Optical scattering - from simple models to complex applications

Residual surface roughness of polished and coated optical surfaces gives rise to light scattering that impacts the image quality and the throughput and is therefore critical for optical lithography applications. Therefore, models are required that link structural and scattering properties as well as sensitive and accurate light scattering measurements at the wavelengths of application. These models are not just useful for predicting the impact of a given roughness onto the optical properties. In turn, scatter measurement and analysis can be used to measure roughness with several advantages regarding sensitivity, robustness, and the capability to inspect even large freeform surfaces. A variety of instruments for angle resolved and total light scattering measurements have been developed at Fraunhofer IOF. Complex laboratory instruments as well as user-friendly table-top tools will be presented briefly. Instructive examples of application are discussed ranging from the characterization of large superpolished mirror surfaces to complex multilayer systems for e.g. EUV lithography and IR components.