Anti-reflective nanostructured surfaces (ARSS) enhance optical transmission through suppression of Fresnel reflection at boundaries between layered media. Previous studies show random ARSS (rARSS) exhibit broadband enhancement in transmission and polarization insensitivity compared to typical optical windows. ZnSe samples with rARSS treatment were characterized (transmittance, reflectance, and angular scatter) in the mid-wave and long-wave infrared (2 - 12 μm) using a spectrophotometer. Five different random nano-roughness antireflective surfaces were tested at: normal incidence transmission and 15° angle of incidence -15 to 45° angle of reflection. The angular reflectance distribution resembles a diffuse dipole radiator, due to a finite elongated beam cross-section at the incident surface. Scattering diagrams with main and side lobes are presented. Comparing specular transmission and reflection with the scattered performance, an accurate determination of the redistribution of incident energy is obtained. Measurements of rms surface roughness using a confocal microscope is presented alongside the scattering data, for assessment of structured surface feature size effects. The results show differences in the scattered intensity, over the wavelength bands of interest, depending on the random topology of the surface. The partial-integrated scatter values were obtained, allowing the comparison of random anti-reflective surfaces to optically flat surfaces.
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