Over the past two decades, laser technology has made significant strides in scaling peak and average power levels. These advancements span a wide range of laser irradiation techniques, from ultrashort pulses to continuous waves, driving the development of various optical elements and coatings. However, the variability in optics sizes, ranging from optical fibers to meter-sized optics, and the presence of various failure modes pose challenges for laser damage testing. Consequently, there is a pressing need to align relevant laser damage testing standards to ensure the functional performance of optics. In this overview, we discuss recent standards-revision efforts aimed at revising the ISO 21254 family standards. Our primary focus is on improving accuracy and reliability by improving damage criteria, testing procedures, and results analysis methods. These efforts aim to tackle emerging challenges in laser damage testing while ensuring that standards remain compatible with modern technological developments.
ISO standards are periodically reviewed to ensure their relevance to the best industry practices. Significant advancements have been observed in laser source development and related technologies over the last two decades. These advancements encompass new irradiation regimes, ranging from ultrashort pulses to kW-class continuous wave irradiation, with substantially increased peak- and average laser power levels. This new reality also necessitates the adaptation of pertinent laser damage testing standards. As high-power laser applications introduce optical elements with unique failure mechanisms and size constraints, there is a growing need for the introduction of alternative testing methods. In this paper, we provide a brief overview of recent standardization efforts undertaken by ISO TC 172 SC 9 WG 1 for the revision of the ISO 21254 series standards - ”Lasers and laser-related equipment — Test methods for laser-induced damage threshold”. Specifically, we discuss the need for the extension of ’classical’ damage criteria, the introduction of alternative test procedures, and possible improvements in interrogation methods and analysis. The overarching goal of this paper is to promote transparency in the standardization process and inspire discussion, ultimately leading to the enhancement of accuracy and reliability in laser damage testing.
Recent studies suggest that fatigue effect in dielectric optical coatings is possibly associated with the presence of strong nonlinear absorption, however, up to now there was only indirect evidence for such hypothesis. One of the reasons for that was a technical rigor to characterize nonlinear absorption losses in optical coatings and a lack of pertinent experimental data. Recent advancement of common-path interferometry and LIDT testing allows us to overcome such limitations. In this study we examine nonlinear response and fatigue effect in single- and multilayer dielectric coatings below single shot damage threshold. Although there is no quantitative model that could predict fatigue from absorptance, we found an interesting correlation between nonlinear absorption and fatigue effect under comparable experimental conditions. These results help us to understand the mechanism of fatigue in optical coatings and possibly make more durable femtosecond optics.
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