Laser-induced Damage Threshold Test Research Articles

Laser induced damage threshold of GaSe with antireflection microstructures at a wavelength of 5 µm.

Large GaSe crystals were grown and various antireflection microstructures (ARMs) were fabricated on their cleaved surfaces using optimized femtosecond laser ablation, which provided the antireflection effect in a wide wavelength range of 4-16µm. The influence of ARMs created on the GaSe surface on the change of the laser-induced damage threshold (LIDT) of the crystal at a wavelength of 5 μm was evaluated. The 5-µm Fe:ZnMgSe laser with the pulse duration of 135 ns was used for the LIDT test in conditions close to single pulse exposure. The measured values of LIDT of 56 ± 6MW/cm2 and 51 ± 9 MW/cm2 for two GaSe substrates, respectively, were comparable with the known data of single pulse LIDT of GaSe. The average LIDT intensities of 54 ± 6MW/cm2 and 52 ± 7 MW/cm2 for the ARMs at two GaSe plates, respectively, were close to LIDT intensities for the corresponding GaSe substrates. The ARMs with lower structural quality had lower LIDT (50-52 MW/cm2) in comparison with the high-quality ARMs (58-60 MW/cm2). High LIDT for high-quality ARMs can be caused by increased selenium content in the ARMs. In any case, all the tested ARMs on the GaSe plates with different surface quality are workable for development of widely tunable mid-infrared nonlinear optical converters.

A Laser Damage Threshold for Microscope Glass Slides

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.

Pulse temporal scaling of LIDT for anti-reflective coatings deposited on lithium triborate crystals.

Anti-reflective (AR) coatings minimize photon losses of optics when it comes to the transmission of light, thus, are broadly used for imaging and laser applications. However, the maximum output power in high-power lasers is limited by the so-called laser-induced damage threshold (LIDT) parameter of optical elements. Often AR coated nonlinear crystals are responsible for such limitations, however, LIDT data is rather scarce. Thus, only limited understanding about LIDT pulse temporal scaling laws for AR coatings exists, which also lacks the specificity about fatigue effect of distinct failure modes. To expand the present knowledge four identical lithium triborate (LBO) crystals were prepared. Each crystal had one side coated with the AR@1064+532 nm coating and the opposite side coated with the AR@355 nm coating. Multiple LIDT tests were then conducted following 1-on-1 and S-on-1 testing protocols at UV and IR wavelengths while varying laser pulse duration. Empirical scaling laws are then investigated for different failure modes and later interpreted using a numerical model.

Statistical modeling for laser induced damage threshold

Monte Carlo experiments are an efficient tool for investigation of the Laser-Induced Damage Threshold (LIDT) testing with pulsed lasers. In this study, the approach of sequential Monte Carlo search is developed for LIDT testing with bundle of laser pulses and compared with the approach of Sample Average Approximation (SAA). The likelihood ratio test is applied to accept or reject the hypothesis about the data distribution.

Laser induced damage threshold testing

Laser induced damage threshold testing

SSD detection on LIDT tested coated Fused Silica samples

Material changes and Sub-Surface Damage (SSD) under Laser Induced Damage Threshold (LIDT) testing sites were investigated on 3 diverse single layer coated transparent fused silica samples to obtain additional information on damage precursors on these samples. As a detection method, photothermal deflection technique utilizing a resonant UV laser beam was used. The local variations in UV absorption and probe beam transmittance due to previous exposure to high fluence laser pulses were strongly dependent on the coating itself and on the laser energy used during the LIDT testing. Also the obtained LIDT values differ from coating to coating. Detected effects on the coatings and substrate surface beneath ranged from small surface dislocations to complete coating damage with material transformations. Additional absorbing damage precursors were found close to the damaged sites.

Elimination of X-rays irradiated defects in fused silica by laser conditioning

Fused silica has been widely used as optical components in radiation environment. Some optical components used in these applications are frequently exposed to X-rays and other ionizing radiation, leading to the increase of optical absorption and decrease of laser-induced damage threshold, thus undermining their optical properties and operational lifetime. As on-line heating is difficult to achieve for some optical components to eliminate radiation induced defects; on the other hand off-line heating will affect the normal operation of these systems, therefore, we proposed to employ laser conditioning to eliminate radiation induced defects. The advantages of the proposed technique are demonstrated via optical absorption measurement and laser-induced damage threshold test. The experimental results show that laser conditioning can effectively reduce spectral absorption in the range from 200 nm to 320 nm in the X-rays irradiated areas and recover laser-induced damage threshold, regardless of X-rays irradiation time, 1 h or 5 h. It appears that the laser conditioning technology is potentially a useful tool to eliminate X-rays induced defects, and suited for on-line treatment in high-power laser systems.

Quantitative investigation of laser-induced damage fatigue in HfO2 and ZrO2 single layer coatings.

The decrease of laser-induced damage threshold (LIDT) of optical materials when irradiated with multiple laser pulses is an important phenomenon commonly known as the optical fatigue effect. In case of pulsed femtosecond irradiation fatigue is usually attributed to incubation of laser-induced lattice defects. In this study, standard S-on-1 LIDT test was complimented with in situ time-resolved digital holographic microscopy (TRDHM) to quantitatively investigate fatigue of catastrophic damage for HfO2 and ZrO2 single layer ion-beam-sputtered optical coatings. It was identified that ablation (critical damage) was preceded by exponential increase in optical path length visible as positive phase shift (subcritical damage). Atomic force microscopy was used to show that physical damage originates as localized 100 nm wide nanogrooves perpendicular to laser polarization. A novel link was established between LIDT fatigue and mechanical fatigue crack growth from cyclic loads which allowed construction of a unified numerical fatigue model that reproduced both S-on-1 and TRDHM experimental data.

Femtosecond Laser-Induced Damage Characterization of Multilayer Dielectric Coatings

The laser-induced damage threshold (LIDT) of optical components is one of the major constraints in developing high-power ultrafast laser systems. Multi-layer dielectric (MLD) coatings-based optical components are key parts of high-power laser systems because of their high damage resistance. Therefore, understanding and characterizing the laser-induced damage of MLD coatings are of paramount importance for developing ultrahigh-intensity laser systems. In this article, we overview the possible femtosecond laser damage mechanisms through damage morphologies in various MLD optical coatings tested in our facility. To evaluate the major contributions to the coating failure, different LIDT test methods (R-on-1, ISO S-on-1 and Raster Scan) were carried out for a high reflective hybrid Ta2O5/HfO2/SiO2 MLD mirror coating at a pulse duration of 37 fs. Different LIDT test methods were compared due to the fact that each test method exposes the different underlying damage mechanisms. For instance, the ISO S-on-1 test at a higher number of laser pulses can bring out the fatigue effects, whereas the Raster Scan method can reveal the non-uniform defect clusters in the optical coating. The measured LIDT values on the sample surface for the tested coating in three test methods are 1.1 J/cm2 (R-on-1), 0.9 J/cm2 (100k-on-1) and 0.6 J/cm2 (Raster Scan) at an angle of incidence of 45 deg. The presented results reveal that the performance of the tested sample is limited by coating defects rather than fatigue effects. Hence, the Raster Scan method is found to be most accurate for the tested coating in evaluating the damage threshold for practical applications. Importantly, this study demonstrates that the testing of different LIDT test protocols is necessary in femtosecond regime to assess the key mechanisms to the coating failure.

Femtosecond laser damage resistance of beam dump materials for high-peak power laser systems

Ultrahigh peak power laser systems require highly absorptive and high-damage threshold beam dumps, which allow safe and reliable termination of the beam path in vacuum. We present promising optical materials for high-power laser beam dump designs. In order to evaluate the optimal beam dump performance of the various materials, we characterized the optical properties of these materials and measured their damage thresholds. The tested beam dump materials include highly absorptive (>99.8 % ) Vantablack coatings and absorptive glasses with different optical densities. The laser-induced damage threshold (LIDT) tests were performed using 800-nm ultrafast laser beams with a pulse duration of 40 fs at a 1-kHz repetition rate. The LIDT test methods, such as S-on-1 and R-on-1, were used for determining the damage threshold. The Vantablack coatings showed a moderate ultrafast damage threshold while being highly absorptive and applicable on metallic substrates. The absorptive glasses with high optical density have higher damage resistance and can be used for low-repetition rate applications with the highest intensities. By comparing the optical properties and LIDT results, we discuss the suitability of these beam dump materials for ultrafast high-power laser systems.

Preparation of sol-gel ZrO2 films with high laser-induced damage threshold under high temperature.

In this study, three different types of ZrO2 films were prepared with different precursors and additives using the sol-gel method. High-temperature annealing was implemented to investigate the impact of temperature on optical properties, microstructure, surface morphologies and absorption of these films. According to the laser-induced damage threshold (LIDT) tests on films having experienced annealing and those implemented with in-situ high temperature, the ZrO2 film with ZrOCl2·8H2O as the precursor and copolymer of silicone and polyaldoxyl ether as the additive had the highest resistance to laser-induced damage. After annealing at 623 K, its LIDT was 21.4 J/cm2, while that at an in-situ high temperature of 523 K was 23.9 J/cm2. The strong high temperature resistance was likely attributed to the usage of carbon-free precursor and high temperature-resistant additive, which contributed to low carbon contents and less structural damage caused by organic matter evaporation. In this context, there were less high temperature-induced impurity and structural defects, leading to higher LIDT values. This study provided a novel method for preparing high temperature-resistant sol-gel films, which shed light upon wider potential application of sol-gel films at high-temperature conditions.

Antireflective coatings with high damage threshold prepared by laser ablation

Latest developments in the field of high power ultra-short pulse lasers have led to intensive studies dedicated to the fabrication possibility of new antireflective coatings which exhibit high damage threshold. Therefore, this study is focused on the deposition and characterization of metal oxide heterostructures followed by laser-induced damage threshold tests which evidence their application in high power laser optics. Al2O3, SiO2, and HfO2 layers are combined to obtain different heterostructures, i.e. HfO2/Al2O3/HfO2/Al2O3/HfO2 and HfO2/SiO2/HfO2/SiO2/HfO2. The metal oxide heterostructures are deposited in a controllable oxygen atmosphere, either at room temperature or high temperatures (600 °C) by pulsed laser deposition (PLD). The morphological, structural and optical properties of the as-deposited heterostructures are first investigated. Atomic force microscopy and spectroscopic ellipsometry investigations reveal a lower roughness of the heterostructures based on HfO2/Al2O3 layers grown at 600 °C as compared to those grown at room temperature. Furthermore, following the laser-induced damage threshold (LIDT) tests carried out with a Ti–Sapphire laser, higher LIDT values are obtained for the HfO2/Al2O3-based heterostructures than for the HfO2/SiO2-based heterostructures. The ability to control the morphological and structural properties of the antireflective coatings by modifying the deposition parameters of the metal oxide heterostructures demonstrates that PLD is a suitable technique for the manufacturing of antireflective coatings for high power ultra-short laser systems.

Contrasted fatigue behavior of laser-induced damage mechanisms in single layer ZrO2 optical coating.

The decrease of laser-induced damage threshold (LIDT) when exposed with high number of laser pulses is a well-known phenomenon in dielectrics. In the femtosecond regime this fatigue is usually attributed to the incubation of laser-induced lattice defects. In this work, a computational model is used to combine the data from time-resolved digital holographic microscopy measurements together with results of S-on-1 laser-induced damage threshold test in order to investigate fatigue of ZrO 2 single layer coating. Two distinct damage modes were identified and shown to follow different fatigue behaviors: formation of catastrophic damage is highly nonlinear in time, while incubation of color-change mode appears to be linear in time.

Laser damage of silica optical windows with random antireflective structured surfaces

High intensity nanosecond laser pulses induce damage on uncoated optics and antireflection (AR) coated optics with thin film boundaries. Structured surfaces with AR performance have shown higher damage resistance than conventional AR coatings. This work explores laser-induced damage threshold (LIDT) of random antireflective surface structures (rARSS), covering interfaces of planar fused silica substrates, using a 7 ± 1 nanosecond duration, single damaging pulse at 1064-nm wavelength. The rARSS treated windows were optimized for AR at 1064 nm, and transmittance of each treated interface was increased by 3.2% per ISO 13697. Incident fluence was controlled near LIDT for both entry and exit sides. Multiple locations were tested for each fluence setting in accordance with ISO 21254 1-on-1 LIDT testing. Double-sided and single-sided rARSS, orientation with both entrance-side and exit-side treatments, were tested to determine effects random structures have in damage induced by field enhancement on the exit side. Results show that rARSS on a single side of an optic have higher resistance to onset of laser damage when located at entry (structured) side. All tests resulting in damage of polished and single-sided rARSS oriented on exit side were ballistic on beam exit facet, showing surface cracks. Results from rARSS located on beam entry side (both single- and double-side treated) showed nonballistic damage and densification of rARSS features from localized melting or reflow, capping the rARSS but still preserving effective-gradient index and rARSS transmission enhancement. This suggests that the localized melting of the rARSS optic surface does not constitute damage optically, or at least not catastrophically within the prebulk damage regime. Therefore, it is possible to foresee the onset of true damage within an optical system via tracking transmission drop, and swap optics out before catastrophic system failure. The drop in transmission acts as an early warning system, making these rARSS optics an invaluable tool in high-energy laser development.

Laser resistance dependence of interface for high-reflective coatings studied by capacitance-voltage and absorption measurement

HfO2/SiO2 bilayer coatings and multilayer high-reflection coatings without and with a modified co-evaporated interface (MCEI) have been prepared. An MCEI is designed to be evaporated at an oxygen-deficient environment to achieve higher absorption than the conventional discrete interface. Capacitance-voltage measurements and absorption measurements demonstrate that an MCEI increases the trap density and leads to higher absorption. The laser-induced damage threshold and nano-indenter test results indicate that the MCEI multilayer coating exhibits better laser resistance and mechanical property, despite the larger absorption. The experimental results suggest that adhesive force between layers plays a more important role in nanosecond laser damage resistance than interface absorption.

Tunable optical properties of amorphous Tantala layers in a quantizing structure.

Plasma deposition techniques like ion-beam-sputtering (IBS) are state of the art to manufacture high quality optical components for laser applications. Besides the well optimized process and monitoring systems, the coating material selection is integral to achieve optimum optical performances. Applying the IBS technology, an approach is presented to create novel materials by the direct application of binary oxides in a quantizing structure. By reducing the physical thickness of the high refractive index material to a few nm, within a classical high-low index stack, the electron confinement can be changed. Optical characterizations of the manufactured samples with decreasing quantum well thicknesses result in an increasing blue shift of the absorption gap and offer a method to approximate the effective mass of the high refractive index material in conjunction with theoretical models. Laser-induced damage threshold tests of coating samples prepared with different well thicknesses indicate an increase of the measured threshold values with optical gap energy.

Demonstration of a 100-mJ OPO/OPA for future lidar applications and laser-induced damage threshold testing of optical components for MERLIN

In the field of atmospheric research, lidar is a powerful technology that can measure gas or aerosol concentrations, wind speed, or temperature profiles remotely. To conduct such measurements globally, spaceborne systems are advantageous. Pulse energies in the 100-mJ range are required to achieve highly accurate, longitudinal resolved measurements. Measuring concentrations of specific gases, such as CH4 or CO2, requires output wavelengths in the IR-B, which can be addressed by optical-parametric frequency conversion. An OPO/OPA frequency conversion setup was designed and built as a demonstration module to address the 1.6-μm range. The pump laser is an Nd:YAG-MOPA system, consisting of a stable oscillator and two subsequent Innoslab-based amplifier stages that deliver up to 500 mJ of output pulse energy at 100 Hz repetition frequency. The OPO is inherited from the OPO design for the CH4 lidar instrument on the French–German climate satellite methane remote-sensing lidar mission (MERLIN). To address the 100-mJ regime, the OPO output beam is amplified in a subsequent multistage OPA. With potassium titanyl phosphate as nonlinear medium, the OPO/OPA delivered more than 100 mJ of output energy at 1645 nm from 450 mJ of the pump energy and a pump pulse duration of 30 ns. This corresponds to a quantum conversion efficiency of about 25%. In addition to demonstrating optical performance for future lidar systems, this laser will be part of a laser-induced damage thresholds test facility, which will be used to qualify optical components especially for the MERLIN.

Spectral laser damage testing of optical materials

Abstract The spectral laser-induced damage of optical components was measured using a new instrument based on combining a laser-induced damage threshold (LIDT) testing procedure with angle-resolved light scattering and using a tunable optical parametric oscillator laser source. Tests on aluminum mirrors revealed a significant drop of the LIDT around 800 nm, which is not predicted by simple scaling laws. For near-infrared edge filters, remarkable changes in the LIDT around the band edge were observed, which are linked to the spectral variation of the field distribution in the interference coating.

Influence of coating thickness on laser-induced damage characteristics of anti-reflection coatings irradiated by 1064 nm nanosecond laser pulses.

The influence of coating thickness on laser-induced damage (LID) characteristics of anti-reflection (AR) coatings irradiated by 1064 nm nanosecond laser pulses was investigated. Two HfO2/SiO2 AR coatings with different physical thicknesses, 0.7 and 2.7 μm, were prepared and tested. To study the effect of coating thickness on a laser-induced damage threshold (LIDT) in isolation, electric field intensities (EFIs) at the substrate-coating interface were kept the same by using proper AR designs. Moreover, 2 nm artificial gold particles with a density of 10 mm-2 were implanted into the substrate-coating interface to achieve reliable experimental results. An optical microscope (OM) and a scanning electron microscope (SEM) were used for an online LIDT test and offline LID morphology observation, respectively. The typical LID morphology of thicker AR coatings was flat bottom craters with diameters of 20-50 μm, which can be easily observed by an online OM. For thinner AR coatings, hemispherical craters with diameters down to 1 μm were found as typical LID morphology by a SEM. However, these tiny craters could not be observed by an online OM. Moreover, such tiny craters did not grow with subsequent pulses, so they did not degrade the functional laser damage resistance of the thin AR coatings. When identified with an online OM, the LIDT of thinner AR coatings is found to be about two times higher than the thicker ones, and large delamination was mainly found as the LID morphology of AR coatings with high fluence. When observed with a SEM, the LIDT of thin AR coatings with tiny craters was over 60% lower than the LIDT of thick AR coatings, which agrees with the model that less energy is required to form smaller LID craters of thinner coatings.

Laser-induced damage threshold tests of ultrafast multilayer dielectric coatings in various environmental conditions relevant for operation of ELI beamlines laser systems

Increasing the laser-induced damage resistance of optical components is one of the major challenges in the development of Peta-watt (PW) class laser systems. The extreme light infrastructure (ELI) beamlines project will provide ultrafast laser systems with peak powers up to 10 PW available every minute and PW class beams at 10 Hz complemented by a 5-TW, 1-kHz beamline. Sustainable performance of PW class laser systems relies on the durability of the employed optical components. As part of an effort to evaluate the damage resistance of components utilized in ELI beamlines systems, damage thresholds of several optical multilayer dielectric coatings were measured with different laser parameters and in different environments. Three coatings were tested with 10 Hz and 1 kHz pulse repetition rates, and the effect of a cleaning treatment on their damage resistance was examined. To explore the damage threshold behavior at different vacuum levels, one coating was subject to tests at various residual gas pressures. No change of damage threshold in a high vacuum with respect to ambient pressure was recorded. The effect of the cleaning treatment was found to be inconsistent, suggesting that development of the optimal cleaning treatment for a given coating requires consideration of its specific properties.