Laser Damage Testing of Windows with Anti-reflection Structured Surfaces for High Power Continuous-wave Near- Infrared Laser Applications

摘要

High power continuous-wave (CW) and high pulse energy laser optical systems can suffer damage from untreatedoptics due to undesirable Fresnel reflections. With high energy pulse lasers, traditional anti-reflection (AR) thin-filmcoated optics are susceptible to localized field enhancement regions, due to multiple boundaries, and experience laserinduced damage on both entry and exit interfaces. Sub-wavelength anti-reflective structured surfaces (ARSS) havebeen shown to have a higher laser-induced damage threshold than traditional AR coatings. Previously published workdetailed nanosecond-pulsed laser-induced damage on planar fused silica (FS) substrates with random ARSS (rARSS)treatment (λ=1064 nm). This study details and compares laser damage and fatigue testing of rARSS treated FS viacontinuous-wave, 2 kW irradiation (λ=1075 nm). Gaussian laser output was focused to～ 60-μm-diameter (1/e~2), toincrease incident intensity, yielding a maximum power density of ～70.7 MW/cm~2. Laser power and duration werecontrolled while monitoring the window’s optical transmission and entry/exit surface temperatures. CW durations atmaximum power up to 5 min were used. Peak temperatures were recorded for untreated FS, as well as double sidetreated rARSS samples.