D. Raiser, J. Holburg, K. Mann, Ricardo Martins, A. Tighe
Molecular contamination due to outgassing of organic materials in vacuum can be a source of significant degradation for space equipment, especially for sensitive optical instruments. Thus, on-ground contamination measurements in vacuum are essential to ensure the flight hardware cleanliness and for making in-flight performance predictions. A suitable detection technique shall work in-situ and in real-time, i.e. it shall be possible to measure the real-time build-up of contamination layers of a few nanometers and less on surfaces in vacuum in the presence of an outgassing source. In this paper we address a new experimental setup for controlled contamination and high-sensitivity spectroscopic analysis of the contaminants on representative material for typical space optics. The central method of choice for the detection of organic contaminants incorporated in this setup is laser-induced fluorescence (LIF), which provides the demanded distinguishability of the applied contamination species. Different excitation wavelengths in the UV spectral range are used. LIF measurements are accompanied by in operando verification of amount and species of the contaminants by a thermoelectric quartz crystal microbalance (TQCM) and a mass spectrometer (MS). This parameter study aims for exploring the laser parameter dependent detection limits and the temperature-dependent condensation process with respect to various substrate-contaminant combinations, in order to reveal strategies to prevent contamination for space applications.
{"title":"Ultra-sensitive laser-based contamination detection for space applications","authors":"D. Raiser, J. Holburg, K. Mann, Ricardo Martins, A. Tighe","doi":"10.1117/12.2602232","DOIUrl":"https://doi.org/10.1117/12.2602232","url":null,"abstract":"Molecular contamination due to outgassing of organic materials in vacuum can be a source of significant degradation for space equipment, especially for sensitive optical instruments. Thus, on-ground contamination measurements in vacuum are essential to ensure the flight hardware cleanliness and for making in-flight performance predictions. A suitable detection technique shall work in-situ and in real-time, i.e. it shall be possible to measure the real-time build-up of contamination layers of a few nanometers and less on surfaces in vacuum in the presence of an outgassing source. In this paper we address a new experimental setup for controlled contamination and high-sensitivity spectroscopic analysis of the contaminants on representative material for typical space optics. The central method of choice for the detection of organic contaminants incorporated in this setup is laser-induced fluorescence (LIF), which provides the demanded distinguishability of the applied contamination species. Different excitation wavelengths in the UV spectral range are used. LIF measurements are accompanied by in operando verification of amount and species of the contaminants by a thermoelectric quartz crystal microbalance (TQCM) and a mass spectrometer (MS). This parameter study aims for exploring the laser parameter dependent detection limits and the temperature-dependent condensation process with respect to various substrate-contaminant combinations, in order to reveal strategies to prevent contamination for space applications.","PeriodicalId":202227,"journal":{"name":"Laser Damage","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2021-10-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"116098301","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Fused silica an optical material of choice for high energy laser applications offers a wide range of advantages in the UV and NIR wavelength range. Increasing laser performance (especially with critical fluences) require detailed information on laser induced damage threshold of the optical material itself, and not just the coating. Therefore, S-on-1 measurements according to ISO 21254-2 were commissioned from two different, experienced, and well-respected laboratories. The resulting LIDT (laser induced damage threshold) values are discussed in the context of current publications and differences are worked out. The measurements focus on the ns-pulse regime at 1064 and 355nm. The results differ up to a factor of 10 between different laboratories. In comparison to the literature study, we noticed a spread of measured values around a factor of 20. Non-binding recommendations of the standard as well as the optical setup have significant influence on the obtained LIDT values. However, depending on the optical design of the application, one or the other optical setup with the corresponding LIDT value can be relevant. In this respect there is no such thing as a single, generally applicable value. Nevertheless, a standard should enable material comparisons under sufficiently standardized conditions.
{"title":"Bulk LIDT variances of fused silica: a material developer's perspective","authors":"F. Nürnberg, B. Kühn","doi":"10.1117/12.2599501","DOIUrl":"https://doi.org/10.1117/12.2599501","url":null,"abstract":"Fused silica an optical material of choice for high energy laser applications offers a wide range of advantages in the UV and NIR wavelength range. Increasing laser performance (especially with critical fluences) require detailed information on laser induced damage threshold of the optical material itself, and not just the coating. Therefore, S-on-1 measurements according to ISO 21254-2 were commissioned from two different, experienced, and well-respected laboratories. The resulting LIDT (laser induced damage threshold) values are discussed in the context of current publications and differences are worked out. The measurements focus on the ns-pulse regime at 1064 and 355nm. The results differ up to a factor of 10 between different laboratories. In comparison to the literature study, we noticed a spread of measured values around a factor of 20. Non-binding recommendations of the standard as well as the optical setup have significant influence on the obtained LIDT values. However, depending on the optical design of the application, one or the other optical setup with the corresponding LIDT value can be relevant. In this respect there is no such thing as a single, generally applicable value. Nevertheless, a standard should enable material comparisons under sufficiently standardized conditions.","PeriodicalId":202227,"journal":{"name":"Laser Damage","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2021-10-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"114521734","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
M. Lenzner, Amir Khabbazi Oskouei, L. Emmert, M. Jupé, T. Willemsen, M. Steinecke, D. Ristau, W. Rudolph
When designing femtosecond laser mirrors, one tries to minimize the peak intensity within the high-index layers to increase the laser-induced damage threshold. Typically, the optimization procedure utilizes the electric field distribution in the layer stack generated by monochromatic irradiation. This approach is sufficient for certain structures like high-reflectors based on quarter-wave films. More complex structures require to take into account the exact evolution of the pulse parameters such as peak intensity and duration within the multi-layer system. We exemplify this by discussing a merit function that can be included in femtosecond optics design.
{"title":"Spatio-temporal evolution of femtosecond laser pulses in dielectric multi-layers controlling the damage behavior","authors":"M. Lenzner, Amir Khabbazi Oskouei, L. Emmert, M. Jupé, T. Willemsen, M. Steinecke, D. Ristau, W. Rudolph","doi":"10.1117/12.2600528","DOIUrl":"https://doi.org/10.1117/12.2600528","url":null,"abstract":"When designing femtosecond laser mirrors, one tries to minimize the peak intensity within the high-index layers to increase the laser-induced damage threshold. Typically, the optimization procedure utilizes the electric field distribution in the layer stack generated by monochromatic irradiation. This approach is sufficient for certain structures like high-reflectors based on quarter-wave films. More complex structures require to take into account the exact evolution of the pulse parameters such as peak intensity and duration within the multi-layer system. We exemplify this by discussing a merit function that can be included in femtosecond optics design.","PeriodicalId":202227,"journal":{"name":"Laser Damage","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2021-10-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"114517129","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
U. Wegner, J. Meier, D. Rompotis, R. Secareanu, M. Emons, B. Monoszlai, M. Lederer
We are presenting our observations regarding laser induced degradation of coated optics exposed to the burst-mode pulsetrain of the optical pump-probe laser systems (PP-laser) at the European X-ray Free Electron Laser (EuXFEL). Degradation happens on HR and AR coatings from various suppliers during the course of prolonged exposure to the 515 nm, 800 fs burst-mode radiation. Since the lasers typically operate 24/7, coatings degrade within a few weeks to several months, depending on the requested burst lengths and number of pulses and hence integrated burst energies. Reduced performance of pointing- and pulse energy-stability and a drop of average power of the non-collinear optical parametric amplifiers (NOPAs) result. As user facility, the EuXFEL strives to maximize up-time and to reliably provide high quality x-ray and optical laser beam lines for user experiments, which is compromised to some extent by the observed coating degradation. In this report we show our investigations into the effect so far. In collaboration with the coating manufacturer Layertec GmbH, an improved mirror coating was found, which prolongs optics life time by nearly a factor of 3.
{"title":"Degradation of optical coatings induced by high-intensity, 515 nm, sub-picosecond burst-mode laser beam","authors":"U. Wegner, J. Meier, D. Rompotis, R. Secareanu, M. Emons, B. Monoszlai, M. Lederer","doi":"10.1117/12.2598668","DOIUrl":"https://doi.org/10.1117/12.2598668","url":null,"abstract":"We are presenting our observations regarding laser induced degradation of coated optics exposed to the burst-mode pulsetrain of the optical pump-probe laser systems (PP-laser) at the European X-ray Free Electron Laser (EuXFEL). Degradation happens on HR and AR coatings from various suppliers during the course of prolonged exposure to the 515 nm, 800 fs burst-mode radiation. Since the lasers typically operate 24/7, coatings degrade within a few weeks to several months, depending on the requested burst lengths and number of pulses and hence integrated burst energies. Reduced performance of pointing- and pulse energy-stability and a drop of average power of the non-collinear optical parametric amplifiers (NOPAs) result. As user facility, the EuXFEL strives to maximize up-time and to reliably provide high quality x-ray and optical laser beam lines for user experiments, which is compromised to some extent by the observed coating degradation. In this report we show our investigations into the effect so far. In collaboration with the coating manufacturer Layertec GmbH, an improved mirror coating was found, which prolongs optics life time by nearly a factor of 3.","PeriodicalId":202227,"journal":{"name":"Laser Damage","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2021-10-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"132578544","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
The recent development utilizing automatic microscopy to identify damage sites on an optic for damage mitigation at the National Ignition Facility (NIF) has resulted in a large set of damage dataset for growth analysis. In this work we will examine how the pre and post installation damage sizes are used to analyze the cumulative probability of growth for damage sites that have been exposed to multiple laser shots. The analysis can form the basis to derive single-shot probability growth behavior of fused silica damage site as a function of size.
{"title":"Analysis of cumulative probability of growth of damage sites at the National Ignition Facility","authors":"Zhi-min Liao, C. Miller, D. Cross, C. Carr","doi":"10.1117/12.2598943","DOIUrl":"https://doi.org/10.1117/12.2598943","url":null,"abstract":"The recent development utilizing automatic microscopy to identify damage sites on an optic for damage mitigation at the National Ignition Facility (NIF) has resulted in a large set of damage dataset for growth analysis. In this work we will examine how the pre and post installation damage sizes are used to analyze the cumulative probability of growth for damage sites that have been exposed to multiple laser shots. The analysis can form the basis to derive single-shot probability growth behavior of fused silica damage site as a function of size.","PeriodicalId":202227,"journal":{"name":"Laser Damage","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2021-10-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"131720826","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
R. Negres, C. Stolz, G. Batavičiūtė, A. Melninkaitis
This year’s competition is a continuation of the 2020 thin film damage competition conducted with nanosecond (ns) laser pulses and aimed to survey state-of-the-art visible high reflectors in the femtosecond (fs) pulse length regime. The requirements for the coatings were a minimum reflection of 99.5% at 0 degrees incidence angle at 532 nm. The fs-laser source available for testing in 2021 delivered pulses at 515 nm; as a result, to accommodate both ns- and fs-damage tests on the same samples, the latter tests were conducted at an incidence angle of 25 degrees to re-center the reflection spectral band of the coatings, i.e., a blue shift from 532 nm to 515 nm. The choice of coating materials, design, and deposition method were left to the participants. Laser damage testing of samples received in 2020 and new sample submissions in 2021 was per- formed at a single testing facility using the S-on-1 standardized test protocol with a 200-fs pulse length laser system operating at 5 kHz in a single-longitudinal mode. A double-blind test assured sample and submitter anonymity. The damage performance results (LIDT), sample rankings, details of the deposition processes, coating materials and substrate cleaning methods are shared. These experiments enabled not only direct comparison among the participants but also the performance contrast in two different pulse length regimes. We found that different deposition methods and coating materials yield comparably high laser resistance in the fs-pulse regime. Namely, hafnia/silica, hafnia/alumina/silica or tantala/alumina/silica multilayer coatings were the most damage resistant under exposure to fs-laser pulses within the coating deposition groups. In contrast, hafnia/silica coatings by e-beam were identified as best performers in the ns-pulse regime.
{"title":"515-nm, femtosecond laser mirror thin film damage competition","authors":"R. Negres, C. Stolz, G. Batavičiūtė, A. Melninkaitis","doi":"10.1117/12.2597206","DOIUrl":"https://doi.org/10.1117/12.2597206","url":null,"abstract":"This year’s competition is a continuation of the 2020 thin film damage competition conducted with nanosecond (ns) laser pulses and aimed to survey state-of-the-art visible high reflectors in the femtosecond (fs) pulse length regime. The requirements for the coatings were a minimum reflection of 99.5% at 0 degrees incidence angle at 532 nm. The fs-laser source available for testing in 2021 delivered pulses at 515 nm; as a result, to accommodate both ns- and fs-damage tests on the same samples, the latter tests were conducted at an incidence angle of 25 degrees to re-center the reflection spectral band of the coatings, i.e., a blue shift from 532 nm to 515 nm. The choice of coating materials, design, and deposition method were left to the participants. Laser damage testing of samples received in 2020 and new sample submissions in 2021 was per- formed at a single testing facility using the S-on-1 standardized test protocol with a 200-fs pulse length laser system operating at 5 kHz in a single-longitudinal mode. A double-blind test assured sample and submitter anonymity. The damage performance results (LIDT), sample rankings, details of the deposition processes, coating materials and substrate cleaning methods are shared. These experiments enabled not only direct comparison among the participants but also the performance contrast in two different pulse length regimes. We found that different deposition methods and coating materials yield comparably high laser resistance in the fs-pulse regime. Namely, hafnia/silica, hafnia/alumina/silica or tantala/alumina/silica multilayer coatings were the most damage resistant under exposure to fs-laser pulses within the coating deposition groups. In contrast, hafnia/silica coatings by e-beam were identified as best performers in the ns-pulse regime.","PeriodicalId":202227,"journal":{"name":"Laser Damage","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2021-10-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"115884804","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Niklas Praetzsch, Hermann Sturzebecher, N. Pirch, F. Fischer, C. Haefner
In Laser Powder Bed Fusion (LPBF), there are high demands on the cleanliness of the protective window (PW). During processing, however, process-by-products may accumulate on the PW surface and thereby change the process boundary conditions. In this work, a methodology to assess the condition of PWs in a LPBF machine using a line scan camera is presented. Image processing is used to detect the degree of contamination on the PW surface by using a thresholding algorithm. The line scan camera results are further validated by ex-situ microscopic images of the contaminated surface of the PW. The higher resolution of these images enables the quantification of particle count and size distribution. Moreover, the influence of the contamination degree of the PWs on the beam quality is investigated. A laser focus shift of up to 22.6 mm against the direction of beam propagation within a caustic measurement as well as a minor decrease in relative density of 0.08 pp in 316L samples were detected due to the contamination. Based on this work, methods for monitoring the health condition of PWs in LPBF can be derived.
{"title":"Detection of contamination of protective windows in Laser Powder Bed Fusion by means of a line scan camera","authors":"Niklas Praetzsch, Hermann Sturzebecher, N. Pirch, F. Fischer, C. Haefner","doi":"10.1117/12.2598589","DOIUrl":"https://doi.org/10.1117/12.2598589","url":null,"abstract":"In Laser Powder Bed Fusion (LPBF), there are high demands on the cleanliness of the protective window (PW). During processing, however, process-by-products may accumulate on the PW surface and thereby change the process boundary conditions. In this work, a methodology to assess the condition of PWs in a LPBF machine using a line scan camera is presented. Image processing is used to detect the degree of contamination on the PW surface by using a thresholding algorithm. The line scan camera results are further validated by ex-situ microscopic images of the contaminated surface of the PW. The higher resolution of these images enables the quantification of particle count and size distribution. Moreover, the influence of the contamination degree of the PWs on the beam quality is investigated. A laser focus shift of up to 22.6 mm against the direction of beam propagation within a caustic measurement as well as a minor decrease in relative density of 0.08 pp in 316L samples were detected due to the contamination. Based on this work, methods for monitoring the health condition of PWs in LPBF can be derived.","PeriodicalId":202227,"journal":{"name":"Laser Damage","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2021-10-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"126622980","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
We report on the clear difference in the behavior of laser-matter interaction of tightly focused high-intensity pulses with the bulk of solids when chirping and tuning the wavelength of the laser driver from near-IR to mid-IR. In transparent dielectrics, laser wavelength scaling leads to the change in the heating mechanism which, in turn, leads to a weak dependence of the plasma formation threshold on the pulse duration in mid-IR (4.6 μm) and a significant impact in the case of the near-IR (1.24 μm) excitation. In the case of semiconductors, the ionization mechanism remains within the framework of the multiphoton approximation, but an increase in the photon order for excitation by mid-IR pulses leads to a decrease in delocalization processes and losses in the prefocal region.
{"title":"The effect of chirp and wavelength for ultrafast bulk modification of solids with tightly focused laser pulses","authors":"E. Mareev, E. Migal, F. Potemkin","doi":"10.1117/12.2603492","DOIUrl":"https://doi.org/10.1117/12.2603492","url":null,"abstract":"We report on the clear difference in the behavior of laser-matter interaction of tightly focused high-intensity pulses with the bulk of solids when chirping and tuning the wavelength of the laser driver from near-IR to mid-IR. In transparent dielectrics, laser wavelength scaling leads to the change in the heating mechanism which, in turn, leads to a weak dependence of the plasma formation threshold on the pulse duration in mid-IR (4.6 μm) and a significant impact in the case of the near-IR (1.24 μm) excitation. In the case of semiconductors, the ionization mechanism remains within the framework of the multiphoton approximation, but an increase in the photon order for excitation by mid-IR pulses leads to a decrease in delocalization processes and losses in the prefocal region.","PeriodicalId":202227,"journal":{"name":"Laser Damage","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2021-10-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"131852746","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Yuhai Li, Q. Bai, R. Shen, Peng Zhang, L. Lu, Xiao-Qing Yuan, X. Miao, W. Han, Hao Liu, Lin Huang, Caizhen Yao
Organic contaminants on optical components can degrade optical properties, thus limiting the energy enhancement of highpeak- power laser systems. It is still challenging to remove organic contaminants on the SiO2 sol-gel antireflection film and avoid damage. In this work, a low-pressure air plasma in-situ cleaning technique and a chemical reaction model of plasma cleaning were proposed to study the removal of organic contaminants. The optical properties of sol-gel AR films suffered from organic contaminants were evaluated by transmittance and laser-induced damage threshold, which recovered completely after 5 minutes of plasma cleaning without damage. Meanwhile, the hydrophilicity of the surface and the surface free energy were significantly increased after plasma treating. Surface composition analysis indicated that the CH and C-C bonds were reduced considerably, while abundant C=C and C=O bonds were produced after plasma cleaning. Optical emission spectrum analyzed the reactive species and its concentration in the air plasma as a reference for simulation. The chemical interaction process of oxygen radicals with organic contaminants was simulated by reactive molecular dynamics. The results can provide a guide for optical components in-situ cleaning.
{"title":"In-situ cleaning organic contaminants on SiO2 sol-gel antireflection film by low-pressure air plasma","authors":"Yuhai Li, Q. Bai, R. Shen, Peng Zhang, L. Lu, Xiao-Qing Yuan, X. Miao, W. Han, Hao Liu, Lin Huang, Caizhen Yao","doi":"10.1117/12.2599668","DOIUrl":"https://doi.org/10.1117/12.2599668","url":null,"abstract":"Organic contaminants on optical components can degrade optical properties, thus limiting the energy enhancement of highpeak- power laser systems. It is still challenging to remove organic contaminants on the SiO2 sol-gel antireflection film and avoid damage. In this work, a low-pressure air plasma in-situ cleaning technique and a chemical reaction model of plasma cleaning were proposed to study the removal of organic contaminants. The optical properties of sol-gel AR films suffered from organic contaminants were evaluated by transmittance and laser-induced damage threshold, which recovered completely after 5 minutes of plasma cleaning without damage. Meanwhile, the hydrophilicity of the surface and the surface free energy were significantly increased after plasma treating. Surface composition analysis indicated that the CH and C-C bonds were reduced considerably, while abundant C=C and C=O bonds were produced after plasma cleaning. Optical emission spectrum analyzed the reactive species and its concentration in the air plasma as a reference for simulation. The chemical interaction process of oxygen radicals with organic contaminants was simulated by reactive molecular dynamics. The results can provide a guide for optical components in-situ cleaning.","PeriodicalId":202227,"journal":{"name":"Laser Damage","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2021-10-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"130999429","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
C. Stolz, J. Weng, Tsion Teklemarim, M. Brophy, P. Kupinski
One third of the exchanged final turning mirrors on the National Ignition Facility have been laser damaged by 3ω (351nm) target backscattered light. The mirrors are spectrally complex hafnia and silica multilayer dichroic coatings with high 1ω reflection for the forward propagating beam and low 3ω reflection to suppress propagation of target backscatter. Alumina, a wider bandgap high index material than hafnia, was selected to improve the 3ω laser damage resistance despite a lower refractive index. A 2-4x improvement in 3ω LIDT was demonstrated with adequate 1ω laser damage resistance. Nodule ejection was the dominate laser damage morphology. An 18% decrease in the refractive index between alumina and hafnia results in coating designs that are 3x thicker. Similarly, a decrease in refractive index also decreases the angular bandwidth resulting in increasing the number of mirror types from two to six over an angular range of 16 degrees. The significant improvement in 3ω LIDT has justified beginning a scale up demonstration to full aperture (0.3m2).
{"title":"Evaluation of alumina and silica coating materials for the NIF final turning mirrors","authors":"C. Stolz, J. Weng, Tsion Teklemarim, M. Brophy, P. Kupinski","doi":"10.1117/12.2598577","DOIUrl":"https://doi.org/10.1117/12.2598577","url":null,"abstract":"One third of the exchanged final turning mirrors on the National Ignition Facility have been laser damaged by 3ω (351nm) target backscattered light. The mirrors are spectrally complex hafnia and silica multilayer dichroic coatings with high 1ω reflection for the forward propagating beam and low 3ω reflection to suppress propagation of target backscatter. Alumina, a wider bandgap high index material than hafnia, was selected to improve the 3ω laser damage resistance despite a lower refractive index. A 2-4x improvement in 3ω LIDT was demonstrated with adequate 1ω laser damage resistance. Nodule ejection was the dominate laser damage morphology. An 18% decrease in the refractive index between alumina and hafnia results in coating designs that are 3x thicker. Similarly, a decrease in refractive index also decreases the angular bandwidth resulting in increasing the number of mirror types from two to six over an angular range of 16 degrees. The significant improvement in 3ω LIDT has justified beginning a scale up demonstration to full aperture (0.3m2).","PeriodicalId":202227,"journal":{"name":"Laser Damage","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2021-10-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"116098828","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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