Adjustment of refractive index of Ge-Ga-Se glass via Te addition for infrared-imaging applications

Abstract

After assessing compositional dependence of thermal and optical properties of Ge-Ga-Se glasses, we introduce Te, via replacing Se, into Ge₂₅Ga₅Se₇₀ and Ge₃₅Ga₅Se₆₀ (mol%) glasses in an attempt to enhance their refractive index. In the case of Se-deficient Ge₃₅Ga₅Se₆₀ composition, vitrification is achieved for Te content up to 20 mol%. In the case of Se-sufficient Ge₂₅Ga₅Se₇₀ composition, however, formation of bulk glass is realized only when Te content ranges from 25 to 45 mol%. Being proportional to Te content, refractive index of Ge₂₅Ga₅Se₃₀Te₄₀ glass is measured to approach 2.855 at 10 μm, which is far superior to that of any commercialized selenide glasses for infrared-imaging applications. This compositionally tailored Ge₂₅Ga₅Se₃₀Te₄₀ glass is further verified to be compatible with the conventional precision glass molding process, and infrared-imaging performance of the resulting molded lens is as excellent as the existing selenide-glass-based lenses.