Abstract

An ideal optical coating applied to an ideal surface will control the intensity and phase of an optical ray in reflection, transmission and absorption without affecting its direction of propagation. Real optical coatings deposited on substrates with imperfect surfaces scatter radiation away from the specular direction. The scattering of light in a multilayer is caused by defects, inhomogeneities, and roughness of the interfaces between the layers. Defects include particles of foreign materials or voids which are embedded in the structure. Inhomogeneities include local variations in the density, and thus the refractive index of a layer. Although defects and inhomogeneities may be treated theoretically, there is more to be gained by their elimination through careful manufacturing techniques than by understanding their contribution to scattering. The roughness of interfaces in multilayers is difficult to control and survives the most gallant experimental efforts. The theoretical treatments of scattering by optical coatings predict the spectral and angular content of scattered light as functions of the deviations of the interfaces from perfect planes.

© 1992 Optical Society of America