The damage characteristics of fused silica were investigated under low-temporal coherence light (LTCL). It was found that the laser-induced damage threshold (LIDT) of fused silica for the LTCL was lower than that of the single longitudinal mode pulse laser, and for the LTCLs, the LIDTs decrease with the increasing of laser bandwidth, which is not consistent with the temporal spike intensity. This is due to the nonlinear self-focusing effect and multi-pulse accumulation effect. The specific reasons were analyzed based on theoretical simulation and experimental study. This research work is helpful and of great significance for the construction of high-power LTCL devices.

Plasma-enhanced atomic layer deposition (PEALD) is gaining interest in thin films for laser applications, and post-annealing treatments are often used to improve thin film properties. However, research to improve thin film properties is often based on an expensive and time-consuming trial-and-error process. In this study, PEALD-HfO2 thin film samples were deposited and treated under different annealing atmospheres and temperatures. The samples were characterized in terms of their refractive indices, layer thicknesses and O/Hf ratios. The collected data were split into training and validation sets and fed to multiple back-propagation neural networks with different hidden layers to determine the best way to construct the process–performance relationship. The results showed that the three-hidden-layer back-propagation neural network (THL-BPNN) achieved stable and accurate fitting. For the refractive index, layer thickness and O/Hf ratio, the THL-BPNN model achieved accuracy values of 0.99, 0.94 and 0.94, respectively, on the training set and 0.99, 0.91 and 0.90, respectively, on the validation set. The THL-BPNN model was further used to predict the laser-induced damage threshold of PEALD-HfO2 thin films and the properties of the PEALD-SiO2 thin films, both showing high accuracy. This study not only provides quantitative guidance for the improvement of thin film properties but also proposes a general model that can be applied to predict the properties of different types of laser thin films, saving experimental costs for process optimization.

With ultrafast laser systems reaching presently 10 PW peak power or operating at high repetition rates, research towards ensuring the long-term, trouble-free performance of all laser-exposed optical components is critical. Our work is focused on providing insight into the optical material behavior at fluences below the standardized laser-induced damage threshold (LIDT) value by implementing a simultaneous dual analysis of surface emitted particles using a Langmuir probe (LP) and the target current (TC). ${\mathrm{HfO}}_2$ and ${\mathrm{ZrO}}_2$ thin films deposited on fused silica substrates by pulsed laser deposition at various ${\mathrm{O}}_2$ pressures for defect and stoichiometry control were irradiated by Gaussian, ultrashort laser pulses (800 nm, 10 Hz, 70 fs) in a wide range of fluences. Both TC and LP collected signals were in good agreement with the existing theoretical description of laser–matter interaction at an ultrashort time scale. Our approach for an in situ LIDT monitoring system provides measurable signals for below-threshold irradiation conditions that indicate the endurance limit of the optical surfaces in the single-shot energy scanning mode. The LIDT value extracted from the LP-TC system is in line with the multipulse statistical analysis done with ISO 21254-2:2011(E). The implementation of the LP and TC as on-shot diagnostic tools for optical components will have a significant impact on the reliability of next-generation ultrafast and high-power laser systems.

Multilayer dielectric gratings (MLDGs) are crucial for pulse compression in picosecond–petawatt laser systems. Bulged nodular defects, embedded in coating stacks during multilayer deposition, influence the lithographic process and performance of the final MLDG products. In this study, the integration of nanosecond laser conditioning (NLC) into different manufacturing stages of MLDGs was proposed for the first time on multilayer dielectric films (MLDFs) and final grating products to improve laser-induced damage performance. The results suggest that the remaining nodular ejection pits introduced by the two protocols exhibit a high nanosecond laser damage resistance, which remains stable when the irradiated laser fluence is more than twice the nanosecond-laser-induced damage threshold (nanosecond-LIDT) of the unconditioned MLDGs. Furthermore, the picosecond-LIDT of the nodular ejection pit conditioned on the MLDFs was approximately 40% higher than that of the nodular defects, and the loss of the grating structure surrounding the nodular defects was avoided. Therefore, NLC is an effective strategy for improving the laser damage resistance of MLDGs.

The laser-induced damage threshold (LIDT) of plate laser beam splitter (PLBS) coatings is closely related to the subsurface absorption defects of the substrate. Herein, a two-step deposition temperature method is proposed to understand the effect of substrate subsurface impurity defects on the LIDT of PLBS coatings. Firstly, BK7 substrates are heat-treated at three different temperatures. The surface morphology and subsurface impurity defect distribution of the substrate before and after the heat treatment are compared. Then, a PLBS coating consisting of alternating HfO2–Al2O3 mixture and SiO2 layers is designed to achieve a beam-splitting ratio (transmittance to reflectance, s-polarized light) of approximately 50:50 at 1053 nm and an angle of incidence of 45°, and it is prepared under four different deposition processes. The experimental and simulation results show that the subsurface impurity defects of the substrate migrate to the surface and accumulate on the surface during the heat treatment, and become absorption defect sources or nodule defect seeds in the coating, reducing the LIDT of the coating. The higher the heat treatment temperature, the more evident the migration and accumulation of impurity defects. A lower deposition temperature (at which the coating can be fully oxidized) helps to improve the LIDT of the PLBS coating. When the deposition temperature is 140°C, the LIDT (s-polarized light, wavelength: 1064 nm, pulse width: 9 ns, incident angle: 45°) of the PLBS coating is 26.2 J/cm2, which is approximately 6.7 times that of the PLBS coating deposited at 200°C. We believe that the investigation into the laser damage mechanism of PLBS coatings will help to improve the LIDT of coatings with partial or high transmittance at laser wavelengths.

Various coatings in high-power laser facilities suffer from laser damage due to nodule defects. We propose a nodule dome removal (NDR) strategy to eliminate unwanted localized electric-field (E-field) enhancement caused by nodule defects, thereby improving the laser-induced damage threshold (LIDT) of laser coatings. It is theoretically demonstrated that the proposed NDR strategy can reduce the localized E-field enhancement of nodules in mirror coatings, polarizer coatings and beam splitter coatings. An ultraviolet (UV) mirror coating is experimentally demonstrated using the NDR strategy. The LIDT is improved to about 1.9 and 2.2 times for the UV mirror coating without artificial nodules and the UV mirror coating with artificial nodule seeds with a diameter of 1000 nm, respectively. The NDR strategy, applicable to coatings prepared by different deposition methods, improves the LIDT of laser coating without affecting other properties, such as the spectrum, stress and surface roughness, indicating its broad applicability in high-LIDT laser coatings.

In this paper, the feasibility of a high laser damage threshold liquid crystal spatial light modulator based on gallium nitride (GaN) transparent conductive electrodes is proved. The laser-induced damage threshold (LIDT) is measured, and a high LIDT reflective optically addressed liquid crystal light valve (OALCLV) based on GaN is designed and fabricated. The proper work mode of the OALCLV is determined; the OALCLV obtained a maximum reflectivity of about 55% and an on–off ratio of 55:1, and an image response is demonstrated.

Single-shot laser-induced damage threshold (LIDT) measurements of multi-type free-standing ultrathin foils were performed in a vacuum environment for 800 nm laser pulses with durations τ ranging from 50 fs to 200 ps. The results show that the laser damage threshold fluences (DTFs) of the ultrathin foils are significantly lower than those of corresponding bulk materials. Wide band gap dielectric targets such as SiN and formvar have larger DTFs than semiconductive and conductive targets by 1–3 orders of magnitude depending on the pulse duration. The damage mechanisms for different types of targets are studied. Based on the measurement, the constrain of the LIDTs on the laser contrast is discussed.

Stimulated Brillouin scattering (SBS) and the laser-induced damage threshold (LIDT) in different multimode glass fibers with a core diameter of 200 μm are determined. Antireflective coatings for fiber end-faces with high LIDT are developed, which enhance the SBS reflectivity and reduce unwanted front-face reflections. The morphology of pump- and Stokes-radiation induced damages is investigated using atomic force microscopy.