Infrared thermooptic coefficient measurement of polycrystalline ZnSe, ZnS, CdTe, CaF_2, and BaF_2, single crystal KCl, and TI-20 glass

Abstract

An interferometric technique has been used to determine the thermooptic coefficient (dn/dT) of polycrystalline ZnSe and ZnS at 0.6328 microm, 1.15 microm, 3.39 microm, and 10.6 microm; polycrystalline CdTe and TI-20 glass at 1.15 microm, 3.39 microm, and 10.6 microm; polycrystalline CaF(2) and BaF(2) at 0.6328 microm, 1.15 microm, and 3.39 microm, and pure and europium-doped single crystal KCl at 0.6328 microm, 1.15microm, 3.39 microm, and 10.6 microm. The values were obtained over the temperature range of 25-65 degrees C and were calculated using the observed change in optical path of the samples as they were heated. Some difficulties in thermometry were encountered in the standard configuration of sample and thermocouple probe, so measurements were made in an oil bath at the shortest wavelength at which the sample was transparent to provide temperature correction factors for each sample. An empirical dispersion relation for dn/dT has also been found for the semiconductor materials. This dispersion relation is of the form dn/dT = aR(b), where R is defined as lambda(2)/(lambda(2) - lambda(g)(2)), lambda(g) is the short wavelength cutoff associated with the energy gap, and a and b are constants which are different for each material.