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Sol–gel nano‐silica antireflective (AR) coatings with moisture resistance are widely used for optical elements, such as potassium dihydrogen phosphate (KDP) crystals, but their mildew resistance is often disregarded. This work reports a double‐layer AR coating with moisture resistance and mildew resistance for KDP crystals. A polydimethylsiloxane‐modified dense silica coating and a quaternary ammonium salt (QAS) modified nanoporous silica coating are selected as the bottom layer and top layer, which effectively serve as a moisture barrier and an antireflection layer, respectively. The coated KDP crystal shows excellent antireflection properties with a maximum transmittance of 99.1% at 532 nm. Perfluorooctyltriethoxysilane vapor treatment is performed further to improve the resistance to moisture and mildew. The resultant double‐layer coating exhibits superior moisture resistance with almost no change in optical transmittance after a 3‐month exposure to a high‐humidity environment. The introduction of QAS and hydrophobicity in the top layer provides exceptional resistance against mildew, achieving an antimicrobial rate of 99.9% against E. coli and A. flavus. Moreover, the laser‐induced damage threshold reaches 17.0 J cm−2 (355 nm, 4.5 ns). This work imparts moisture resistance and mildew resistance to AR coatings, providing valuable insights for designing multifunctional AR coatings on optical components. [ABSTRACT FROM AUTHOR]

When irradiated by high-power lasers, fused silica optical component can be ablated, which seriously affects their laser-conducing capability and service life. Numerical simulations have been applied to investigate the ablation process, laser-induced damage threshold (LIDT), and propagation loss of fused silica optical component. The depth of the ablation crater increases linearly with the duration of irradiation, while the rate of development in the width of the ablation crater gradually decreases. The LIDT of the front surface of the fused silica optical component will significantly decrease, while the propagation loss of the fused silica component will have a considerable increase when the front surface of fused silica is damaged under laser irradiation. The propagation loss and the LIDT of the fused silica’s front surface are 26.49, 21.19, 20.60, 16.83, and 16.41GW/cm2 and 0.41, 1.02, 2.24, 3.46, and 5.31dB, respectively, after 50, 100, 150, 200, and 250μs of ablation. This work provides novel opportunities for investigating the intrinsic mechanism of laser-induced damage to fused silica, and offers guidance for the future development of fused silica optical elements that are highly resistant to laser-induced damage. [ABSTRACT FROM AUTHOR]

This work is devoted to the development of a compact source of coherent radiation with frequency-energy characteristics and a spectral generation range that allows remote determination of background concentrations of greenhouse gases in the atmosphere. The aim of this work was to create a frequency parametric converter based on ZGP, pumped by Ho:YAG laser radiation. For use as a source in a mobile lidar for remote determination of the concentration of greenhouse gases in the atmosphere. In the course of the research, a layout of an Optical parametric oscillator OPO based on a ZGP crystal with Ho:YAG laser radiation pumping was developed. The system's continuous failure-free operation time was 1.5 h at a pulse repetition rate of 10 kHz and a pulse energy of the generated radiation of 0.08 mJ. The tuning range of the OPO was from 3.3 to 5 μιτι when using a Lyot filter. The losses from the average generation power when the Lyot filter was introduced into the resonator were 30%. At the same time, it was possible to achieve a linewidth of the generated radiation of 0.7 nm. The divergence of the generated radiation did not exceed 1.5 mrad.The absorption spectrum of gases CO2, CH4, N2O, CO in a gas cell was simulated for the entire generation range of the ZnGeP2-based OPO. As a result of the simulation, the most intense absorption lines of gases CO2, CH4, N2O, CO in the OPO tuning range were revealed, the central wavelengths of the absorption lines and their spectral width were determined. [ABSTRACT FROM AUTHOR]

Featured Application: Large scale laser operation. Complex laser use. The maximum energy at which a laser can be operated safely is a matter of paramount importance. This is patently related to laser induced damage. In the nanosecond regime, this poses a unique challenge, as it is not solely influenced by laser intensity or thermal load. Instead, it arises from the cumulative effects that includes those two factors. While extensive research has explored this dependence for various pulse lengths, the exploration of different longitudinal modes and temporal shapes is relatively limited. Our study aims to fill this gap by determining the safe operational fluence for any pulse shape, leveraging established dependencies on pulse duration. We propose a straightforward and adaptable method to ascertain these operational limits, independent of the type or origin of laser damage. This approach allows us to derive fluence limits for diverse pulse shapes. [ABSTRACT FROM AUTHOR]

Mid‐infrared (MIR) pulsed lasers operating at 2–5 µm have important applications in communication, sensing, and medicine. However, the lack of robust MIR saturable absorbers (SAs) remains a major obstacle. Here, a semiconductor material cadmium oxide (CdO) film with high laser‐induced damage threshold (800 nm, 134 mJ cm−2) and broadband saturable absorption (2.0–3.9 µm) is investigated. The effective tuning of the nonlinear optical response of CdO is demonstrated by adjusting the carrier concentration via a tungsten (W)‐doping scheme. The saturable absorption is improved and carrier relaxation process is accelerated after increasing the W‐dopant level. Based on these findings, the robust CdO‐SAs with customizable parameters are realized and Q‐switched lasers with decreasing pulse width from 372 to 254.3 ns are obtained at 2 µm. The design flexibility provided by CdO opens up a large parameter space that enables the continuous improvement of compact and high‐performance MIR ultrafast lasers. [ABSTRACT FROM AUTHOR]

Micro surface defects (SDs) would be unavoidably induced on most fused silica surfaces (FSSs), substantially reducing their laser-induced damage thresholds (LIDTs). There is still no clear understanding of the relation between SD structural feature and their LIDTs, which poses a challenge to the recognition and mitigation of the dangerous SDs with low LIDTs in industrial production. In this work, the brittle-plasticity and stress states of the SDs are found to dominate the atomic point-defect densities on FSSs and resultantly dominate their LIDTs for the first time. Based on this, the SDs have been divided into four categories: pressure-induced brittle defects (PBDs), pressure-induced plastic defects (PPDs), tension-induced brittle defects (TBDs) and tension-induced plastic defects (TPDs). Based on the tested LIDTs, laser damage morphologies and photoluminescence (PL) characteristics, the laser damage resistance of different kinds of SDs are compared, whose reasons are revealed on the basis of the molecular dynamics (MD) simulations. The sharp increase of the atomic point-defect density from the plasticity to the brittleness of the material, the significant disparity in tensile and compressive strength of fused silica, the distinctly different material response behaviours under tensile and compressive forces, as well as the opposite effects of the tensile and compressive forces on the material compactness significantly affect the atomic point-defect densities on FSSs and resultantly contribute to the different laser damage resistance of different kinds of SDs. This work possesses great significance in solving the laser damage on FSSs. It could also provide a new understanding of the impact of the tensile and compressive forces on the LIDTs of various optical elements. [ABSTRACT FROM AUTHOR]

This work is devoted to the development of a compact source of coherent radiation with frequency-energy characteristics and a spectral generation range that allows remote determination of background concentrations of greenhouse gases in the atmosphere. The aim of this work was to create a frequency parametric converter based on ZGP, pumped by Ho:YAG laser radiation. For use as a source in a mobile lidar for remote determination of the concentration of greenhouse gases in the atmosphere. In the course of the research, a layout of an Optical parametric oscillator OPO based on a ZGP crystal with Ho:YAG laser radiation pumping was developed. The system’s continuous failure-free operation time was 1.5 h at a pulse repetition rate of 10 kHz and a pulse energy of the generated radiation of 0.08 mJ. The tuning range of the OPO was from 3.3 to 5 μm when using a Lyot filter. The losses from the average generation power when the Lyot filter was introduced into the resonator were 30%. At the same time, it was possible to achieve a linewidth of the generated radiation of 0.7 nm. The divergence of the generated radiation did not exceed 1.5 mrad.The absorption spectrum of gases CO2, CH4, N2O, CO in a gas cell was simulated for the entire generation range of the ZnGeP2-based OPO. As a result of the simulation, the most intense absorption lines of gases CO2, CH4, N2O, CO in the OPO tuning range were revealed, the central wavelengths of the absorption lines and their spectral width were determined.

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.

The nonlinear properties of zinc germanium diphosphide (ZGP) crystals enable their applications in powerful mid-IR optical parametric oscillators and second-harmonic generators. This paper summarizes the mechanisms of the laser-induced damage (LID) of high-purity ZGP crystals under periodically pulsed nanosecond irradiation by a Ho3+:YAG laser at 2.1 μm. The ZGP samples were manufactured by "LOC" Ent., Tomsk, Russia, or the Harbin Institute of Technology, China. The impact of processing techniques and the post-growing methods for polishing and anti-reflective coatings on the LID threshold are discussed. The importance of the defect structure of the crystal lattice and the parameters of transparent coatings for increasing the LID threshold are also discussed. The impact of the test laser parameters on the LID threshold and the transient area near the LID threshold obtained using digital holography are analyzed. The influence of the pre-damage processes on the optical parametric oscillations is reported. Lastly, the prospects for improving ZGP crystals to further increase the LID threshold are discussed. [ABSTRACT FROM AUTHOR]

The maximum energy at which a laser can be operated safely is a matter of paramount importance. This is patently related to laser induced damage. In the nanosecond regime, this poses a unique challenge, as it is not solely influenced by laser intensity or thermal load. Instead, it arises from the cumulative effects that includes those two factors. While extensive research has explored this dependence for various pulse lengths, the exploration of different longitudinal modes and temporal shapes is relatively limited. Our study aims to fill this gap by determining the safe operational fluence for any pulse shape, leveraging established dependencies on pulse duration. We propose a straightforward and adaptable method to ascertain these operational limits, independent of the type or origin of laser damage. This approach allows us to derive fluence limits for diverse pulse shapes.

Laser-based light sources have fostered innovative developments in biomedical and biosensor fields. However, laser-induced damage to optical components is a limitation for designing and implementing highly sensitive biosensors, necessitating the development and characterization of suitable optical components. Microscope glass slides are among the most extensively used optical units in this field. This study investigated the laser-induced damage threshold (LIDT) of high-quality microscope glass slides obtained from three different vendors. An S-on-1 protocol following the ISO 21254 series standards was adopted to ensure a meaningful comparative analysis. Multiple laser pulses at a constant fluence (at the three laser wavelengths most widely used in biosensors) were used for LIDT tests. An automated test bench was developed and employed to minimize the influence of human factors on the test results. The fatigue damage mechanism was observed in all the samples. The findings revealed good consistency among LIDT values within and across batches from the same vendor. However, a notable discrepancy was observed when comparing the results of slides obtained from different vendors, with threshold values differing by up to two-fold. This study emphasizes the need to carefully consider the glass material source when selecting microscope glass slides for laser-sensitive applications. [ABSTRACT FROM AUTHOR]

Hafnium oxide thin films have attracted great attention as promising materials for applications in the field of optical thin films and microelectronic devices. In this paper, hafnium oxide thin films were prepared via DC magnetron sputtering deposition on a quartz substrate. The influence of various negative biases on the structure, morphology, and mechanical and optical properties of the obtained films were also evaluated. XRD results indicated that ( 1 ¯ 11 )-oriented thin films with a monoclinic phase could be obtained under the non-bias applied conditions. Increasing the negative bias could refine the grain size and inhibit the grain preferred orientation of the thin films. Moreover, the surface quality and mechanical and optical properties of the films could be improved significantly along with the increase in the negative bias and then deteriorated as the negative bias voltage arrived at −50 V. It is evident that the negative bias is an effective modulation means to modify the microstructural, mechanical, and optical properties of the films. [ABSTRACT FROM AUTHOR]

Low‐dimensional lead‐halide perovskites show wide structural and compositional diversity. Multiple functionalities can be introduced in these materials for diverse linear and nonlinear optical applications. Nonlinear optical (NLO) processes depend on material polarizability, crystal symmetry, and processibility. The flexibility of choosing organic cations in lead‐halide perovskites provides an opportunity for enhanced NLO responses by enhancing the overall system polarizability. A highly polarizable diisopropylammonium [Dipa; ((CH3)2CH)2NH2+] is used as an A‐site cation to synthesize one‐dimensional (1D) lead‐iodide (DipaPbI3) perovskite single crystals and the third‐harmonic generation (THG) in the excitation wavelength range of 1200–1600 nm is explored. DipaPbI3 single crystals exhibit exceptionally efficient resonance‐enhanced THG, amazing optical stability, and a high polarization ratio due to enhanced bulk‐polarization. The THG efficiency (χ(3) ≈ 4 × 10−18 m2 V−2) and laser‐induced damage threshold (LIDT, 144 GW cm−2) are an order of magnitude higher than the reported perovskites explored as THG materials. Density functional theory calculations show a significantly higher polarizability for Dipa cation, asserting the influence of the cation polarizability on the NLO efficiency of the perovskite. The stability of these single crystals in ambient conditions for an extended period adds to their potential for commercial application in the near future. [ABSTRACT FROM AUTHOR]

In this article, the optical and structural evaluation of a bulk metal mirror as a back mirror of a flashlamp-pumped Nd:YAG laser system has been presented. The XRD and SEM accompanied by EDX analysis showed that the metal mirror can be considered as a substrate of aluminum with a micrometer coating of nickel composite. The results of reflectance spectrum measurement and laser performance of a free pulsed Nd:YAG system showed that, in comparison with aluminum and dielectric mirrors, the nickel mirror has a lower reflectance at 1064 nm. Although, it has a higher lasing threshold and lower slope efficiency but comparable amounts to those of aluminum and dielectric mirrors. The laser-induced damage threshold measured for the nickel mirror was 4.8 J/cm2 which is high enough for high-energy laser applications. [ABSTRACT FROM AUTHOR]

In laser application systems, the optical film is one of the most important parts of the system, as well as its weakest link. Its damage performance determines the output characteristics and safety performance of the laser system. This paper focuses on the fundamental frequency reflection of dielectric films used in large high-powered laser devices. The study of the dielectric film's initial laser damage performance and laser damage growth performance is carried out through laser damage testing and microscopic morphology testing of the damage. The results show two different damage morphologies: type 1 damage (film discoloration damage) and type 2 damage (cratered damage), and the damage growth behavior between the two is very different, with type 1 damage not growing and type 2 damage growing rapidly under subsequent episodes that trigger their damage fluxes. The difference in the growth behavior is well explained by the micro-zone surface shape of the damage location. The results of this paper help to deepen the understanding of the dielectric membrane element processing process and the damage growth behavior. [ABSTRACT FROM AUTHOR]

Special pure chalcogenide glass is the material of choice for many mid-infrared optical fibers and fiber lasers. In this paper, the thermo-optical lensing and laser-induced damage were studied in Ge35As10S55 and Ge20As22Se58 glasses and compared with the well-studied As2S3 glass. The thermal Z-scan technique with the quasi-CW Tm-doped fiber laser at 1908 nm was applied to study thermal lensing in chalcogenide glass. The laser-induced damage of various chalcogenide glasses was determined using the one-on-one procedure. The thermal nonlinear refractive index of the Ge35As10S55 and Ge20As22Se58 glasses was found to be lower than that of the As2S3 glass. The laser-induced damage threshold of the Ge20As22Se58 glass was determined to be higher than that of the Ge35As10S55 glass. The difference in the thermal damage threshold of the Ge35As10S55 and Ge20As22Se58 glasses and their lower value in comparison with the As2S3 glass were explained by a deviation from the stoichiometry of glass compositions and their tendency to crystallize. [ABSTRACT FROM AUTHOR]

The effect of doping Mg, Se, and Ca by diffusion into ZnGeP2 on the optical damage threshold at a wavelength of 2.1 μm has been studied. It has been shown that diffusion-doping with Mg and Se leads to an increase in the laser-induced damage threshold (LIDT) of a single crystal (monocrystal), ZnGeP2; upon annealing at a temperature of 750 °C, the damage threshold of samples doped with Mg and Se increases by 31% and 21% from 2.2 ± 0.1 J/cm2 to 2.9 ± 0.1 and 2.7 ± 0.1 J/cm2, respectively. When ZnGeP2 is doped with Ca, the opposite trend is observed. It has been suggested that the changes in the LIDT depending on the introduced impurity by diffusion can be explained by the creation of additional energy dissipation channels due to the processes of radiative and fast non-radiative relaxation through impurity energy levels, which further requires experimental confirmation. [ABSTRACT FROM AUTHOR]

In this study, a novel optical limiting (OL) experimental setup is proposed for evaluating laser-induced damage thresholds (LIDTs) of materials. This technique is based on the pump–probe method, and the damage can be measured using a probe beam with a delay adjusted according to experimental conditions. Moreover, the probe beam is controlled to reach the sample before the pump beam, and the pump beam waist is larger than the probe beam waist to facilitate measurement. In particular, using this probe beam, nonlinear effects of the material can be ignored. Compared with other traditional technologies, the proposed method allows direct observation of the OL threshold of the material as well as measurement of in situ and laser damage of the material. This technique can quantify the in situ damage and LIDTs of materials effectively and conveniently. The validity of this approach is demonstrated by measuring the LIDT of ZnSe. Such measurement method enables searching for more efficient laser protective materials with high LIDTs that can be widely used in laser protection and other applications. [ABSTRACT FROM AUTHOR]

Ambient humidity is an important factor to consider when maintaining dielectric films' component performance. Herein, humidity-influenced experiments were conducted on complex spectral dielectric films based on SiO2 and K9 substrates. Firstly, complex spectral dielectric films' spectral and surface stresses in different humidity environments were measured. Subsequently, laser-induced damage threshold measurements were carried out on these components. The experimental results indicate that the environmental humidity will induce the evolution of the internal structure of the dielectric films on the mirror, resulting in the deformation of the coating surface and a slight shift of the reflection spectrum. At the same time, the environmental humidity also greatly influences the anti-laser damage performance of the dielectric film mirror. Dielectric films based on SiO2 have excellent damage resistance in high-humidity environments. Conversely, K9-based dielectric films have better damage resistance in low-humidity environments. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

The nonlinear properties of zinc germanium diphosphide (ZGP) crystals enable their applications in powerful mid-IR optical parametric oscillators and second-harmonic generators. This paper summarizes the mechanisms of the laser-induced damage (LID) of high-purity ZGP crystals under periodically pulsed nanosecond irradiation by a Ho3+:YAG laser at 2.1 μm. The ZGP samples were manufactured by “LOC” Ent., Tomsk, Russia, or the Harbin Institute of Technology, China. The impact of processing techniques and the post-growing methods for polishing and anti-reflective coatings on the LID threshold are discussed. The importance of the defect structure of the crystal lattice and the parameters of transparent coatings for increasing the LID threshold are also discussed. The impact of the test laser parameters on the LID threshold and the transient area near the LID threshold obtained using digital holography are analyzed. The influence of the pre-damage processes on the optical parametric oscillations is reported. Lastly, the prospects for improving ZGP crystals to further increase the LID threshold are discussed.

The development of high‐power solid‐state lasers is in urgent need of infrared (IR) nonlinear optical (NLO) materials with wide band gaps and high laser‐induced damage thresholds (LIDTs). Herein, a new compressed chalcopyrite‐like IR NLO crystal (Na0.74Ag1.26)BaSnS4 was successfully synthesized using a facile high‐temperature solid‐state method. Its structure can be considered as a variant of chalcopyrite AgGaS2 (AGS)‐type ones. It features a three‐dimensional framework constructed by corner‐sharing {[(Na/Ag)S4]7−}∞ layers and isolated SnS4 tetrahedra with negative cavities occupied by counter ion Ba2+. (Na0.74Ag1.26)BaSnS4 exhibits phase‐matchable moderate SHG response (0.31 × AGS), wide band gap (3.70 eV), and high LIDT (6.44 × AGS). Theoretical calculations reveal that the NLO response of (Na0.74Ag1.26)BaSnS4 is mainly originated from the synergetic effects of AgS4 and SnS4 tetrahedra, and the inclusion of alkaline and alkaline earth metals is responsible for the wide band gap and high LIDT. Moreover, the discovery of this chalcopyrite‐like compound will provide a feasible design strategy for the exploration of new promising IR NLO materials. [ABSTRACT FROM AUTHOR]

Laser‐induced damage on metal parts by stray light is a common issue for high‐energy laser systems, especially inertial‐confinement fusion (ICF) systems. Micro‐dust could be produced from the surface irradiated and adhere to and cause further damage of other optical parts like potassium dihydrogen phosphate (KDP) crystal. We propose a functional gradient film based on aluminum anodization to raise the laser‐induced damage threshold (LIDT). The number of particles produced by a 355‐nm nanosecond laser was considered a factor of LIDT. To investigate the interaction theoretically, a coupled model of electromagnetic radiation and heat conversion based on Ohm's law for a nanosecond laser pulse absorbed by the films was used to calculate the LIDT temperature. Films with different roughnesses and an untreated aluminum alloy (AA) were irradiated. The LIDT was 0.5 J/cm2, with a temperature of 5790 K, which largely prevented the laser damage of the AA and reduced particles produced while metal damaged. The combination of simulations and experiments provided a new and simple indication of LIDT for aluminum‐based functional gradient films. It also provided a guide for clean manufacturing with less particle generation, which is vital to the success of ICF systems that will generate sustainable energy. [ABSTRACT FROM AUTHOR]

With the increasing exploitation of lasers, single-band laser protection has been extensively studied. However, single-band laser protection techniques have remained expensive and failed to meet protection requirements for multi-band lasers. In addition, the actual use of protective films requires a specific transmittance, which is generally not met by regular films. Here, we deposited three non-regularized highly reflective films using SiO2 as the low-refractive-index material and TiO2, HfO2, and Ta2O5 as the high-refractive-index materials by thermal evaporation for achieving multi-band laser protection. To verify the effectiveness of the films, the variation in transmittance, damage threshold, standing-wave electric field, and damage morphology of the films were analyzed at two laser wavelengths, and their protection mechanisms were evaluated based on optical properties and damage resistance. The results showed that the reflectances of the prepared non-regularized films at 1064 nm and 532 nm were greater than 99%, and the laser-induced damage thresholds for TiO2/SiO2, HfO2/SiO2, and Ta2O5/SiO2 films were 5.99, 5.89, and 9.99 J/cm2 at 1064 nm and 3.04 J/cm2, 1.48 J/cm2, and 4.93 J/cm2 at 532 nm, respectively, demonstrating good laser protection. The present work provides a practical and effective solution for multi-band laser protection and the prepared films may be used in numerous laser applications. [ABSTRACT FROM AUTHOR]

A multispectral anti-reflective coating of high radiation strength for laser applications in the IR spectrum for nonlinear ZnGeP2 crystals has been developed for the first time. The coating was constructed using YbF3/ZnS. The developed coating was obtained by a novel approach using ion-beam deposition of these materials on a ZnGeP2 substrate. It has a high LIDT of more than 2 J/cm2. Optimal layer deposition regimes were found for high film density and low absorption, and good adhesion of the coating to the substrate was achieved. At the same time, there was no dissociation of the double compound under high-energy ions. [ABSTRACT FROM AUTHOR]

Hafnium oxide thin films have attracted great attention as promising materials for applications in the field of optical thin films and microelectronic devices. In this paper, hafnium oxide thin films were prepared via DC magnetron sputtering deposition on a quartz substrate. The influence of various negative biases on the structure, morphology, and mechanical and optical properties of the obtained films were also evaluated. XRD results indicated that (1¯11)-oriented thin films with a monoclinic phase could be obtained under the non-bias applied conditions. Increasing the negative bias could refine the grain size and inhibit the grain preferred orientation of the thin films. Moreover, the surface quality and mechanical and optical properties of the films could be improved significantly along with the increase in the negative bias and then deteriorated as the negative bias voltage arrived at −50 V. It is evident that the negative bias is an effective modulation means to modify the microstructural, mechanical, and optical properties of the films.

Laser-based light sources have fostered innovative developments in biomedical and biosensor fields. However, laser-induced damage to optical components is a limitation for designing and implementing highly sensitive biosensors, necessitating the development and characterization of suitable optical components. Microscope glass slides are among the most extensively used optical units in this field. This study investigated the laser-induced damage threshold (LIDT) of high-quality microscope glass slides obtained from three different vendors. An S-on-1 protocol following the ISO 21254 series standards was adopted to ensure a meaningful comparative analysis. Multiple laser pulses at a constant fluence (at the three laser wavelengths most widely used in biosensors) were used for LIDT tests. An automated test bench was developed and employed to minimize the influence of human factors on the test results. The fatigue damage mechanism was observed in all the samples. The findings revealed good consistency among LIDT values within and across batches from the same vendor. However, a notable discrepancy was observed when comparing the results of slides obtained from different vendors, with threshold values differing by up to two-fold. This study emphasizes the need to carefully consider the glass material source when selecting microscope glass slides for laser-sensitive applications.

In order to obtain higher laser-induced damage threshold (LIDT) and lower loss of laser radiation, the incident radiation must have an insignificant absorbance and high anti-reflectance. In this work, a single-layer porous SiO2-based anti-reflective (AR) coating for the optics of Nd:phosphate laser system has been developed on quartz glass optics adopting sol–gel dip coating technique, following quarter wavelength optical design. As measured by spectroscopic ellipsometer, the refractive index (RI) of the coated layer is found to be ~1.2. A maximum transmittance of ~99% in single-layer-coated quartz glass has been achieved at 1054 nm. In addition, the non-quarter wavelength-based double layer with an optical design (glass/ 0.7153 M / 1.134 L / air) and triple-layer AR coating with an optical design (glass / 0.28 H / 1.65 M / 1.03 L / air, where H, M and L indicate one-quarter wave thick layers of high, medium and low RI materials) have been fabricated. The deposition of M and H layers has been made from mixed metal oxide precursor sols of zirconia-silica, while L has been made from silica precursor sol to obtain porous silica coating. A maximum transmittance of about 98.1 and 97.6% was found at 1054 nm in double- and triple-layer AR-coated samples, respectively. The LIDT values have been measured on the AR coatings. Based upon the number of layers in the AR coatings, the LIDT values varied in the range of 8.7–2.4 J cm–2 starting from single to double to triple layer. The AR coatings developed by sol–gel dip coating technique could find application in Nd:phosphate high power laser system. Schematic diagram of single (1LD), Double (2LD) and triple (3LD) layer design AR coated samples; Laser induced damage threshold (LIDT) values of each system mentioned below; Origin plot shows transmittance values of each system. [ABSTRACT FROM AUTHOR]

Polycrystalline zinc selenide (ZnSe) and Cr2+ or Fe2+ doped ZnSe are key optical elements in mid-infrared laser systems. The laser-induced damage of the optical elements is the limiting factor for increasing the power and pulse energy of the lasers. In the present work, the optical damage of the ZnSe, Cr2+:ZnSe, and Fe2+:ZnSe samples induced by a repetitively pulsed Ho3+:YAG laser at 2091 nm was studied. The probability of the optical damage and the laser-induced damage threshold (LIDT) were determined for the samples manufactured using different processing techniques. The highest LIDT was found in ZnSe samples annealed in an argon atmosphere. It was also found that the samples annealed in a zinc atmosphere or with hot isostatic pressing resulted in a decrease in the LIDT. The Cr2+-doped ZnSe had the lowest LIDT at 2.1 µm compared to Fe2+-doped or undoped ZnSe. The LIDT fluence of all tested ZnSe samples decreased with the increase in the pulse repetition rate and the exposure duration. The results obtained may be used to improve the treatment procedures of ZnSe, Cr2+:ZnSe, and Fe2+:ZnSe polycrystals to further increase their LIDT. [ABSTRACT FROM AUTHOR]

Metal chalcogenophosphates are receiving increasing interest, specifically as promising infrared nonlinear optical (NLO) candidates. Here, a rare‐earth chalcogenophosphate Eu2P2S6 crystallizing in the monoclinic noncentrosymmetric space group Pn was synthesized using a high‐temperature solid‐state method. Its structure features isolated [P2S6]4− dimer, and two types of EuS8 bicapped triangular prisms. Eu2P2S6 exhibits a phase‐matchable second‐harmonic generation (SHG) response ≈0.9×AgGaS2@2.1 μm, and high laser‐induced damage threshold of 3.4×AgGaS2, representing the first rare‐earth NLO chalcogenophosphate. The theoretical calculation result suggests that the SHG response is ascribed to the synergetic contribution of [P2S6]4− dimers and EuS8 bicapped triangular prisms. This work provides not only a promising high‐performance infrared NLO material, but also opens the avenue for exploring rare‐earth chalcogenophosphates as potential IR NLO materials. [ABSTRACT FROM AUTHOR]

In this work, the parameters of antireflection interference coatings based on alternating layers of ZnS/Al2O3 on the laser-induced damage threshold (LIDT) of ZGP crystals under the action of Ho:YAG laser radiation at a wavelength of 2.097 μm were determined. The coating deposition was carried out using the ion-beam sputtering method. The LIDT of the sample with a coating based on alternating layers ZnS and Al2O3 was equal to W o E = 3.45 J/cm2, and the LIDT of the uncoated sample was equal to W o E = 2.23 J/cm2. An increase in the optical breakdown threshold by ~55% was observed after the deposition of an AR coating based on ZnS and Al2O3 materials. An assumption was made about the absence of local fluctuations in the composition and mechanical stresses in the case of the coated sample, namely that this leads to good adhesion of the multilayer coating to the polished surface of the crystal, and as a result to an increase in the optical breakdown threshold as compared to the uncoated sample due to closure of the dangling chemical bonds and bulk defects emerging on the polished surface. [ABSTRACT FROM AUTHOR]

Non‐linear optical chalcogenides with a wide band gap (Eg) and excellent NLO properties are key materials for highly desirable multiwaveband tunable optical parametric oscillators (OPOs). We exploit the "electronic structure engineer bucket effect" to develop a novel dual‐waveband SrZnGeS4 with an ultrawide transparency window. It exhibits an asymmetric Fdd2 structure that consists of layers formed by corner‐sharing [ZnGeS6] dimers. SrZnGeS4 is transparent from 0.30 to 23.6 μm, spanning the UV‐, vis‐, mid‐ and far‐IR spectral regions and has the widest Eg (3.63 eV) in the AeMIIMIVQ4 family to date. It exhibits phase matching, high SHG intensities (e.g. 11.0×KDP and 17.5×AGS under λinc=1450 and 950 nm, respectively), and a very high laser‐induced damage threshold (35×AGS). These results not only suggest bright prospects for high‐power laser applications but may also enable applications of the multiwaveband OPO system from the UV‐visible to far‐IR regions. [ABSTRACT FROM AUTHOR]

The high-precision diffraction grating is an important chromatic dispersion component that has been widely used in many fields, including laser beam combining, chirped pulse compression, spectroscopy, among others. In this paper, we review the development status of reflection and transmission gratings with high diffraction efficiency and high laser-induced damage thresholds, such as metal-film and multilayer-dielectric-film gratings. Then, we review the basic principles and most recent stages in the development of manufacturing techniques, such as mechanical scribing, holographic exposure, electron-beam lithography, and nanoimprinting. [ABSTRACT FROM AUTHOR]

• The size of the damage crater in wide-bandgap glass ZBLAN is almost constant. • The selection of the damage crater area has a significant impact on the calculation results of the laser-induced damage threshold. • The laser-induced damage threshold of optical materials can be calculated more accurately through the method of laser direct writing. In this paper, we report a comparative study of the laser damage properties of three different systems for infrared glasses (As 2 S 3 , 70TeO 2 -15ZnO-5La 2 O 3 -10WO 3 (TZLW), and 53ZrF 4 -20BaF 2 -4LaF 3 -3AlF 3 -20NaF (ZBLAN)). The effects of laser pulse power and pulse number on glasses damage crater morphology and damage characteristics were systematically investigated under 800 nm femtosecond laser irradiation. According to the Tauc formula, the bandgap values for As 2 S 3 , TZLW, and ZBLAN glasses are 2.01, 2.70, and 4.98 eV respectively. Under femtosecond laser irradiation, a serious edge collapse is found at the edge of the damage crater for the wide-bandgap ZBLAN glass because the high laser energy density affects the accurate calculation of the laser-induced damage threshold (LIDT). According to the characteristics of ZBLAN, glass damage crater size is not sensitive to the pulse numbers. We proposed employing laser direct writing strip damage and using the linear regression method to accurately calculate the damage threshold. The work provides scientific guidance for accurately obtaining the LIDT of optical glass. [ABSTRACT FROM AUTHOR]

• The damage behavior of two UBCMs with different designs is studied under 7.3-fs pulse irradiation for the first time. • A time-domain electric field model is proposed to explain the origin of the damage and the discrepancy in LIDTs of the two UBCMs. • Incorporating the time-domain electric field model as a merit function contributes to designing high-threshold UBCMs. The laser-induced damage resistance performance of ultra-broadband chirped mirrors (UBCM) is a critical factor influencing the generation of petawatt or exawatt laser pulses in thin film compression techniques. In this study, a few-cycle pulse damage testing platform was set up, and two UBCMs with different designs were fabricated for a comparative study of their laser-induced damage. Because light of varying wavelengths forms an electric field at different times within UBCMs under few-cycle pulse irradiation, a time-domain electric field model was developed to obtain transient electric field variations and explain the damage behavior. The model successfully elucidated the origin of the damage and discrepancy between the two UBCMs in terms of damage thresholds, showcasing its potential applications in designing high-threshold UBCMs for high-power laser systems. [ABSTRACT FROM AUTHOR]

The ZnGeP2 crystal is a material of choice for powerful mid-IR optical parametric oscillators and amplifiers. In this paper, we present the experimental analysis of the optical damage threshold of ZnGeP2 nonlinear crystals induced by a repetitively-pulsed Ho3+:YAG laser at 2091 nm. Two types of ZnGeP2 crystals grown under different conditions were examined using the laser and holographic techniques. The laser-induced damage threshold (LIDT) determined by the pulse fluence or peak intensity was studied as a function of the pulse repetition rate (PRR) and laser exposure duration. The main crystal structure factor for a higher LIDT was found to be a reduced dislocation density of crystal lattice. The ZnGeP2 nonlinear crystals characterized by the high structural perfection with low density of dislocations and free from twinning and stacking faults were measured to have a 3.5 J/cm2 pulse fluence damage threshold and 10.5 MW/cm2 peak intensity damage threshold at 12 kHz PRR; at 40 kHz PRR the pulse fluence damage threshold increased to over 6 J/cm2, but the peak intensity damage threshold dropped to 5.5 MW/cm2. [ABSTRACT FROM AUTHOR]

Abstract In this work, we present our results about the thermal crystallization of ion beam sputtered hafnia on 0001 SiO2 substrates and its effect on the laser-induced damage threshold (LIDT). The crystallization process was studied using in-situ X-ray diffractometry. We determined an activation energy for crystallization of 2.6 ± 0.5 eV. It was found that the growth of the crystallites follows a two-dimensional growth mode. This, in combination with the high activation energy, leads to an apparent layer thickness-dependent crystallization temperature. LIDT measurements @355 nm on thermally treated 3 quarter-wave thick hafnia layers show a decrement of the 0% LIDT for 1 h @773 K treatment. Thermal treatment for 5 h leads to a significant increment of the LIDT values.

In this study, the single- and multiple-pulse laser-induced surface damage characteristics of the Ge 8 As 23 S 69 chalcogenide film under the femtosecond laser irradiation were experimentally investigated. The 1-on-1 and S-on-1 methods were utilized to measure the femtosecond laser damage by using single and multiple pulses, respectively. The femtosecond laser-induced damage threshold (LIDT) was obtained using linear regression method by measuring the damage morphology under different pulse energies and pulse numbers of the femtosecond laser. Results show that the LIDT of the film under single-pulse radiation is higher than that under multiple-pulse radiation because of accumulation and defect effects. For the single-pulse radiation, LIDT is attributed to the field enhancement effect, multiphoton ionization, and avalanche ionization. The single-pulse damage threshold of Ge 8 As 23 S 69 films is 232.548 mJ/cm2. For the multiple-pulse radiation, the LIDT of the film decreases with increasing pulse number due to accumulation and defect effects. [ABSTRACT FROM AUTHOR]

In laser application systems, the optical film is one of the most important parts of the system, as well as its weakest link. Its damage performance determines the output characteristics and safety performance of the laser system. This paper focuses on the fundamental frequency reflection of dielectric films used in large high-powered laser devices. The study of the dielectric film’s initial laser damage performance and laser damage growth performance is carried out through laser damage testing and microscopic morphology testing of the damage. The results show two different damage morphologies: type 1 damage (film discoloration damage) and type 2 damage (cratered damage), and the damage growth behavior between the two is very different, with type 1 damage not growing and type 2 damage growing rapidly under subsequent episodes that trigger their damage fluxes. The difference in the growth behavior is well explained by the micro-zone surface shape of the damage location. The results of this paper help to deepen the understanding of the dielectric membrane element processing process and the damage growth behavior.

The effect of doping Mg, Se, and Ca by diffusion into ZnGeP2 on the optical damage threshold at a wavelength of 2.1 μm has been studied. It has been shown that diffusion-doping with Mg and Se leads to an increase in the laser-induced damage threshold (LIDT) of a single crystal (monocrystal), ZnGeP2; upon annealing at a temperature of 750 °C, the damage threshold of samples doped with Mg and Se increases by 31% and 21% from 2.2 ± 0.1 J/cm2 to 2.9 ± 0.1 and 2.7 ± 0.1 J/cm2, respectively. When ZnGeP2 is doped with Ca, the opposite trend is observed. It has been suggested that the changes in the LIDT depending on the introduced impurity by diffusion can be explained by the creation of additional energy dissipation channels due to the processes of radiative and fast non-radiative relaxation through impurity energy levels, which further requires experimental confirmation.

Special pure chalcogenide glass is the material of choice for many mid-infrared optical fibers and fiber lasers. In this paper, the thermo-optical lensing and laser-induced damage were studied in Ge35As10S55 and Ge20As22Se58 glasses and compared with the well-studied As2S3 glass. The thermal Z-scan technique with the quasi-CW Tm-doped fiber laser at 1908 nm was applied to study thermal lensing in chalcogenide glass. The laser-induced damage of various chalcogenide glasses was determined using the one-on-one procedure. The thermal nonlinear refractive index of the Ge35As10S55 and Ge20As22Se58 glasses was found to be lower than that of the As2S3 glass. The laser-induced damage threshold of the Ge20As22Se58 glass was determined to be higher than that of the Ge35As10S55 glass. The difference in the thermal damage threshold of the Ge35As10S55 and Ge20As22Se58 glasses and their lower value in comparison with the As2S3 glass were explained by a deviation from the stoichiometry of glass compositions and their tendency to crystallize.

Ambient humidity is an important factor to consider when maintaining dielectric films’ component performance. Herein, humidity-influenced experiments were conducted on complex spectral dielectric films based on SiO2 and K9 substrates. Firstly, complex spectral dielectric films’ spectral and surface stresses in different humidity environments were measured. Subsequently, laser-induced damage threshold measurements were carried out on these components. The experimental results indicate that the environmental humidity will induce the evolution of the internal structure of the dielectric films on the mirror, resulting in the deformation of the coating surface and a slight shift of the reflection spectrum. At the same time, the environmental humidity also greatly influences the anti-laser damage performance of the dielectric film mirror. Dielectric films based on SiO2 have excellent damage resistance in high-humidity environments. Conversely, K9-based dielectric films have better damage resistance in low-humidity environments.

Laser damage resistance of films is the key to the performance and durability of high-power laser systems. High temperature, however, often leads to a certain degree of decline in film properties. Here, aiming to explore the mechanism of laser damage under high temperatures, Nb2O5 films were prepared using sol–gel method with NbCl5 as precursor and citric acid as additive. The effect of annealing temperatures in optical performance, microstructure, surface morphologies, and chemical composition of films were studied. Further investigation was carried out of the laser-induced damage threshold (LIDT) under different in situ high temperatures of the as-deposited films. The results showed that the films had prominent optical transmittance and high LIDT. Under 293 K, the LIDT of the film was the highest of 24.8 J/cm2. The increase of temperature brought down the LIDT of the films. It was attributed to the occurrence of oxygen vacancies, the sharp increase of temperature, and rise of defects and destruction of network structure. In this study, even though the LIDT of the film decreased a lot at 523 K, it was still high up to 14.1 J/cm2, representing the great potential for applications in authentic high-temperature environments.

A multispectral anti-reflective coating of high radiation strength for laser applications in the IR spectrum for nonlinear ZnGeP2 crystals has been developed for the first time. The coating was constructed using YbF3/ZnS. The developed coating was obtained by a novel approach using ion-beam deposition of these materials on a ZnGeP2 substrate. It has a high LIDT of more than 2 J/cm2. Optimal layer deposition regimes were found for high film density and low absorption, and good adhesion of the coating to the substrate was achieved. At the same time, there was no dissociation of the double compound under high-energy ions.

The laser damage resistance of multi-layer dielectric gratings (MDGs) and metal multi-layer dielectric gratings (MMDGs) for femtosecond lasers directly determines the performance and life span of the high-energy laser system. It remains a significant challenge to predict the laser-induced damage threshold (LIDT) of MDGs and MMDGs for femtosecond lasers. Based on the nonlinear ionization and electric field intensity model, an effective method is proposed to calculate the LIDT of MDGs and MMDGs by introducing the dual temperature model. We take into account the evolutions of thermophysical parameters including the absorption coefficient, heat capacity, and thermal conductivity of the dielectric material as a function of the free-electron density and temperature. The free electron density of the conduction band combined with the electric field strength inside the grating can be calculated by the laser-induced ionization theory, more importantly, the transient distribution of the lattice temperature field generated by femtosecond laser irradiated grating excitation is obtained by the two-temperature model (TTM). This work is beneficial for guiding the design and fabrication of MDGs and MMDGs with high-LIDTs for ultra-short ultra-intense laser systems. • Predicting laser-induced damage threshold of multi-layer gratings with ionization theory and two-temp model. • Model predictions of damage thresholds are in agreement with reported experimental results. • Structural changes in multi-layer gratings affect their laser damage thresholds differently. [ABSTRACT FROM AUTHOR]

• Four hybrid materials (HfO 2 /Al 2 O 3 nanolaminate, HfO 2 /SiO 2 nanolaminate, HfO 2 -Al 2 O 3 mixture, and HfO 2 -SiO 2 mixture coatings) are investigated. • Hybrid materials show suppressed crystallization and reduced surface roughness, enabling tunable bandgaps and optical constants. • Hybrid-material-based mirror coatings are investigated and mixture-based mirror coatings have the highest LIDT. • The damage initiation mechanism of the mirror coating varies around 3 ps for laser pulses ranging from 0.5 to 8 ps.. Four hybrid materials (HfO 2 /Al 2 O 3 nanolaminate, HfO 2 /SiO 2 nanolaminate, HfO 2 –Al 2 O 3 mixture, and HfO 2 –SiO 2 mixture) and four hybrid-material-based mirror coatings are prepared via electron-beam evaporation. The refractive index (n), optical bandgaps, and microstructural properties of the hybrid materials are investigated and compared with those of pure materials. Experimental results show that the hybrid materials suppress crystallization, reduce surface roughness, and provide tunable bandgaps and optical constants. Among the four hybrid materials with similar n values, the HfO 2 –Al 2 O 3 mixture shows the largest bandgap. All the hybrid-material-based mirror coatings exhibit a higher laser-induced damage threshold (LIDT) at 8 picosecond (ps) than the conventional pure-material-based mirror coating. The HfO 2 –Al 2 O 3 mixture-based mirror coating with a relative high LIDT is used for further study of the pulse width dependence of the LIDT, and shows superior LIDT over the conventional mirror coating at 0.5 ps, 1 ps and 3 ps. Typical damage morphological features induced at different pulse widths show that the damage-initiation mechanism of the mirror coating changes around 3 ps. [ABSTRACT FROM AUTHOR]