We demonstrate a scalable photo-thermal process which enables manufacturing of infrared (IR) transmissive glass-ceramic films with gradient refractive index (GRIN) profiles. Spatiallycontrolled laser irradiation creates Pb-rich amorphous phases within Ge-As-Pb-Se glass films, which are subsequently crystallized and become high index phases upon heat treatment. The density of the high index nanocrystals is shown to be controlled by the laser irradiation power, and the extent of fraction crystallized is controlled by post heat treatment time and temperature. Both of these variables can be optimized to realize a localized effective refractive index change, enabling a spatially-modulated refractive index change up to ~ +0.1. We demonstrate IR GRIN functionality within 1 inch diameter GAP-Se films with thicknesses ranging from 1 to 40 μm, confirming the scalability of our photo-thermal process to component-relevant geometries.
The ability to employ spatially-selective control of refractive index and dispersion variation with a high magnitude of change is essential for the realization of functional infrared graded-index (GRIN) components. Thin films fabricated from multi-component GAP-Se glass-ceramic materials were processed using nanosecond laser radiation at the wavelength λ = 2 μm. Various irradiation and post-processing protocols were implemented to maximize the magnitude of the local refractive index change, and to quantify the evolution of the glass to glass ceramic ‘conversion’ on optical material physical properties. Irradiation of films possessing various thicknesses from 1 to 25 μm was performed using area-scan patterns, while the average laser power and the number of scans were varied. Irradiated materials were subsequently heat-treated, and the local refractive index was determined for different durations of the heat treatment. Depth-dependent composition and film morphology characterization of as-deposited films was evaluated, and surface morphology of the post laserprocessed and heat-treated areas was studied to evaluate effects on the photo-thermal refractive index change associated with nanocrystal formation. Initial studies demonstrated a maximum positive refractive index change of ▵n ≈ 0.07 in a broad spectral range in the infrared which scales with film thickness and exposure dose while maintaining required optical quality.
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