Infrared transmission and refractive index dispersion of mixed-chalcogen Ge-Sb-S-Se glasses for use in molded lens applications

Abstract In an effort to augment thermal and mechanical properties of ternary Ge-Sb-Se glass for use in molded lens applications, mixed-chalcogen Ge27.5Sb12.5SxSe60-x glasses have been investigated in this study with a particular attention paid to refractive index dispersion as well as infrared transmission edge. Changes in Vickers hardness, glass transition temperature, dilatometric softening temperature and thermal expansion coefficient are elucidated in terms of structural evolutions that sulfur induces. Infrared transmission edge blueshifts upon the addition of sulfur, which can be nicely interpreted in connection with average bond energy and molar mass of a given composition based on a postulation that this glass behaves as a single average harmonic oscillator in shaping multiphonon absorption. Refractive index at the long-wavelength infrared range becomes more dispersive with increasing sulfur content in these sulfur-selenide glasses, and thereby their dispersion can be pinpointed via adjusting S content. The Abbe diagram in the long-wavelength infrared region is extended towards the high-dispersion side, thus enhancing practicality of the chalcogenide glasses as in the form of lens and/or filter for the thermal imaging applications.