The Thermal Change in the Nondispersive Infrared Refractive Index of Optical Materials

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, As(2)S(3) 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 DeltaN/DeltaT degrees C values of new optical materials. Measured values range from +300 x 10(-6)/ degrees C for covalent single crystal germanium to -235 x 10(-6)/ degrees C for ionic polycrystalline KRS-5.