Photothermally‐Engineered Crystallization of GAP‐Se Bulk Chalcogenide Nanocomposites toward the Realization of 3D Gradient Refractive Index Profiles

Abstract Tailorability of a medium's optical properties, specifically refractive index and dispersion, is key to enabling compact optical designs. Chalcogenide glasses (ChGs) are widely used for infrared (IR) imaging applications, and the development of gradient refractive index (GRIN) optics. This work extends efforts to create and characterize 3D GRIN profiles in bulk multi‐component Ge‐As‐Pb‐Se (GAP‐Se) ChGs through spatially selective conversion of commercial glass to glass ceramic. This work extends prior efforts on bulk and film lab‐scale glass media, to that of a commercially produced material with improved optical homogeneity. Laser‐induced crystallization upon heat treatment results in the formation of high index Pb‐containing crystals that contribute to an increase in the nanocomposite's resulting effective refractive index, n_eff. The material's induced crystallinity imparted via laser exposure and heat treatment using metrology tools such as refractometry, X‐ray diffraction, FTIR, and TEM are studied. The resulting material response is quantified which is shown to be modulated via laser dose in both lateral and for the first time, axial directions enabling the first demonstration of a true, 3D GRIN profile. By comparing these outcomes to prior radial GRIN structures, the promise of these media as candidate materials for infrared systems.