Geometric optics applied to rough surfaces coated with an absorbing thin film

The geometric optics approximation in which the interference effects are ne glected 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 wit h an absorbing thin film, Multiple reflections and the effects of interfere nce within the thin film are considered. The thin film model predictions ar e compared with the experimental findings for an aluminum surface coated wi th 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 sig nificant amount of energy is absorbed by the thin film, leading to a decrea se in the reflected energy. The model is used to demonstrate the strong inf luence of optical constants and film thickness on the reflection distributi on.