Thickness and refractive-index changes associated with photodarkening in evaporated As2S3 films

Employing a sensitive variable angle interference technique the changes in thickness Δl/l and in refractive index Δn/n accompanying the photo-induced shift of the optical absorption edge toward longer wavelengths were determined in evaporated As2S3 films. The irreversible heat or light-induced structural change was found to be associated with a decrease in thickness Δl/l=0.011±0.001 and an increase in refractive index Δn/n=0.045±0.005. Changes of l and n associated with the reversible photodarkening effect were found to be less than 0.2 and 0.5 percent, respectively.