An apparatus designed and built to measure the infrared refractive index of an optical material as a function of wavelength and temperature is described. The values obtained for the thermal change in refractive index of a Si-As-Te glass, a Ge-Sb-Sa glss, As2S3 glass, and Kodak Irtran 4 are presented. Treatment of these data and literature values for other ir optical materials from a molar refraction standpoint, were used to establish an empirical relationship for predicting unknown ΔN/ΔT °C values of new optical materials. Measured values range from +300 × 10-6/°C for covalent single crystal germanium to -235 × 10-6/°C for ionic polycrystalline KRS–5.
A. Ray Hilton and Charlie E. Jones, "The Thermal Change in the Nondispersive infrared Refractive Index of Optical Materials," Appl. Opt. 6, 1513-1517 (1967)