Large polycrystalline optical germanium Ge:Na plates with improved optical parameters and their application

Abstract

It has been experimentally shown that transmission and scattering of IR radiation by Na-doped coarse-grained large germanium plates are the same as of Ge:Na single crystals and exceeds the parameters in the commonly used optical germanium Ge:Sb grown from the same raw material. Being based on experimental results, a conclusion has been made that the nature of the dopant in Ge:Na is a decisive factor defining its optical parameters, along with the usual requirements of high purity of the raw material, resistance values below about 20 Ohm.cm and a sufficiently large grain size (for polycrystalline material). It is assumed that, most likely, Na in Ge:Na, contrary to Sb in Ge:Sb, doesn't form impurity clouds that scatter the incident IR radiation. The advantages of the polycrystalline Ge:Na as a material for IR optics were proved when using it for industrial manufacturing the protective screens for night vision systems.