Long-duration CW laser testing of optical windows with random antireflective surface structures on both interfaces: preliminary results

Christopher R. Wilson; Thomas C. Hutchens; Lynda E. Busse; Jesse A. Frantz; L. Brandon Shaw; Jas S. Sanghera; Ishwar D. Aggarwal

doi:10.1117/12.2317882

8 May 2018 Long-duration CW laser testing of optical windows with random antireflective surface structures on both interfaces: preliminary results

Christopher R. Wilson, Thomas C. Hutchens, Lynda E. Busse, Jesse A. Frantz, L. Brandon Shaw, Jas S. Sanghera, Ishwar D. Aggarwal

Author Affiliations +

Proceedings Volume 10627, Advanced Optics for Defense Applications: UV through LWIR III; 106270H (2018) https://doi.org/10.1117/12.2317882
Event: SPIE Defense + Security, 2018, Orlando, FL, United States

Abstract

High power laser optical systems can suffer damage from uncoated optics due to undesirable Fresnel reflections. With high power lasers, traditional anti-reflection (AR) thin-film coated optics are susceptible to localized field enhancement regions, due to multiple boundaries, and experience laser induced damage on both entry and exit interfaces. Sub-wavelength random anti-reflective surface structures (rARSS) have been shown to have a higher laserinduced damage threshold than traditional AR coatings. Previously published work detailed nanosecond-pulsed laserinduced damage on rARSS on both single surface and dual surface of optical quality, planar, fused silica substrates at 1064 nm. This study details laser fatigue testing of double-sided rARSS samples via continuous wave, 2 kW ytterbiumfiber- laser irradiation (1075 nm). Laser output was focused to increase incident intensity at the initial interface. The laser spot was focused to ~ 60-μm-diameter (1/e²) yielding a maximum power density of 70.7 MW/cm². Laser power, test duration, and testing grid were controlled externally via LabVIEW software. Damage testing sites maintained the same laser power density (70.7 MW/cm²) and varied by irradiation time, incrementally from one minute up to one hour. It was determined that double-sided rARSS substrates have a higher damage threshold than thin-film AR coatings, showing no damage of the AR structures at power densities up to 70.7 MW/cm² and laser irradiation times up to one hour at each interrogation site, while thin-film samples have been reported to fail with power density as low as 2 MW/cm².

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Christopher R. Wilson, Thomas C. Hutchens, Lynda E. Busse, Jesse A. Frantz, L. Brandon Shaw, Jas S. Sanghera, and Ishwar D. Aggarwal "Long-duration CW laser testing of optical windows with random antireflective surface structures on both interfaces: preliminary results", Proc. SPIE 10627, Advanced Optics for Defense Applications: UV through LWIR III, 106270H (8 May 2018); https://doi.org/10.1117/12.2317882

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