Recent progress in chalcogenide glasses applicable to infrared optical elements manufactured by molding technology

Abstract

Chalcogenide glass is a unique material applicable to infrared-transmitting optical elements that cover the atmospheric windows. It can be manufactured using molding technology, which provides mass productivity and high quality. Interest in chalcogenide glass research and developments has increased recently because of the rapid growth of the infrared optics market. This review summarizes the glass formation and properties of recently developed chalcogenide glasses. Selenium-based glasses which are widely used commercially have been introduced in comparison with infrared-transmitting crystals such as Ge and ZnSe. For sulfur-based glasses, glass-forming systems based on Ge–S and Ga–S have been described. These systems are completely free of arsenic and selenium, which are commonly used in conventional chalcogenide glasses. However, they provide glasses that are thermally stable against crystallization, and moldable. The typical spectral windows for Ge–S and Ga–S-based glasses have ranges of approximately 0.6–11 and 0.8–13 µm, respectively, although the short wavelength side strongly depends on the composition. Tellurium-based glasses are characterized by transmission in the far-infrared region, beyond 20 µm, and a refractive index higher than three. Recent studies on the temperature dependence of the viscosity and viscoelastic behaviors of chalcogenide glasses, which are both important for precision molding technology, are also discussed. Two characteristic structural relaxations have been observed in sulfide and selenide glasses.