A method for determination of refractive indices which may be applied to thin flat plates of optical materials is considered. It is particularly suited for use with materials whose refractive indices are large (>1.8), but is not limited in the range of refractive index it can determine. The method uses an interferometer to measure the optical pathlength through a sample, and is shown to have moderate accuracy: ±2 × 10-4 in refractive index for a sample 0.5 mm thick. The effect of a nonideal sample is considered, and is shown to have only a small effect on the accuracy. The method has been applied to singlecrystal barium titanate in the visible spectrum, and tabulated results are given.
Michael S. Shumate, "Interferometric Measurement of Large Indices of Refraction," Appl. Opt. 5, 327-331 (1966)