Geometric Optics Applied to Rough Surfaces Coated with an Absorbing Thin Film

Abstract

The geometric optics approximation in which the interference effects are neglected has been shown to accurately predict surface reflection from random rough surfaces over a large domain of geometric parameters. In this work, the geometric optics approximation is extended to rough surfaces coated with an absorbing thin film. Multiple reflections and the effects of interference within the thin film are considered. The thin film model predictions are compared with the experimental findings for an aluminum surface coated with a thin aluminum-oxide composite film. Such comparisons made at a variety of incident angles and wavelengths indicate that the geometric optics thin film model is accurate. The approximate solutions also indicate that a significant amount of energy is absorbed by the thin film, leading to a decrease in the reflected energy. The model is used to demonstrate the strong influence of optical constants and film thickness on the reflection distribution.