Polarization insensitive performance of randomly structured antireflecting planar surfaces

The transmittance polarization extinction ratio of fused silica substrates with random antireflective surface structures (rARSS) was investigated. The antireflective structures were etched on both sides of the substrates to suppress Fresnel reflection from the two surfaces, and the substrates were processed with three different sets of etching parameters, resulting in samples with three distinct sets of surface characteristics. In addition, three of the samples were fabricated with identical processes on both sides, while one was fabricated with a different process on each side. Normal incidence transmission spectra, spanning wavelengths from 300 to 1900 nm, are presented for each double-sided substrate, and variable angle of incidence polarization measurements were taken at 633 nm. Although the spectral Fresnel reflection suppression of all of the samples was measured to similar levels at normal incidence, the polarized transmittance response was found to vary considerably, correlating with the surface morphology differences and the front-to-back surface roughness similarities between the samples. Polarization insensitivity was verified from normal incidence to Brewster's angle. Comparisons with the ideal single-layer thin-film antireflection coating performance calculations show that rARSS samples are polarization insensitive over a larger range of angles and have a wide wavelength band of transmission enhancement. (C) 2018 Society of Photo-Optical Instrumentation Engineers (SPIE)