SPECTRAL EMISSIVITY OF OPTICALLY ANISOTROPIC SOLID MEDIA

This work determines the spectral emissivity of a semi-infinite uniaxi al medium in vacuum. If the optic axis is normal to the surface, then, for many materials and wavelengths, such as rutile between 10 and 25 mum, the directional and hemispherical spectral emissivities of the me dium can be approximated, with an error of less than 10 percent, as th ose of an isotropic medium possessing the ordinary optical constants. In contrast, if the optic axis is parallel to the surface, the directi onal and hemispherical spectral emissivities can be predicted only by accounting for the optical anisotropy of the medium. Measurements of t he directional emissivities of rutile crystals conform to the theoreti cal predictions.