Procedure to characterize microroughness of optical thin films: Application to ion-beam-sputtered vacuum-ultraviolet coatings

Measurements over different spatial-frequency ranges are composed into a single power spectral density (PSD) covering a large bandwidth. This is followed by the extraction of characteristic parameters through fitting of the PSI) to a suitable combination of theoretical models. The method allows combine microroughness measurements performed with different techniques, and the fitting procedure can be adapted to any behavior of a combined PSI). - The method has been applied to a set of ion-b sputtered fluoride vacuum-LTV coatings with increasing number of alternative low- and high-index la. Conclusions about roughness development and microstructural growth are drawn.