The Index of Refraction of Germanium Measured by an Interference Method*

Abstract

A high-precision determination of the index of refraction of high-purity germanium has been made by an interferometric method in the 2.0–2.4µ region. Since the transmission of germanium in this region is very high, the optically plane parallel plate of germanium has been used as a Fabry-Perot interferometer. The change in index with temperature at 24.5°C has also been found. There is a definite variation in the temperature coefficient of refractive index at different wavelengths near the absorption edge. The Cauchy constants for the index of refraction are µ0 = 4.0385, B = 2.1345×10-9, and C = 5.363×10-17.