In this study, we explore the non-linear absorptance properties of Ta2O5, HfO2, and SiO2 oxide coatings when subjected to intense laser irradiation. Employing common path interferometry (CPI) in combination with intense laser pulses at 1064 nm (10 ps), we investigated both single- and multi-layer coatings. Surprisingly, HfO2 and SiO2 coatings exhibited almost negligible nonlinearity, while Ta2O5 layers displayed rather significant non-linear behavior. Despite the assumed 3-photon absorption process estimated from photon energy and band gap relations, our observations indicate a prevalence of 2-photon absorption in Ta2O5 layers. These findings carry significant implications for comprehending the performance of multilayer optics, especially dispersive mirrors, under conditions of high intensity.

We demonstrate efficient anti reflection coatings based on adiabatic index matching obtained via nano-imprint lithography. They exhibit high total transmission, achromaticity (99.5% < T < 99.8% from 390 to 900 nm and 99% < T < 99.5% from 800 to 1600 nm) and wide angular acceptance (T > 99% up to 50 degrees). Our devices show high laser-induced damage thresholds in the sub-picosecond (>5 J/cm 2 at 1030 nm, 500 fs), nanosecond (>150 J/cm 2 at 1064 nm, 12 ns and >100 J/cm 2 at 532 nm, 12 ns) regimes, and low absorption in the CW regime (<1.3 ppm at 1080 nm), close to those of the fused silica substrate.

The damage initiation and damage-growth behavior of dielectric mirrors suitable for operation in the ultraviolet (351-nm) spectral range is investigated as a function of the dielectric materials involved, optics design, beam polarization, and pulse duration. The aim of this effort is to understand the optimal designing parameters of transport mirrors for nanosecond pulses in the near-ultraviolet spectral range. The results provide insight into processes that affect the damage-growth resistance resulting from material modifications during damage initiation.

Hafnia, a main optical material in high-energy laser applications, faces limitations due to precursors prone to laser damage. Addressing these precursors is critical to producing laser-resistant films. Nanobubbles within hafnia layers contribute to laser damage upon UV, nanosecond-laser exposure. This study examines hafnia film deposited by ion beam sputtering with different working gases, either Argon or Xenon. The effect of nanobubble size, which varies according to the working gas used, on the film performance under nanosecond-laser irradiation was investigated. The results indicate that the different nanobubble sizes influenced by the working gas affect the laser damage mechanism.

Understanding the response of wide-bandgap materials such as silicon dioxide (fused silica, α-quartz) to light is crucial for achieving precise control and manipulation in ultrafast laser volume structuring at the nanoscale. Surpassing optical resolution, this scale of achievement necessitates manipulating light energy around bulk inhomogeneities while precisely orchestrating selective thermodynamic pathways for absorption confinement, crystal-amorphous transformation and rapid energy quenching within nanometer lengths. We propose multiphysics calculations to elucidate the intricate interplay between electronic structure alterations and structural/hydrodynamical relaxation mechanisms under extreme nonequilibrium conditions. In particular, ab initio calculations reveal a narrowing of the bandgap by several eV and a loss of cohesion within an ultrashort timescale. This approach enables precise control and manipulation, optimizing processing parameters, and exploring novel aspects of solid relaxation induced by intense photoexcitation.

The ultrahigh-intensity laser systems are crucial to various applications such as particle acceleration and research of extreme conditions. Therefore, a higher laser induced damage threshold (LIDT) of optical components is demanded. To study the mechanisms of the ultrafast laser-solid interaction, the modeling is important. Traditional modeling of ultrashort laser-solid interaction is based on Finite-Difference-Time-Domain (FDTD) that can only reveal the electromagnetic field distributions. However, Particle-in-Cell (PIC) simulation can reveal both the field distributions and the particle dynamics. We used and modified EPOCH with Keldysh photoionization and a model for a spatially varying permittivity to capture the thermalization of the electrons and the plasma generation in a multi-layer dielectric mirror irradiated by a few-cycle pulse and predict the LIDT. The modeling work can provide guidance on designing and manufacturing of the optical components.

Few temperature-dependent experiments exist for laser damage studies, yet temperature greatly influences material behavior and response to laser irradiation. This study examines the effects of cryogenic temperatures on femtosecond laser-induced damage of copper, chosen for its well-defined thermal properties. Using a 77fs, 1030nm laser at normal incidence, we tested single crystal copper at temperatures ranging from 20K to 350K, in vacuum in a cryostat. Results indicate that lower temperatures increase damage thresholds by 20% from 300K to 25K. Optical and Atomic Force Microscopy reveal underlying mechanisms, complemented by modeling. This research furthers understanding of laser damage physics and strategies to enhance optical damage thresholds in high-power laser systems.

Many mechanisms can follow laser absorption in wide band gap materials. Polarons are electronic excitations that self-trap by distorting local ionic structure and can increase the likelihood of subsequent laser absorption and damage. We present ultrafast time-resolved imaging and Density Functional Theory (DFT) results on polarons in multi-component glass compositions. Proper accounting for polaron phenomena is important for modeling of ultrafast laser processing, understanding electronic conduction in glasses and related materials and fundamental understanding of precursor mechanisms to optical damage.

Sapphire is a robust dielectric material with many applications in lasers and optical systems. It is widely used in a doped form as a laser gain medium or undoped for optical windows. Past work indicated similar laser-induced–damage behavior compared to fused silica, arguably owing to their similar relevant thermomechanical properties. We have studied laser-damaged sapphire through Raman spectroscopy and fluorescence-based piezo spectroscopy. These techniques provide new understanding related to the relaxation of the material following laser damage and quantification of the residual stress in the laser-modified region.

Optical and photoluminescence 3D imaging of small fused silica laser-induced damage sites allows us to understand the damage growth mechanisms. The laser damage growth process is driven by local absorption centers and its location and depth are the key factors. To quantitatively extract the factors from the 3D multi-modal image data set, various metrics are obtained by image analysis techniques and evaluated. We believe that our measurement and analysis approach can allow rapid identification of growth-prone damage sites, providing a pathway to fast, non-destructive predictions of laser-induced damage growth and enable selective damage site mitigation. 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-ABS-863515

Over time, optical components tend to degrade, potentially leading to reduced performance or even system failure. This consideration extends beyond technical concerns, impacting the economic, operational, and reputational aspects of various systems and industries. Ensuring a long lifetime for optics is crucial for maintaining consistent performance over extended periods. Thus, estimating the lifetime of optics is particularly significant in the context of long-term operations involving high repetition rate laser systems operating in ultrashort regimes or UV spectral wavelengths. However, accurately estimating optics lifetime for real-world applications poses a significant challenge due to the lack of appropriate methods or their accuracy. Furthermore, understanding the physical mechanisms behind the lifetime is essential for optimizing optics performance. To address this need, we conducted a study investigating the absorption effect on the lifetime of dielectric coatings. Using the photothermal common-path interferometry and laser-induced damage threshold testing, we sought to identify possible correlations between the nonlinear absorptance of optical coatings and their lifetime.

We present the ELAN testbed, which aims at assessing laser-induced damage of thick and large silica optics for the Laser Megajoule (LMJ) facility. A custom and patented injection seeding system was implemented on our Nd:YAG laser: this allows us to use phase modulated pulses to annihilate backward stimulated Brillouin scattering during tests while guaranteeing a smooth temporal profile. Then, beam propagation simulations of the incident spatial profile with Miro code (CEA) allows us to correct for the surface narrowing of the beam on the exit face of the optic due to Kerr self-focusing. This testbed allows us to test LMJ 34 mm vacuum window at 351 nm in nanosecond range with fluence up to 30-35 J/cm² with a control of non-linear propagation effect.

The National Ignition Facility’s (NIF) final fused silica optics are regularly exposed to fluences that initiate and grow surface damage during high-energy operation. This mode of operation is enabled by regularly recycling the optics to mitigate the initiated surface damage. Mitigation consists of removing the fractured material associated with the damage by ablating a conical void into the fused silica substrate using a CO2 laser. Applied mitigations, which are generally robust to the highest fluences present on the NIF, can fail due to a variety of manufacturing imperfections. After multiple recycles, final NIF optics regularly have >1000 mitigations present and therefore even low rates of mitigation failure can be detrimental to an optics operational lifetime. Furthermore, the quantity of mitigations makes it challenging to identify all instances of mitigation failure. This work details the creation of an automated system that inspects mitigations for damage and the failure analysis of mitigations fielded on the NIF. >100,000 unique mitigations were inspected, enabling a high resolution understanding of the failure rate and providing detailed information as to potential failure

Relatively thick (>1-um) organic-polymer coatings with a large resistance to laser-induced damage at UV wavelengths are desired for new inertial confinement fusion laser optics under development at the Laboratory for Laser Energetics. These optics include surface-figured, KDP polarization rotators and actively cooled laser glass. Organic-polymer materials, however, are generally known to have a low laser-induced–damage threshold (LIDT) in the UV, particularly as it pertains to multipulse applications. In this work, we present the single-pulse and multipulse LIDT results for thick (>1.5-um) polymethacrylate films deposited on fused silica and cured at different temperatures. The results demonstrate that it is possible for thick polymer films to withstand thousands of pulses at fluences higher than their single-pulse LIDT counterpart. In fact, in some test sites, the underlying fused silica substrate suffered exit surface damage before the polymer film could be damaged. These results and a discussion of the underlying mechanisms responsible for this behavior will be presented.

The near-infrared, laser-induced damage performance of a broadband, antireflective metasurface optic was measured at five different pulse durations, ranging from 1.4 ns to 20 fs. Analogous measurements were performed on an equivalent bare fused silica substrate which did not receive metasurface treatment. Results showed that the damage threshold of the metasurface was about 30% to 50% of the first-surface damage threshold of the untreated substrate (exit-surface damage was not considered). The resulting morphologies are investigated with scanning electron microscopy. The goal of this work is to investigate the feasibility of metasurface optics in short-pulse, high-peak-power laser applications.

The development of optics that provide spatial control of birefringence could enable better control of laser beam polarization, but available solutions are limited. Here we demonstrate a method to locally modify the birefringence of waveplates fabricated by glancing-angle deposition. The method employs localized melting of the anisotropic microstructure and we demonstrate that this process is only possible under high vacuum. The direct-write method presented here can be readily utilized for coatings exhibiting form birefringence of virtually any chemical composition, size, and format. The associated material modifications are characterized using an array of tools.

Polarization smoothing is an important method used to improve beam uniformity and on-target energy coupling during inertial confinement fusion experiments. First-generation polarization smoothing optics deployed in the ultraviolet section of the 60-beam OMEGA Laser System are based on potassium dihydrogen phosphate (KDP) wedges, which produce two diverging, orthogonally polarized beams. An upgrade to a random continuous polarizer (RCP) wave plate is desired that calls for an arbitrary distribution of polarization states. Imprinting a freeform depth profile into a birefringent crystal such as KDP is a promising approach for fabrication of a large-aperture RCP. Modern optical fabrication technologies are capable of imprinting these designs; however, the challenging material properties of KDP require new innovations in process and slurry chemistry. This presentation will discuss recent advances in our efforts to fabricate a KDP-RCP.

We design, fabricate and measure transmissive dielectric metasurfaces made of high-aspect-ratio, wide-bandgap oxide materials to achieve λ/4 retardance at deep ultraviolet wavelengths. We optimize the design towards a broadband quarter-wave plate for ultrafast pulses while being resistant to high-power lasers. We also test the damage threshold of the fabricated metasurfaces to evaluate the efficacy of various oxide materials in comparison to each other and bulk conventional optics. Our work could pave the way towards further development of transmissive DUV optical elements with customized functionalities and their integration into more complex systems for spatiotemporal shaping of DUV pulses.

We demonstrate the versatility of dielectric metasurfaces in arbitrarily controlling the full four-dimensional properties of ultrafast pulses, and discuss opportunities of their use with high-energy lasers.

Mesomorphic ceramics are inorganic solids with anisotropic superstructures that are derived from lyotropic suspensions. Here we report on the synthesis of amorphous silica nanotubes and their subsequent processing into mesomorphic ceramic thin films. Nanotube synthesis involves the formation of nickel hydrazine complexes within inverse micelles followed silica coating and etching of the core. A lyotropic suspension of silica nanotubes is formed and subsequent blade-coating results in birefringent thin films. Sintering of particle assemblies may result in waveplates with high laser damage resistance.

We will present advances of metasurface fabrication which enable substrate-engraved antireflection surfaces and birefringence elements. Large-beam 351 nm laser damage performance of designer metasurfaces fabricated for antireflection applications will be discussed. We will also present fabrication technology that has helped pave the way toward subwavelength quasi-linear all-glass metasurface gratings for quarter waveplate application at 351 nm.

Twenty-five years after the discovery of anisotropic nanostructures in silica glass created by laser writing with polarized ultrashort light pulses, the physics and applications of the resultant form birefringence remain a significant area of interest. By controlling the polarization azimuth, it is possible to directly write flat optical elements with spatially varying birefringence, utilizing the geometrical or Pancharatnam-Berry phase. This technology is particularly applied in S-waveplates for polarization beam shaping, with applications ranging from material processing to optical trapping and generating extreme UV vector beams. More recent developments have led to ultralow-loss birefringent optical elements such as UV retarders, geometrical phase lenses, and prisms, created using a novel anisotropic nanoporous modification in silica glass, known as Type X. These elements demonstrate high transmission in the UV range and damage thresholds comparable to pristine silica glass, making them particularly valuable for polarization control in high-power laser applications.

Mitigation of laser-induced surface damage sites on fused silica components is critical for reliable and cost-effective operation of Inertial Confinement Fusion lasers such as the National Ignition Facility in the USA or the Laser MégaJoule in France, or the Shen Guang in China. CO2 laser processing has proven to be an effective technique for laser-damage mitigation on large aperture silica optics. Here, we present a quantitative and comparative study of mitigated damaged sites ablated with different laser spot sizes ( 400 µm to 100 µm) and with parametric variations on pulse repetition rate and pulse fluence. We focus on the laser processing parameters required to reduce negative effects such as surface deformation, residual stress, debris formation, or rim formation, and compare their performance regarding optical damage initiation. Numerical simulations based on commercial software COMSOL-Multi-physics are used to have a better insight of the thermo-mechanical dynamics occurring during the laser processing of fused silica, and as guidance to improve the mitigation process.

Storage Ring FELs are one of the primary sources for circularly polarized γ-radiation in various experiments. The achievable energy of this γ-radiation is strongly related to the central wavelength of the UV wavelengths in the FEL. This lasing wavelength, in turn, is determined by the VUV-resonator mirrors, which face a unique set of requirements, including high reflectivity of 94% for a protected system and low losses at a wavelength of 155 nm and below, as well as resistance to intense VUV and γ-radiation. The contribution will show the manufacturing, laser damage caused in the FEL, and damage mitigation strategies.

Laser-induced damage is typically a limiting factor in the design of ultraviolet nanosecond highenergy laser systems. Efforts over the last 10+ years have resulted in significant improvements to laser-induced damage resistance of fused silica by removal of damage precursors historically left by several steps in the fabrication process. However, by enabling optics to operate at higher energy densities, new challenges have emerged. Fused silica, when exposed to high-energy laser light (without inducing damage) can degrade the damage robustness of adjacent surfaces. It is hypothesized that vaporized SiOx particles from the first laser exposure recondense onto surrounding surfaces acting as local absorbers which can initiate damage upon future exposure. We show that modifying the fused silica surface using either chemical or thermal treatment can significantly alter the magnitude of the degradation. Finally, we develop two hypotheses that can explain the reduction in observed surface degradation.

As the demands of high repetition rate, high intensity laser applications rise, robust interference coatings are needed that can balance the conflicting requirements of a strong laser damage threshold, high reflectivity/transmissivity, and low group delay dispersion. Two layer anti-reflection coatings (Air/SiO2/HfSiO/substrate vs Air/SiO2/Hf-SiO2 nanolaminates/substrate) were tested with p-polarized, 77-fs 1030-nm laser pulses. Both coatings had identical refractive index at 1030-nm for the high index layers, but one coating contained a ~200-nm thick layer of mixed HfO2 and SiO2, while the other had a nanolaminate featuring 25 pairs of <5-nm HfO2 and SiO2 layers. Nanolaminate performance under femtosecond irradiation is relatively unexplored; this work aims to address that, and shows the damage threshold fluence of the nanolaminate sample was ~2/3 of that of the mixed layer sample. These results set the stage for developing stronger nanolaminates for femtosecond pulses.

Dielectric coatings are ubiquitous in the field of laser optics, and serve a wide range of needs including beam transport and polarization control. While much attention is paid to their optical properties and interaction with light, their mechanical properties are of importance in understanding modes of failure and environmental stability, and are an integral part of material modifications following laser-induced damage. In fact, the damage morphology of coatings encompasses information about the mechanical properties of coatings that can reveal failure mechanisms. In this work, we study nanosecond laser-damage sites in electron-beam–deposited coatings with alternating layers of hafnia and silica. The results show a consistent pattern of separation between layers of silica deposited on hafnia, indicating that the adhesion strength of hafnia deposited on silica is higher to that of silica deposited on hafnia. A number of mechanical strength testing methods have been employed in order to help understand this discrepancy between adhesive strengths between two interface types in the same pair of materials. Pull-off tests performed on bilayer coatings show adhesion strengths of all interfaces are in excess of 6 MPa, and adhesion between a number of liquid-based adhesives and coatings is shown to be greater when applied to hafnia. The effect of each coating type on the fracture strength of silica substrates is demonstrated to be minimal through a series of ring-on-ring stress tests. Results of indentation and scratch tests covering a range of applied stresses will be covered as well. We postulate that the origin of this behavior is related to the columnar structure of the as-deposited hafnia layers and the resulting surface roughness.

This study examines the damage threshold of poly(methyl methacrylate) (PMMA) nanostructures when exposed to high-intensity mid-infrared (MIR) light. U-shaped PMMA nanostructures were arranged on a CaF₂ substrate, with resonant frequencies identified between 1724–1730 cm^-1 using FTIR and AFM-IR, corresponding to the carbonyl (C=O) stretching vibration. A femtosecond laser at a 10 kHz repetition rate delivered 180 fs pulses with 9 µJ per pulse and a 100-micron spot size, resulting in rapid damage to the nanostructures. Findings suggest that both resonant absorption and cumulative thermal effects contributed to damage. Future work will explore single-shot pulses and varying intensities to better understand the interplay of resonant absorption and thermal damage, aiding the development of advanced materials for high-intensity MIR applications.

Absorption is a key parameter for optical materials and coatings in an increasing number of applications. Following the need for absorption measurements, a variety of different techniques have been established in the past 2 decades. Although all of them are very sensitive - allowing to measure down to the ppm absorption level – the absolute calibration remains a main challenge. For the first time to the best of our knowledge, we present data of a Round-Robin absorption test with a total of 11 participants using 5 different measurement techniques, including scientific institutes as well as companies. The subject of the test is the measurement of two highly reflective (HR) coatings (Bühler Alzenau GmbH) with different expected absorption levels at a wavelength around 1064nm. Besides a look on the overall absorption data scattering, the goals are comparing data obtained by identical test equipment at different locations as well as the influence of sample cleaning procedures. Additional CRD, total scattering, and residual transmission measurements provide information on the expected absorption data.

Ultra-intense laser systems in the long-wavelength infrared (LWIR) spectral region have opened doors to new physics in accelerator research, primarily due to favorable quadratic scaling of the ponderomotive potential with the laser wavelength. Although there is a growing demand for higher peak-power in ultra-fast laser science, its progress is limited by the onset of nonlinear optical effects and laser-induced damage to optical components, which can degrade laser performance. Numerous studies have explored these properties in the ultra-violet to mid-infrared wavelength range using ultra-short-pulsed lasers, but their manifestation at longer wavelengths remains under explored. Consequently, there is a lack of reliable data on materials’ nonlinear properties and laser damage thresholds under ultra-short LWIR pulses near a 9 µm wavelength. This research presents preliminary damage threshold measurements for selected transparent LWIR laser optics and mirrors. Experiments were conducted in air for high-peak power 9.2 µm laser pulses with durations switchable between 2 ps and 70 ps. Samples were characterized ex-situ using optical microscopy to estimate the damage areas, which scale linearly with the logarithm of pulse energy for near-Gaussian beams. Observations reveal distinctive damage thresholds and morphologies caused by the two pulse duration regimes, with no clear scaling with the laser pulse width due to sample-to-sample variations. This laser-induced damage data is crucial for the design of future laser sub-systems such as post-compressors and contributes to the fundamental understanding of material responses to ultra-intense LWIR laser pulses.

Fatigue, also known as optical component aging, is the gradual reduction in LIDT caused by a high number of laser pulses that are not powerful enough to cause initial laser damage. The duration of the laser pulse, as well as its wavelength, affects the resistance of the coating to laser-induced damage, especially at shorter pulse durations and lower wavelengths. This study’s aim was to evaluate dielectric IBS, IAD, and EB-coated UV mirrors operating in the single ps pulse regime and to define the key features that contribute to the aging of the component. For this purpose, laser-induced fatigue damage testing was completed at 343 nm wavelength using the S-on-1 procedure with single ps pulse duration by a laser system operating at a repetition rate of 200 kHz, with up to 10 million pulses per single site. LIDT values for two distinctive damage types were defined based on the observed changes in the sample: catastrophic failure and color-change modes. Subsequently, coatings with different spectral characteristics, surface properties and structural features were evaluated and their laser-induced fatigue damage results were compared.