Band-limited integrated scatter measurements on super polished optical mirrors

Scattering of light from a surface depends on its microroughness. In general, total integrated scattering of a surface is expressed in terms of root-mean-square microroughness (sigma(rms)) using empirical relations. These empirical relations assume that the sigma(rms) is measured over the spatial scales ranging from 0 to surface length/diameter (L). In reality, sigma(rms) will be measured over finite spatial lengths/scales that result in band-limited microroughness (sigma(bl)) and hence band-limited integrated scatter (BLIS). BLIS depends on the microroughness of surface over the finite spatial bandwidths rather than infinite spatial scales. Scatter from super polished optical mirrors peaks in specular direction and falls off exponentially. Hence, BLIS measurements in near-specular direction provide crucial information in understanding the relation between surface microroughness and scatter. Our work gives a detailed description of BLIS measurements carried out on super polished optical surfaces with different surface microroughness and a comparison between the scatter and surface microroughness measurements. (C) 2020 Society of Photo-Optical Instrumentation Engineers (SPIE)