TEMPERATURE COEFFICIENTS OF THE REFRACTIVE-INDEX FOR CANDIDATE OPTICAL WINDOWS

The temperature coefficients of the refractive index for various crystalline and polycrystalline materials-Al2O3 (sapphire), Y2O3 (Yttria), La2O3-doped Y2O3, MgAl2O4, and ALON (a proprietary ceramic composed of aluminum, oxygen, and nitrogen)-were determined from measurements of optical thickness as a function of temperature using a Michelson interferometer operating at 0.633 mum. For temperatures between 23 and 500-degrees-C, the first-order coefficients ranged from 8.3 X 10(-6)/-degrees-C for pure yttria to 14.6 X 10(-6)/-degrees-C for ALON. Measurements of NaCl and Al2O3 samples using this technique are in agreement with published data.