Anti-reflective structured surfaces on soda-lime windows for high power laser applications

Abstract

There is a need for robust optical materials with very low reflectivity and high transmission in the visible and infrared wavelength regions for use with high energy lasers. High power continuous-wave (CW) and high pulse energy laser optical systems can suffer damage from untreated optics due to undesirable Fresnel reflections. Sub-wavelength antireflective structured surfaces (ARSS) have been shown to have a higher laser-induced damage threshold than traditional AR coatings, which are necessary for high energy (multi-kW) laser components. Previous optimization of the etching process for ARSS on fused silica, among other optical materials, has yielded controlled and repeatable parameters, resultant from formation of varying depth and density profiles by randomly removing material from the surface. The “grass-like” boundaries result in gradient-index functionalities for incident optical beams, which simultaneously reduces reflection and increases transmission of the substrate. In this study, we investigate resultant optical properties of B270 Superwhite substrates, whose surfaces are modified using reactive ion etching, in order to enhance broadband transmission and lower reflectivity, thus increasing their utility for visible and near-infrared wavelength regions. We report results for ARSS fabricated directly onto the surface of 1” diameter, B270 Superwhite optical windows. Initial trials yielded single-side random ARSS (rARSS) treated samples with transmission enhancement of up to 3% from 400-1800 nm, nearing that of rARSS enhancement of fused silica, with maximum enhancement 80% that of the theoretical value between 700-900 nm.