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

A method for characterizing the microroughness of samples in optical coatin g technology is developed. Measurements over different spatial-frequency ra nges are composed into a single power spectral density (PSD) covering a lar ge bandwidth. This is followed by the extraction of characteristic paramete rs through fitting of the PSD to a suitable combination of theoretical mode ls. The method allows us to combine microroughness measurements performed w ith different techniques, and the fitting procedure can be adapted to any b ehavior of a combined PSD. The method has been applied to a set of ion-beam -sputtered fluoride vacuum-UV coatings with increasing number of alternativ e low- and high-index layers. Conclusions about roughness development and m icrostructural growth are drawn. (C) 2001 Optical Society of America.