Interfacial roughness and related scatter in UV-optical coatings

For a variety of UV optical coatings, surface roughness was measured by use of an atomic-force-microscope (AFM) to study its dependence on the film material and thickness, coating design, and deposition process. After analyzing the corresponding power spectral density functions, we propose a simple classification model for coatings according to the contributions of substrate roughness and intrinsic film roughness to the scattering. Results of scattering measurements on different types of coatings are presented and are found to be in good agreement with predictions based on the AFM data. Consequence for a scatter reduction strategy are discussed.