DESCRIPTION OF AN INTEGRATED SCATTER INSTRUMENT FOR MEASURING SCATTERLOSSES OF SUPERPOLISHED OPTICAL-SURFACES

An instrument has been developed for measuring integrated scattering ( TIS) of low-scatter optical surfaces. In the case Of TIS measurement u sing an Ulbricht sphere, Rayleigh scattering on air was found to be th e limiting factor in improving the resolution limit of the instrument. Measures for the suppression of Rayleigh scattering are described. Th e achieved resolution limit for the integrated scattering in the refle ction hemisphere is 0.1 ppm (1 ppm = 10(-6)) of the incident light int ensity. This improved resolution offers the capability of measuring su rface roughness induced scatter losses of high quality multilayer-coat ed optics and even uncoated transparent 'superpolished' fused quartz s ubstrates. The result is given of a developed theoretical model descri bing the straylight emission of the two boundaries of a transparent su bstrate. Scatter measurement results from uncoated 'superpolished' sub strates are presented, showing scatter losses as small as 0.6 ppm corr esponding to 0.1 nm rms surface roughness.