Thermally Matched Chalcogenide Glasses with High Refractive Index Contrast for Infrared Graded-Index Lenses

Abstract

Infrared graded-index (GRIN) lenses are desirable for realizing miniaturization and lightweight of infrared imaging systems. Chalcogenide glasses have excellent infrared transparency, good rheological property, and large refractive index range, making them preferred materials for infrared GRIN lenses. In this work, aiming to find thermally matched chalcogenide compositions with high refractive index contrast for preparing GRIN glasses, characteristic temperatures, thermal expansion coefficient and refractive index of Ge-As-Se and Ge-As-Se-Te glasses are studied, and the suitability of optimized chalcogenide powders for co-pressing into high-transparency glasses is evaluated. It is found that Ge20As20Se20Te40 and Ge12As22Se66 glasses have similar softening temperature (247oC vs 249 oC), reasonably difference of thermal expansion coefficient (3.8 ppm/K), and large refractive index contrast (~0.48). The glass powders with composition xGe20As20Se20Te40-(1-x) Ge12As22Se66 can be hot-pressed into glass disks with good transmittance at the same temperature and pressure, demonstrating the prospect of the compositions for preparing infrared GRIN glasses.

Keywords: Graded-index lens, Chalcogenide glass, Hot pressing, infrared imaging