Multiangle Spectrophotometric Methods of Reflection for Determining Refractive Coefficients

— The features of the development and application of the procedures for measuring refractive coefficients based on multiangle spectrophotometric methods of reflection are considered. The effect of the shape, size, and surface treatment of the samples on their spectral dependences of the reflection is described. The possibility of determining the refraction coefficients by two spectrophotometric methods is demonstrated: using the spectrum of reflection from a single face at a small angle of light incidence close to normal and using the method of reflection of light incident at the Brewster angle. The method of reflection at an incidence angle close to normal can be applied in the case of a nonabsorbing sample characterized by an extinction coefficient not exceeding 10 –6 to 10 –4 . This is a so-called express method, because it allows us to immediately obtain the dispersion dependence of the refraction coefficient. The method allows measuring the dispersion dependences of the refraction coefficients for the samples whose shape excludes multiple reflections: plates with one polished side, plates with a large thickness polished on two sides, and prisms or plates with non-plane-parallel faces. In measurements using the Brewster method, there are no requirements for the value of the extinction coefficient of the sample (absorption) and we can use a sample of any shape, including plates with a small thickness polished on both sides. However, the resulting values of the refraction coefficients are discrete, and a large array of measurement results must be accumulated. The determined measurement accuracy of both methods was Δ = ±0.001 at a confidence probability of P = 0.95. Applicability of the spectrophotometric methods of measurement is demonstrated for the samples of a gadolinium aluminum gallium garnet, which is a crystal of a cubic system and is characterized by a single refraction coefficient. It is shown that the values of the refraction coefficients obtained by these two methods agree well within the measurement accuracy.