This PDF file contains the front matter associated with SPIE Proceedings Volume 12300, including the Title Page, Copyright information, Table of Contents, and Conference Committee Page.

This year’s competition proposed to survey the damage resistance of near-IR high reflectors designed for continuous-wave (CW) laser applications. The requirements for the coatings were a minimum reflection of 99.5% at normal incidence for 1077-nm light. The participants in this effort selected the coating materials, coating design, and deposition method. Samples were damage tested at a single testing facility using a kW fiber laser source capable of delivering up to 10 MW/cm² peak irradiance on target. A double blind test assured sample and submitter anonymity. The damage performance results, sample rankings, details of the deposition processes, coating materials and substrate cleaning methods are shared. We found that multilayer coatings using tantala or hafnia as high index materials were top performers under CW laser exposure within several coating deposition groups. Namely, dense coatings by ion-beam sputtering (IBS), plasma-enhanced atomic layer deposition (PEALD) and magnetron sputtering (MS) exhibited the lowest absorption & temperature rise upon CW laser irradiation without damage onset up to the maximum power density level available in this study.

Laser-Induced Deep Etching (LIDE) is considered as the one of the most promising techniques for production of so-called TGVs (Through Glass Vias). In the production process, thin glass sheet is treated with ultra-short lasers pulses to induce surface and volume modification, allowing efficient wet etching and formation of through hole. Precise knowledge of damage threshold of such glass is essential when optimizing the whole process and scaling up the production via laser beam parallelization. In following paper, we present recent results on LIDT measurement of D263 glass sheets at wavelengths 1030 nm and 515 nm, effective utilization of such knowledge for setting up multi-Bessel beam processing optics, and we demonstrate resulting substrates with TGVs.

We present the development of carefully tailored shape - increased size (0.9 mm diameter) input surface mitigation sites that shadow and thus supress damage growth on the exit surface of optics. Results from downstream intensification measurements and laser induced damage experiments are presented. The results show a 6X reduction in expanding wave intensification on the exit surface of an optic, being the dominant damage onset mechanism. The tailored rounded cone design can withstand over 30 J/cm² sub aperture input surface fluence. A significant decrease in laser induced damage initiation and growth was observed compared to shadow cones with linear profiles at input fluences higher than 10 J/cm².

Laser processing is useful for topographical and band structure modification of semiconductors. We used a Scanning Tunneling Microscope (STM) to map topography and spectra around hydrofluoric acid etched silicon (100) damaged with an ultrafast pulsed Yb:KGW laser at 1030nm with duration of 70fs in high vacuum. STM uses an atomically sharp tip and feedback loop controlled piezoelectric crystals to characterize conductive surfaces with atomic resolution. With this, we have observed periodic surface structures. This information can then be used to understand the laser damage process better and eventually can be used to characterize defect formation without the presence of topographical change.

We developed a low reflective beam splitter (BS) for hot-spot monitoring of argon-fluoride (ArF) laser, and detected hot-spot in a laser beam profile only at high discharge current and high output power mode.

Identifying laser induced damage on the surface of optical components for the purpose of tracking its growth over time and repairing it is an important part of the economical operation of the National Ignition Facility (NIF). Optics installed on NIF are monitored in situ for damage growth and can be removed as needed for repair and re-use. An ex-situ automated microscopy system is used to inspect full sized NIF optics allowing for the detection of damage sites <10 μm in diameter. Due to the various morphology of laser damage, several algorithms are used to analyze the microscopy data and identify damage regardless of size, while ignoring features not related to laser damage. This system has significantly increased the lifetime of NIF final optics (≈2.3x) thereby extending beyond the capabilities of the in-situ inspection by itself.

Subwavelength, low-haze, anti-reflective (AR) nano-textured surfaces are an effective replacement for thin-film AR coatings (TFARCs) with the potential to increase reliability and minimize thermo-optic effects in kW-class diamond-based laser systems. Etched directly into optical surfaces, AR nano-textured surfaces can yield high optical damage resistance combined with high transmission, low back reflection, and low absorption values equivalent to the bulk substrate material. In this initial study, Random AR (RAR) nano-structures were etched into monocrystalline chemical vapor deposited (CVD) diamond windows. Photothermal common-path interferometry (PCI) measurements at 1064nm were conducted in order to characterize the level of absorption at the surfaces and through the bulk of diamond substrates. Nano-second pulsed laser induced damage threshold (LiDT) measurements at 1064nm were conducted, and damage sites were analyzed via scanning electron microscopy (SEM) to understand damage mechanisms in both as-polished and RAR nano-textured diamond samples.

Recent work utilizing metal etching masks to fabricate substrate-engraved metasurfaces have been handicapped by the available etching depth, restricting the bandwidth of antireflective performance. Advances made to etch mask technology to facilitate deeper etching will be discussed here, and the taller ensuant metasurface features will be presented. The antireflective performance of these high aspect ratio structures (broad acceptance angles and broadband antireflective performance for both polarizations) will be discussed.

Laser-induced contamination (LIC) degrades the performance of optical components and can result in optical losses or even laser-induced damage. LIC deposit formation limits reliable operation of high repetition rate industrial lasers. In this work, we investigate LIC growth on dielectric oxide thin films in air environment irradiated by MHz sub-ps laser at 515 nm. We study the LIC growth dynamic in dependence on thin film deposition method, thin film material and thin film thickness.

The pulsed laser induced damage threshold (LiDT) of Random Anti-Reflective (RAR) nano-textured fused silica optics has been shown to be many times higher than thin-film AR coated optics at wavelengths ranging from the near UV through the NIR. Because an RAR nano-texture is formed by a plasma etch process that removes part of the optic surface, the observed increase in damage resistance has kept track with the LiDT advances attained by low roughness super-polishing and damage pre-cursor mitigation techniques. In this work, nano-second pulse LiDT testing of RAR nano-textured optics was conducted at the deep UV wavelength of 266nm. The effect on 266nm LiDT of the uniform removal of additional surface material from fused silica optics using a dry plasma etch process was investigated. This plasma-polishing (PP), pre-RAR process was varied using fluorine-based chemistries that removed 100-300nm of material from each test surface, with surface roughness then characterized using white-light interferometry. Photothermal interferometry confirmed that no surface absorption was added by the PP, RAR, and PP-RAR plasma etching. Both standard grade, and ultra-low bulk absorption (low-OH) fused silica were included in the tests. RAR nanotextured surfaces showed an average damage threshold of 8.4 J/cm², a level 3 times higher than a commercially available thin-film AR coated surface. Unexpected from pulsed LiDT testing at many longer wavelengths, all plasma etched surfaces exhibited less than half the damage threshold of the untreated, as-polished fused silica surfaces, and there was no observed correlation with surface roughness or plasma etch depth. From work by others it was theorized that exposure to the deep UV photons generated by the plasma might induce absorptive electronic defects in the fused silica material that could explain the reduced damage resistance relative to non-exposed surfaces. As an initial test of this concept an RAR nano-textured sample was baked at 400C to remove the suspected electronic defect. The subsequent pulsed LiDT of this one annealed sample was found to be 15.5 J/cm², nearly double that of all other plasma etched samples. Further work to confirm this result is on-going.

Laser-induced contamination (LIC) can be a major concern of using UV laser systems. Surface contamination occurs via interactions between the UV laser and particulates, water vapor condensate, organics, and airborne molecular contaminates (AMC) from the environment or outgassing from system materials. A brief review of contamination of optics will lead into present results from long-term 355 nm quasi-CW laser transmission experiments at Edmund Optics. Time lapse microscopy was used to monitor nucleation and growth of surface contaminants. Laser burn boxes were constructed for use as a controlled UV LIC testbed; experimental results are presented on transmission losses for various material preparation methods.

We outline the development of a high-power-handling deformable mirror device, based on a modified Thorlabs DMH40, employing a low-loss substrate-transferred crystalline coating as the reflective element. In standard products, this system features a metal coated (Ag or Al) 18 mm diameter × 150 μm thick BK10 glass substrate mounted to a 40-segment piezoelectric actuator, enabling Zernike compensation up to 4th order, with a peak-to-valley stroke up to ±17.6 μm. In the modified variant described here, the metal coating is replaced with a high-reflectivity (~99.998%) and low-stress (compressive, ~130 MPa) monocrystalline GaAs/AlGaAs Bragg stack transferred to the thin glass substrate via direct bonding. While maintaining similar physical performance, this custom system exhibits a substantial enhancement in power handling, with laser-induced damage tests (performed by Spica Technologies, Inc.) yielding a continuous-wave damage threshold of 75 MW/cm² at 1070 nm with a 1/e2 spot diameter of 32.8 μm.

Exit surface damage on high value fused silica final optics on the NIF is sometimes too large to be mitigated with the currently used technique of removing the damage by CO2 laser machining a cone into the surface. To extend the service life of the optic, a 2 cm diameter shadow is created at the damage using a programmable spatial light modulator at the front end of the laser system. The use of this shadow technique is limited by the obscuration due to the large size of the shadow. An alternative approach is to create the shadow by machining a cone on the input surface opposite the damage. This reduces the shadow a rea, and thus the obscuration by several orders of magnitude. Additional benefits in service life of optics would be realized if the shadow cone size could be increased from current 600 m diameter. There are fabrication challenges encountered when the cone size is increased. To overcome this problem, the shadow performance of a hexagonal array of four 600 m diameter cones has been tested. We report on shadow leakage, bulk damage, and exit surface intensification issues presented by this array and techniques to address those issues.

We demonstrate a novel concept for an all-optical switch based on the optical Kerr-effect in thin film interference coatings. The switching between transmittance and reflectance relies on highly Kerr-active coating materials in combination with large internal intensity enhancement in thin film interference coatings. The paper investigates the switching performance as well as its relation to the laser induced damage threshold of these novel components. A modulation depth of 30 % was achieved without damage to the component, which very promising for later applications as power limiters or mode locking components.

Crystalline sesquioxide films (Sc₂O₃, Y₂O₃, Lu₂O₃) produced by pulsed-laser deposition were examined for laser damage resistance with pulses of 500 fs duration, at a wavelength of 1030 nm and at a 10 Hz repetition rate. Comparable tests were performed with amorphous magnetron-sputtered thin films (SiO₂, HfO₂, Nb₂O₅). We found the laser-induced damage thresholds of the sesquioxides are close to those of HfO₂ in the multi-pulse test regime. The results are the basis for designs of damage resistant re ective components used in ultrashort-pulse lasers.

Latest advances of high intensity laser facilities enable the beam transport of petawatt laser pulses and can provide novel fundamental insights in high energy plasma physics or laser fusion. The very high peak intensities put enormous demands on the required large sized optics. Beam transport mirrors reflect pulses with only several tens of fs and maintain their phase while providing best possible laser induced damage threshold. State of the art, such mirrors are mostly manufactured by thermal evaporation techniques as they provide a large and uniform deposition area. Their porous layer structure causes changing spectral characteristics and wavefront when vacuum-air cycled. Especially large sized mirrors can show crazing and thereby decrease up-time of PW beamlines. In contrast, sputtered layers are very compact and provide non changing characteristics. Stable and reproducible sputter processes enable the deposition of more complex design structures necessary for further optimization of the laser induced damage threshold. However, deposition rate is slow and an uniform large sized area difficult to achieve for sputtered coatings. In our study, we show a self-constructed and built-up ion beam sputtering (IBS) machine capable to deposit large sized substrates up to a diameter of 550 mm. A design study is presented to evaluate best HR810nm mirror to meet demanding spectral requirements and providing maximized laser damage threshold for HAPLS at ELI beamlines. In the end, a field optimized design is applied with a measured LIDT of 0.9 J/cm² at 42 fs and 1 kHz. This design is used to manufacture beam transport mirrors for HAPLS applying IBS.

The increase of continuous wave laser power is an important topic in various industrial and defense applications. One of the important limitation is due to optical coatings. In order to study this absorption, it is of prime importance to measure and determine the origin of this absorption. We have developed a LIT system (LIT) to perform low-absorption measurement at 1.07 μm. A multipass setup was realized and calibrated with a sensitivity of a few ppm and a ten times better accuracy is demonstrated. Then, this instrument was used to study single layers made with different materials and deposited by PIAD and multilayer components.

Absorptance is often considered a static feature of an optical element that is determined via standardized measurement procedures. Although such measurements are often performed using optical instruments with low light intensity, in high power laser applications irradiation conditions are considerably different. Optics might become unstable due to highly intense light: optical properties change in a nonlinear way and might eventually lead to laser-induced damage. To study these effects we employed the common-path interferometry technique in combination with a high energy and high average power laser source, operating at 1 MHz repetition rate and delivering 10 ps pulses at 355 nm wavelength. We investigated an anti-reflective (AR@355 nm) coating deposited using ion beam sputtering on a lithium triborate (LBO) crystal. Our preliminary results indicate both strong nonlinear absorptance and fatigue near the damaging fluence, however, damage events were not directly related to the critical absorptance level. An attempt is made to predict the lifetime of an AR coated optics by establishing a numerical model of nonlinear absorption.

Subsurface damage (SSD) in optical components is almost unavoidably caused by mechanical forces involved during grinding and polishing and can be a limiting factor, particularly for applications that require high laser powers. In this contribution, non-destructive characterization techniques are evaluated with respect to their capability to determine SSD in fused silica. For this, differently polished surfaces with different SSD levels have been prepared. An initial destructive analysis using etching in hydrofluoric acid in combination with white light interferometry revealed a high amount of SSD in one of the sample types compared to a very low amount of SSD in a second one. It is shown that nondestructive absorption as well as scattering measurements are sensitive towards SSD related differences in the samples. Finally, laser-induced damage tests proved a significant impact of SSD on the laser stability by determining a reduced damage threshold of 31 ± 3 J/cm² for the sample with high amount of SSD compared to 45 ± 5 J/cm² for the high-quality polished sample.

This article is focused on the design of a beam delivery system based on hollow-core photonic crystal fiber. For our experiment, we chose a fiber with the Kagome structure developed by GLOphotonics. The central wavelength of the delivered beam was 1030 nm, so we chose the fiber PMC-C-Yb-7C. The first part of the article is a brief introduction to PERLA 100, the laser used for testing the efficiency of the beam delivery system developed by HiLASE Centre. The reader will be acquainted with the laser system parameters. The input beam parameters play an important role in the efficiency of focusing into the fiber. One of the key parameters is the M2 of the beam, as it has a direct effect on the size of the waist at the point of entry into the fiber. Another important parameter is the maximum energy in one pulse which can destroy the fiber structure. The size of the focusing point must match the size of the MFD of the fiber. Therefore, it is necessary to precisely define the size of the input beam into the focusing assembly with an accuracy of micrometers and to get rid of as many degrees of freedom as possible in the actual setup of the entire system. Another critical parameter is the size of the fiber input angle. The article aims to eliminate as many critical points as possible when setting up a focusing system and thus prevent damage to the fiber structure. One of the points is the simulation and calculation of the maximum possible loading of the fiber microstructure before its damage. With the help of gradual design modification, the aim is to achieve a coupling efficiency of more than 90 % by scaling the PERLA 100 output power from units of W up to 100 W.

The Dragonfly Mass Spectrometer (DraMS) being developed at NASA’s Goddard Space Flight Center will use a solidstate 266-nm pulsed Nd:YAG laser to perform compositional analysis on the surface of Titan. Due to the high fluence of the focused pulse energy on the laser’s beam steering unit (BSU) and the mass spectrometer window, the damage threshold of these optics in a Titan atmosphere needed to be characterized. This paper details the test setup and the successful demonstration of testing the highest fluence optics for the expected mission duration of 2 million laser pulses in a Titanrelevant atmosphere.

The removal of multi-compound protective thin PVD films for stressed industrial tools using laser ablation could enhance or replace currently used procedures. Developing a laser removal process can shorten the processing time and costs. In the first step, the laser-induced damage threshold of the thin CrAlSiN coating and the WC-Co material was measured. Nanosecond and picosecond laser pulses were used for comparison. Furthermore, the dependence of the ablated material volume and ablation depth on the fluence and the number of pulses was measured. Finally, spectral analysis of the laser plasma generated during ablation was performed.

Optical elements are the main parts in laser system, which limit the total generated output power due to optical resistivity. The increase of beam diameter dimensions may compensate the optical performance of elements, however it leads to the increase of laser system size. Thus, any improvement in optical coatings has impact on either higher output power or lowering the size of system itself. Glancing angle deposition method is presented to produce porous nanostructured coatings, which are characterized by low inner stress. Multilayer Bragg mirrors are formed using only silica material to achieve high laser-induced damage threshold value. Laser conditioning effect is applied, to improve optical performance in ns regime and reach LIDT values over 180 J/cm².

The rapid deployment of high-energy laser systems has significantly pushed the practical limit of laser-induced optics damage. Most systems have chosen to scale the aperture of the laser system to operate within the damage limitations. However, most damage testing protocols do not take into consideration the sampling area of the damage testing beam with respect to the size of the extraction aperture. In this work, we review examples of laser systems where damage testing with small-scale S-on-1 results failed to predict the damage subsequently observed on a full aperture system. We provide guidance on how to adjust the post-coating damage testing protocol to gain confidence that the full-aperture optic will not be damaged during nominal high-fluence operations.