Optical and Infrared Properties of Al_2O_3 at Elevated Temperatures*

Abstract

The absorption coefficient of single-crystal Al₂O₃ (sapphire) has been found to increase at most wavelengths from 0.56 to 6 μ as the temperature is increased up to 2020°C. As the temperature is increased further until the material melts, the absorption coefficient appears to increase discontinuously by a factor of about 30 or 40. The emissivity of some ceramic material which consists of more than 99% polycrystalline Al₂O₃ is greater than that of sapphire at the same temperature, but shows the same general dependence on temperature as it is heated up through the melting point.