On the transparency of alkali halide crystals in the terahertz region of the spectrum

The transmission in the terahertz (THz) region (up to 3000 $\mu$m) of alkali halide monocrystals of sodium chloride (NaCl), potassium chloride (KCl), potassium bromide (KBr) and rubidium iodide (RbI), widely used in the infrared region, was studied. The dependences of the absorption coefficient of these materials in the range 0.9 – 3000 $\mu$m were obtained. Near 1000 – 3000 $\mu$m, the studied materials are transparent, which allows them to be used in THz devices of the millimeter range.