Abstract

Large coated optics are used in signal optics to maximize light gathering power so that faint objects can be revealed, and in power optics to maximize focal spot intensity. In both types of applications wavefront distortion and scattered light are of concern. Substrate specifications thus usually include optical figure, zonal tolerance, micro roughness, and allowed surface defect levels. In refractive elements, optical homogeneity is also of crucial importance. The role that single or multilayer dielectric coatings can play in modifying these specifications is not generally appreciated. For example, film thickness nonuniformities will change the apparent optical figure and may increase near angle scatter significantly. Film inhomogeneities are predicted by Elson* to have a synergistic effect on microirregularity scattering, and film-induced surface plasmon excitation may be significant in ultraviolet wavelength regions if silver or aluminum undercoatings are used. Cleanliness is crucial since coating defects may produce unacceptable scatter and even catastrophic damage. A discussion of the magnitudes of these effects, possible specifications for controlling them, and verification techniques will be given.

© 1984 Optical Society of America