Optical inhomogeneity model for evaporated Y2O3 obtained from physical thickness measurement

A multiparameter fitting with additional parameters for film inhomogeneity based on transmission results is used to get film inhomogeneity information and to compare different models for film structure. For a number of evaporated materials similar results from transmission fitting have been obtained by using a model consisting of two sublayers with a constant difference in refractive indices between them, either with a thin sublayer in the contact with a substrate or with air. As additional information, we obtained the film physical thickness result from step profile measurements for an oxygen-doped Y2O3 film on a fused silica and we compared it with the fit results for this coating. The result closest to the profilometry one has been achieved for a model with a thinner sublayer in contact with the substrate. The differences are great enough to assert that Y2O3 films on a fused silica possess a higher refractive index in the first stages of growth and then, after some transition, the main material with smaller refractive index grows on it.