Compositional screening of chalcogenide glass for use as molded lens: an exemplary case of ternary Ge-Sb-Se glass

Abstract

Thermal imaging in the long-wavelength infrared (8‒12 μm) range is blooming in diverse civilian sectors. In order to meet requirements specific to these new applications, lens assembly should be advanced in terms of performance enhancement and size miniaturization as well as cost reduction. Unlike its crystalline counterparts, chalcogenide glass is not only tolerable in compositional adjustments but also viscoelastic upon mechanical loading at a proper temperature. These two merits basically allow opportunities for the compositional engineering of moldable (or imprintable) chalcogenide glasses with dissimilar optical constants. The compositional screening process needs to take into account thermomechanical properties required for the precision glass molding technique as well as optical properties prioritized for lens applications. In an effort to pave an efficient way to compositional optimization of chalcogenide glass for use as molded lens, we employ ternary Ge-Sb-Se system, i.e. a prototypical chalcogenide glass forming system. The compositional range experimentally screened for use in the molded lens applications is elucidated in terms of unempirical glass structure related parameters such as mean coordination number and average bond energy. These guidelines derived from the structural evolutions of Ge-Sb-Se glass are useful in prescreening other chalcogenide glasses that are subject to molding and/or imprinting processes.