Index of refraction measurement on sapphire at low temperatures and visible wavelengths

The ordinary and extraordinary refractive index of two samples of sapphire, which differed in the way each was grown, was measured. The measurements were made over a wavelength range of 477-701 nm and a temperature range of 20-295 K. A three-term Sellmeier dispersion equation was fit to the data to permit refractive-index interpolation within several parts in 10(4). The data of index versus temperature were fit to a model and the results of dn/dT versus temperature are given along with certain physical constants that were extracted from the model.