Modeling of light scattering from optical surfaces

Optical instruments are normally designed under the assumption of perfectly smooth optical surfaces. However, this is never the case in practice: surface imperfections such as scratches, digs and roughness as well as contaminations by small particles produce stray light that needs to be considered when analysing the performance of optical instruments. This is not only relevant for the high-end optical systems such as space optics. In many illumination systems such as light guides stray light is induced intentionally. In any case the surface properties should be modelled and their impact evaluated correctly. The key quantity for modeling light scattering from surfaces is the bidirectional scattering distribution function (BSDF). In this talk we concentrate on BSDF models available in commercial software. We present typical scenarios in which a detailed modelling is needed. Beside the theoretical discussion, we compare two experimental approaches to determine the BSDF—by measuring the angle-resolved scatter and by evaluating AFM-images of the surface topography. We discuss limitations of these approaches and propose solutions to overcome their drawbacks.