Effect of long-scale roughness in light scattering from slightly rough dielectric layers

Summary form only given.Scattering of light from slightly rough, thin, dielectric films is a classic optics problem, with a long and prestigious history. In spite of the seeming simplicity of the problem, however, and the vast literature covering the topic, no proper theoretical description or clear physical understanding exists of many of the experimental features, some of which we present here. Coherent light scattered from a slightly rough dielectric layer consists of speckle spots that arrange themselves into concentric interference rings centered around the normal to the scattering surface. In this paper, we show that the long-scale (smooth) component of the roughness spectrum (LSR) is responsible for determining the ring positions and their dependence on incidence and scattering angle, even though the presence of the interference rings is made possible mostly by the light scattered by the small-scale roughness (SSR).