Random anti-reflection structures on large optics for high energy laser applications

Random anti-reflection surface structures (rARSSs) have been shown to increase the transmission of an optical surface to >99.9%. They are an attractive alternative to traditional thin film anti-reflection (AR) coatings for several reasons: They provide AR performance over a larger spectral and angular range, and unlike thin film coatings, they are patterned directly into the optic rather than deposited on its surface. As a result, they are not prone to delamination under thermal cycling that can occur with thin film coatings, and their laser damage thresholds can be considerably higher. In this work, an optimized reactive ion etch procedure was used to pattern rARSSs on fused silica windows, with performance optimized for high energy laser applications at 1.06 μm. We have demonstrated scale-up of this processing technique for windows with dimension of up to 33 cm. This work represents what we believe to be the largest diameter nanostructured surface on an inorganic material. The windows have been shown to have a laser damage thresholds at 1.06 μm of >100 J/cm 2 – approaching those of the substrate, and approximately five times higher than those of comparable, high quality thin film AR coatings. We present results for the AR properties and uniformity of these large windows.