Tellurium-based far-infrared transmitting glasses

Spectroscopic investigations of molecules having their main infrared (IR) signatures at longer wavelengths require optical elements transmitting lights as far as possible in the IR region toward 20 μm and beyond. In this paper, several far-IR transmitting glass systems including Ge-In-Te, Ge-As-Te, as well as some compositions containing gallium, CsI, KI, or iodine are reported. Their glass-forming ability, thermal stability, and IR transmitting property are investigated. The gallium-containing glasses show intrinsic absorptions in the 15-20 μm region. These absorptions disappear if gallium is replaced by indium, a heavier element, but these glasses display mediocre glass forming ability. Among the systems, Ge-As-Te glasses show superior glass-forming ability and wide IR transparency. The ΔT of glasses in this system can be as great as 145°C and most of the studied glasses exhibit excellent transparency in the 3-20 μm spectral window. These glass properties compares favorably to the state-of-the-art Ge-Te-I glasses both in terms of optical quality and thermodynamic stability.