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Fresnel reflection losses are detrimental to performance of optical systems. Not only do reflections diminish transmission, but rebounding energy can lead to system damage and catastrophic failure in high-energy and highpower laser systems. Suppression of Fresnel reflections by conventional thin-film coatings does not suit all applications, especially high-energy laser (HEL) systems, as foreign material coating can burn off or delaminate. Sub-wavelength structured surfaces minimize reflectivity by gradual change of refractive index from ambient to substrate. Consisting of no foreign material, anti-reflective structured surfaces (ARSS) offer a viable method to suppress reflectivity. ARSS on fused silica (SiO2) windows have been previously shown to exhibit high laser-induced damage thresholds (LIDT), comparable to bulk material LIDT. This study further explores the application of ARSS on low-dispersion crown/soda-lime glass, specifically SCHOTT B270. Random anti-reflective structured surfaces (rARSS) were fabricated by reactive ion etching a surface of 1-inchdiameter, 2-mm-thick, B270 Superwhite optical windows. Transmission results taken via an Agilent CARY 60 spectrometer on single-side processed windows demonstrate greater than 95.0% and 94.5% transmission across 700- 800 and 530-1000 nm wavelength bands, respectively. A 100% enhancement of transmission from single facet in this band would theoretically result in 95.6% overall transmission. Therefore, we demonstrate transmission enhancement factor of 85% for one facet etched, as compared to untreated B270. Scanning electron microscopy (SEM) was used to analyze sub-micron surface morphology of the rARSS B270 windows. Randomly orientated “sponge-like” surface features 20-200 nm in width were observed. Successful high broadband transmission enhancement of B270 has been demonstrated using novel rARSS treatment.
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