A simple scatter method for optical surface roughness and slope measurements. Roughness of polished fused silica

For supersmooth optical surfaces, the equation relating diffusely scattered light to roughness and slope parameters assumes a simple form. Measurements of rms roughness and slope for such surfaces can be made with an instrument which accepts a solid angle much smaller than 2π steradian. Measurements made on fused silica surfaces yield values as low as 0·23 nm and 3·8 × 10 −4 rad.