The study of the optical constants of BaYF₅ and SrY₂F₈ films

Double fluoride films are used as low-refractive films in the mid-IR range of the spectrum. They have better moisture resistance and hardness then fluorides. Their using in the interference coatings requires knowledge of the optical constants of the films. The paper describes a spectrophotometric method for determining the optical constants of films with absorption based on the correction of the reflection and transmission spectra. The results of a study of optical constants also are presented in this paper: the refractive indices n and the extinction coefficients k of BaYF₅ and SrY₂F₈ films in the spectral range of 1.5–16 µm. (paper)