Multilayer reflecting systems based on glassy chalcogenides for infrared lasers

Materials of the Ge-As(Sb)-S(Se) system have properties which make them eminently suitable as basis of interference-type reflective coatings on mirrors of infrared power lasers. In addition to having a low absorption coefficient and wide transparency window combined with high radiation resistance, they are insoluble in water and thermally stable. They also have high mechanical strength and high resistance to cracking in a humid atmosphere, their refractive indices differing sufficiently for effective color separation by a multiheterolayer coating. The proper technology and the attainable performance characteristics of interference-type coatings consisting of glassy Ge-As-S, Ge-As-Se, Ge-Sb-Se layers were established in feasibility studies, continuous and uniform thin layers with specular surfaces having been produced from the raw materials by condensing them on cold substrates. The vacuum-evaporation process yielded films of 100 to 300 A thickness with an absorption coefficient of the order of 0.1/cm at the 10.6 micron wavelength and with a microhardness within the 230 to 450 kgf/sq m range, their crystallization and breakdown temperatures within 330 to 480 C and 450 to 500 C respectively.