Scattered-Light Measurements Of Optical Surfaces

Measurements of the angular distribution of scattered light produced by specially-polished optical components are reported. The components were six 12-cm aperture coronagraph objective mirrors and two 20-cm coronagraph objective lenses. For each test the component was illuminated with white light and the magnitude of the scattered flux measured at several field points. It was not feasible to separate surface and body scattering of the lenses, so that these measurements represent the combined contributions. Successive recoatings and tests of the mirrors has led to the conclusion that the residual roughness of the substrate polish is the dominant parameter that determines the magnitude of the scattered flux. Dark ground and phase contrast measurements qualitatively support this conclusion. The fractional contributions of integrated scattered light of the lenses and mirrors are found to be of the same order, although the functional relationships are significantly different over the angular range measured.