Abstract

The coevaporation of LaF₃ and BaF₂ has been investigated as a means of reducing the large intrinsic tensile stress of fluoride films deposited at ambient temperature. CeF₃ and BaF₂ have previously been coevaporated from a single source for stress reduction.¹ We have used coevaporation from separate sources for increased composition control and to allow separate deposition rate control for the two materials as a means of depositing gradient-index films. LaF₃ was chosen as a UV transmissive material with chemical properties identical to CeF₃. Refractive indices of the films decreased significantly. Gradient-index films with sinusoidal index profiles were then deposited by varying the BaF₂ deposition rate while maintaining the LaF₃ rate constant. This method thus allows gradient-index films with reduced stress to be deposited at wavelengths from the ultraviolet to the infrared.

© 1989 Optical Society of America