Multi-Angle Spectrophotometric Reflectance Methods for Determining Refractive Coefficients

The experience in developing and applying methods for measuring the refractive coefficients of high and middle category crystals based on multi-angle spectrophotometric reflectance methods (using the reflection spectrum from one face at a close-to-normal angle of incidence of light and the reflectance method where light falls at the Brewster angle) is peresented. Advantages and limitations of the methods and requirement to samples are described. It is shown that the reflectance method at a close-to-normal angle of incidence is applicable to optically isotropic media. The Brewster angle method is applicable to high and middle category crystals. The measurement accuracy is determined for both methods. Their applicability is verified for high- (Gd₃Al₂Ga₃O₁₂ : Ce) and middle category (La₃Ga_5.5Ta_0.5O₁₄) crystals.