OPTIMIZED PROCEDURE FOR THE MANUFACTURE OF THIN-FILM FILTER PROTOTYPES

A simple procedure to minimize the number of trial-and-error high-vacuum depositions required to manufacture a thin film filter prototype is presented. For optical coatings obtained by thermal evaporation, the main difficulty is the accurate characterization (refractive index and thickness) of the layers under the actual deposition conditions. The proposed method is able to describe dispersion as well as inhomogeneity in the refractive index of the component layers. It requires only a suitable substrate holder attachment and standard thin film measurement equipment: a spectrophotometer and a three wavelength ellipsometer. The technique is illustrated with the development of an anti-reflection (AR) coating for glass which also includes an inhomogeneous layer.