Moisture-dependent anisotropic effects in optical coatings

Abstract

Anistropic effects which depend on or are influenced by adsorbed moisture are discussed for films deposited at oblique incidence. Form birefringence reduces as water enters voids in a coating and the process of water transport is itself anisotropic. In some films water patches with an elliptical shape are formed during an early stage of the adsorption process. The distribution of optical radiation scattered from moisture patches in such a film is expected to be anisotropic. As metal–dielectric–metal filters were used in some of the observations, anisotropy of reflectance was investigated for both silver and aluminum.