Determination of the bulk and surface absorption coefficients of highly transparent solids in the wavelength range of $CO$ laser radiation

A calonmetric system was used to determine the spectral dependences of the bulk and surface absorption coefficients of highly transparent solids, which were in the $10^{-4}-10^{-6}$ cm${}^{-1}$range at wavelengths of $5,3-6,2\mu m$. The example of thallium chloride was used to show that a tunable $CO$ laser could be used as a light source. The absorption spectra of optical ceramic and single-crystal samples of $TlCl$ were found to have impurity bands at about 1620 and 1730 cm${}^{-1}$: these bands were respectively due to the deformation vibrations of water and valence vibrations of the $C=O$ bond.