Abstract
A standard is proposed for specifying surface roughness of optical elements to enable the control of scatter produced at optical surfaces. This scatter reduces system MTF, and signal-to-noise ratio. Such a standard must not be arbitrary but must be based on form, fit or function rather than convenience since available instruments can measure scatter or roughness. A roughness standard that can provide this is the one-dimensional surface Power Spectral Density (PSD), S1(fx)' (p,m3), where f is a one-dimensional spatial frequency (pm-1). The standard consists of four numbers: A the proportionality constant (.1m3+13), B a frequency exponent, C the minimum spatial frequency (Am-1) and D the maximum spatial frequency (Am-1). PSD can be bound by the function A/0 over the spatial frequency range C to D. From this PSD the Bidirectional Reflectance Distribution Function (BRDF), RMS roughness and autocorrelation length can be calculated. An experiment was designed to create a database of A and B for frequently used IR materials, glasses and reflective materials. Experimental data appears to confirm the potential viability of such a standard as refined by later validations and data additions. Variations of this standard exist for BRDF and two-dimensional PSD.
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