The optical properties of high-porosity quartz ceramics

The effective absorption coefficient and the radiation diffusion coefficient are determined for high-porosity quartz ceramics of three types prepared by a production process involving the use of foaming agents. A laser photometer is used for measuring the normal hemispherical transmissivity of cylindrical samples of different thicknesses and the angular dependence of the directional hemispherical transmissivity of one of the samples. Results are given for wavelengths of $0.63$, $1.15$, and $3.39$ $\mu$m. The thus obtained data are used to calculate the dependence of the bihemispherical reflectivity of a flat layer on the layer thickness