Infrared transmission properties of sapphire, spinel, yttria, and ALON as a function of temperature and frequency

Experimental characterization of the bulk absorption properties of sapphire, spinel, yttria, and ALON as a function of temperature is accomplished using a Bomem DA3.02 vacuum Fourier transform spectrometer and a heated cell. The measurements are performed between 2 and 20 microm from room temperatures to 775 K. Spectra of two samples of different thicknesses are ratioed to reduce surface effects and to provide a direct measure of the bulk extinction coefficient. Absorption coefficient and reflectivity data are used to determine parameters in a multiphoton absorption model. The model has proved valid up to the melting temperature of the material. This model provides an accurate means of interpolating and extrapolating the measurements to give a comprehensive characterization of intrinsic absorption properties with frequency and temperature (in the multiphonon region).