation. These materials, as thin films deposited on a fused silica substrate, were studied under shock wave propagation using the laser shock technique. Preliminary results showed that these thin films have interesting properties that could help reduce mechanical damage to optical components.

Here we present a side-by-side comparison of LIDT of dispersive mirror at a central wavelength of 1030 nm produced via MF magnetron- and RF magnetron- sputtering deposition methods. We have use different layer materials like Ta2O5, HfO2, SiO2. All dispersive mirror provides -200 fs2 in wavelength range 930-1120 nm. The dispersive mirror with Ta2O5/SiO2 has LIDT about 0.12J/cm2. Alternating of HfO2/SiO2 has allowed us to improve LIDT up to 0.2 J/cm2 at 1030 nm, 190fs, 1kHz, in vacuum.

ASML is the leading provider of lithography equipment in the semiconductor industry. Lithography is one of the cornerstones on which todays semiconductor technology is built. It’s a journey that started with Moore’s law in the 60’s and has continued until today and will continue in the future. In the latest generation of technology a high power 30kW CO2 laser is used to ignite a tin plasma that emits 13.5nm photons to enable the printing of 7nm and below linewidths. This keynote address will give a small ‘sneak peak’ into what technology enables todays EUV chip manufacturing industry. It will also highlight some of the Laser Optics damage challenges we have with the high power CO2 laser ASML uses. The presentation will also show some of the theoretical understandings on laser damage that were built up along the way and illustrate where there are still some challenges ahead.

Recent studies suggest that fatigue effect in dielectric optical coatings is possibly associated with the presence of strong nonlinear absorption, however, up to now there was only indirect evidence for such hypothesis. One of the reasons for that was a technical rigor to characterize nonlinear absorption losses in optical coatings and a lack of pertinent experimental data. Recent advancement of common-path interferometry and LIDT testing allows us to overcome such limitations. In this study we examine nonlinear response and fatigue effect in single- and multilayer dielectric coatings below single shot damage threshold. Although there is no quantitative model that could predict fatigue from absorptance, we found an interesting correlation between nonlinear absorption and fatigue effect under comparable experimental conditions. These results help us to understand the mechanism of fatigue in optical coatings and possibly make more durable femtosecond optics.

Optomechanics and surface residues can be sources of contaminants when directly illuminated or subjected to laser scatter, which can then deposit and grow on optical surfaces leading to transmission loss over time. To extend the useful lifetime of laser systems and laser optic assemblies, it is necessary to determine best practices in material selection and handling of components both in and out of the beam path. We present lessons learned from a series of month-long (~100 trilllion shots) experiments performed at 355nm with laser parameters relevant to material processing and research (20ns pulsed ~1kW/cm^2 average). Laser-induced surface contamination and transmission losses of an assortment of optics in controlled and uncontrolled environments were monitored, and contamination mitigation techniques qualified by transmission measurement and microscopy.

The long-term performance of high-power laser systems is adversely affected by particle contaminants that are introduced into the system during the manufacturing of optical components and the handling during installation and operation of the laser system. Such particles can absorb or focus laser energy, reducing the laser-induced–damage threshold (LIDT) values. We developed ultrathin coatings that can decrease the overall load of contamination and aid with the removal of the already-accumulated particles using simple gas-flow cleaning. These coatings do not alter the intrinsic LIDT values, and they remain stable over time and during the system operation.

The National Ignition Facility (NIF) is intentionally operated with the final fused silica glass (SiO₂) optics exposed to fluences and intensities with the potential to induce damage that will grow with additional laser exposure. Therefore, the NIF operates a recycle loop to refurbish final optics by mitigating any initiated surface damage to arrest its growth. However, the morphology of filamentary damage, caused by local self-focusing in the bulk of a silica optic, adds additional complexity to optics mitigation and provides a limitation to optic reusability. This study evaluates techniques for mitigating isolated and clustered filamentary damage. Optical microscopy before and after NIF installation was used to determine the efficacy of filamentary mitigation after a series of high fluence and intensity laser exposures. The challenges and success rate of the methods are compared for various filamentary damage mitigations strategies.

This work explores reactive ion etching parameters in order to identify and optimize key characteristics in gratings that govern their overall performance, including minimization of sidewall and trench structural defects and modification of fused silica via intrinsic molecular-level defects. This study is performed using grating-like samples with 5-µm-wide lines and trenches generated in fused silica by the photolithographic process and inductively coupled plasma-reactive ion etching. The analysis compiles metrology, simulation, and damage-testing results to obtain a better understanding of how to modify the fabrication process of gratings toward achieving better laser-induced–damage performance.

For pulse lengths between 1 and 60 ps, laser-induced modifications of optical materials undergo a transition from mechanisms intrinsic to the materials to defect-dominated mechanisms. Elucidating the location, size, and identity of these defects will greatly help efforts to reduce, mitigate, or eliminate these defects. We discuss our work that detailed the role of defects in the ps laser-modifications of SiO2 and HfO2 1/2-wave coatings. For HfO2 coatings, we included a study of environmental effects on the damage process. We found that the response of defects very near the surface are dependent on the environment, leading to worse damage in vacuum than in air. One or more constituents of air, most likely oxygen and/or water, suppress or lessen the effects of these defects during laser exposure. We discuss the implications of these findings for defect-driven laser-induced damage for ps to ns laser pulses and for mechanisms for laser-induced damage initiation.

Understanding the physical mechanism behind the laser-induced damage of multilayer dielectric interference coatings is essential for developing ultra-high intensity laser systems. The previous work reported high damage thresholds of MLD mirrors and blister formation near the threshold. Here, we present the cross-sectional study of the blisters using transmission electron microscopy and focused ion-beam processing. The measurement shows evidence of void formation and phase transformation under the surface, interdiffusion, and intermixing at the interfaces. These findings provide valuable insights into the mechanisms behind laser-induced damage, facilitating the development of more robust and reliable optics for high-power laser applications.

Stacks of amorphous oxide mixtures and SiO2 conform the interference coatings of current gravitational wave detectors (GWD). This talk will discuss a comprehensive study of amorphous oxide mixtures and nanolaminates that has led to the identification of a new alloy, TiO2 doped GeO2 which is a promising material to engineer next generation coatings for gravitational wave detectors with lower coating thermal noise.

Quantization effects in nanolaminate structures of oxide materials were proposed and experimentally demonstrated only recently. In this paper we will investigate the material combinations of Ta2O5-SiO2 and amorphous silicon-SiO2 deposited by magnetron sputtering and show that the quantization effect is observed in both materials. We will describe the deposition process and demonstrate the tunability of the refractive index and the bandgap energy. Quantized nanolaminates (QNL) composed of Ta2O5-SiO2 in combination with SiO2 were used as high and low refractive materials in optical interference coatings forming an antireflection and a mirror coating, whereas QNL with aSi-SiO2 as the high index material were used in a log pass filter with edge at 720nm. All designs could be deposited successfully with close match to the design. The aSi-SiO2 based filter showed a blocking range throughout the visible spectrum whereas a comparable filter based on SiO2-TiO2 only blocked 500-700nm.

In our recent experiment, it is discovered that the interaction of resonant metasurfaces and mid-infrared femtosecond laser pulses can realize damage patterns that overcome this limitation, and the geometry of the trench can be controlled by the pulse intensity, polarization, and the total pulse number. In this study, we report the particle-in-cell (PIC) simulation of the interaction of the M-shape metasurface and 200-fs mid-IR laser pulses with high intensity. The simulation results suggest that localized lattice heating and explosions occur at a scale and in the relationship with the polarization consistent with the experimental data.

Ultrafast lasers are very useful for surface engineering of semiconductors. Here we used a Scanning Tunneling Microscope (STM) to map in situ topography and spectra of hydrofluoric acid-etched silicon (100) damaged by an ultrafast pulsed Yb:KGW laser at 1030nm with 70fs duration in high vacuum. We observed absence and presence of laser induced periodic surface structures with single and multiple shot irradiation, respectively. Surface morphology were captured with atomic resolution, which can help understand the subtle changes to surface ultrafast lasers can cause near the laser induced damage threshold fluence. The results demonstrate the potential of STM for in-situ studies of laser damage on clean surfaces in ultra-high vacuum.

We investigate the unique surface fractures of CaF2 found after single shot laser irradiation using 77 femtosecond, 1030 nm laser pulses. Optical microscopy and atomic force microscopy revealed elevated rectangular structures across laser-ablated craters. The underlying mechanism for this unique morphology may be related to anisotropic thermal conductivity and laser-induced defects. Our findings provide insights into the fundamental mechanisms of laser-induced damage in CaF2 and have implications for the design and optimization of high-power laser systems.

A unique dual-beam laser-damage test station has been constructed for testing materials with broadband incoherent radiation. Utilizing a novel optical parametric amplifier-based light source capable of delivering an incoherent bandwidth of up to 10 THz, bulk damage in KDP has been characterized for a number of different bandwidth conditions to help understand the role that the resulting intensity fluctuations play. The results largely suggest that damage mechanisms in KDP do not rely heavily on nonlinear processes and are supported by established models of plasma generation and growth.

Possible linear-to-circular polarization conversion had been studied for the Laser MégaJoule. We measured the consequences of such polarization conversion on laser-induced damage using the MELBA testbed. The MELBA laser is located in CEA CESTA (France) and delivers a nanosecond UV centimeter-sized laser beam. Experimental comparison of polarizations states showed a significant decrease of damage densities in circular polarization. Thanks to the particular imaging setup, we were able to explain this by both a reduction of the Kerr effect (supported by theory) and a reduction of the intrinsic absorption of silica optics defects.

In this work we present a novel approach to filling damage sites close to the surface. We explore laser parameters and thermal distribution for material reflow.

Our study analyzed the laser-damage threshold of liquid crystal alignment materials, including photoaligned azobenzene, rubbed polyimide, and rubbed nylon. We found that the presence of liquid crystal was necessary to observe variation in damage thresholds among alignment materials. Nylon outperformed photoalignment, which outperformed polyimide. We also investigated the polarization dependence of the damage threshold in ordinary and extraordinary modes at a near-infrared wavelength and found that only the photoalignment material demonstrated polarization sensitivity at our statistical power level. Our results can inform the design of high-power beam-shaping devices for various applications, including fusion, 3-D printing, and defense systems.

This conference presentation was prepared for Laser Damage, 2023.

This conference presentation was prepared for Laser Damage, 2023.

This conference presentation was prepared for Laser Damage, 2023.

This conference presentation was prepared for Laser Damage, 2023.

This conference presentation was prepared for Laser Damage, 2023.

Nonlinear index of refraction is of great importance in evaluation of laser-induced damage threshold, as it relates to parameters defining self-focusing critical power and avalanche breakdown. An accurate method to measure the nonlinear refraction can help restrict the damage caused by these mechanisms. Beam-Deflection (BD) method is a useful tool to calculate nonlinear refractive index. The critical parameters in the calculations are probe-to-excitation spot size ratio, r, and the relative displacement of the two overlapping beams. Similar to the Z-Scan method, an empirical function, solely dependent on r, is obtained which provides a relation between the BD signal and the phase shift.

High diffraction-efficiency nonpolarizing gratings with CW damage thresholds in the range of 100 kW/cm² and higher are necessary for scaling Spectral-Beam-Combined (SBC) High-Energy Laser (HEL) systems to MW powers and above. We present the results of a campaign to improve capabilities of multilayer dielectric gratings for these applications. Current capabilities are demonstrated by showing the peak temperature, damage threshold, defect density, and diffraction efficiency (where applicable) of 51 MLD gratings and 17 coatings when illuminated at 1070 nm at intensities up to 3 MW/cm².

This conference presentation was prepared for Laser Damage, 2023.

This conference presentation was prepared for Laser Damage, 2023.

This conference presentation was prepared for Laser Damage, 2023.

This conference presentation was prepared for Laser Damage, 2023.

Glass drilling and cutting is crucial for optics, consumer electronics, and Micro-Electro-Mechanical System (MEMS) devices. Speed and reproducibility are issues common to traditional glass cutting methods. We use a femtosecond laser to efficiently and accurately cut interior shapes in glass. Unlike a traditional Gaussian beam, which has a shallow focal range and cannot penetrate deep into materials, Bessel beams have a much longer focal range, up to millimeters. With a Bessel beam, we can cut straight through without the need for mechanical cleaving or moving the sample through the focus, improving reproducibility and speed. The cut surfaces are analyzed with optical microscopy, atomic force microscopy, and scanning electron microscopy to observe any structural/morphological changes to the materials near the laser affected regions. Our 260fs laser operates at 10kHz, with 1030nm central wavelength, depositing 1.4W on target. An axicon generates the Bessel beam with a FWHM central spot size of 6±1µm and a fluence of up to 41Jcm^-2. Our study has the potential to open new technological pathways for integrated electronic and photonic platforms.

This conference presentation was prepared for Laser Damage, 2023.

This conference presentation was prepared for Laser Damage, 2023.

This conference presentation was prepared for Laser Damage, 2023.

This conference presentation was prepared for Laser Damage, 2023.

This conference presentation was prepared for Laser Damage, 2023.

This conference presentation was prepared for Laser Damage, 2023.