This paper reports the index of refraction of CaWO<sub>4</sub>, CaF<sub>2</sub>, and BaF<sub>2</sub> for wavelengths from 4350 to 18 460 Å and over the temperature range - 180°C to room temperature. Measurements are made on dilute ruby at 5461 Å from -180° to 70°C. The results are applied to an interpretation of the output frequency of solid-state optical masers.
T. W. HOUSTON, L. F. JOHNSON, P. KISLIUK, and D. J. WALSH, "Temperature Dependence of the Refractive Index of Optical Maser Crystals," J. Opt. Soc. Am. 53, 1286-1291 (1963)