Light scattering from multilayer optics I Tools of investigation

We emphasize the role of correlated isotropy in the study of microroughness in high-quality optical coatings. First, cross correlation between surfaces and cross coherence between scattering sources are discussed and compared. An isotropy degree of roughness is then introduced as a quantitative value to describe the angular disorder of a surface connected with the polar dependence of scattering. We show how the frequency variations of this isotropy degree allow one to solve the inverse problem and obtain a unique solution for the scattering parameters that describe structural irregularities of the stacks. Light scattering can also be used to detect an oblique growth of the materials in thin-film form. Finally, we study the sensitivity of the investigation method to the stack parameters.