Comparative study of the roughness of optical surfaces and thin films using atomic force microscopy, x-ray scattering, and light scattering methods

The surface roughness of polished glass substrates as well as metal an dielectric coatings is studied using atomic force microscopy, hard and soft x-ray scattering at the wavelength (lambda) equals 0.154 nm and 4.47 nm, and light scattering (LS) at (lambda) equals 325 nm. It is demonstrated that all the methods, permitting the determination of PSD functions in partly overlapping, partly different ranges of spatial frequency, are in a good agreement in spite of different physical principles underlying the methods. The possible reasons for some differences in the PSD functions determined form different measurements are discussed. The main of them are a more difficult interpretation of LS data when dielectric coatings are present and a limitation on the angular range of hard x-ray scattering measurements imposed by the applicability of the perturbation theory used for experimental data processing.