Infrared Gradient Refractive INdex (GRIN) Materials Through Fast Solid‐Solid Na⁺/Ag⁺ Ionic Exchange in Chalco‐Halide Glasses

AbstractIn this work, a new two‐step process is developed by exchanging Na+ and Ag+ to create a radial GRIN infrared lens. The first step consists in introducing a high amount of silver by solid‐state ion exchange in the surrounding of the glass sample when the second one allows for controllable diffusion of Ag+ within the center of the sample by single heat treatment. Evolution of the refractive index and ∆n between the two extreme compositions of the GRIN are determined as function of the wavelength, predicting a ∆n of 1.42 × 10−1 at 10 µm. Qualitative characterization of the sample reveals the formation of a GRIN chalcogenide glass transparent in the MWIR and LWIR, presenting no detrimental crystallization of residual metallic silver on the edge of the sample. Wavefront measurement allows to quantitatively characterize the 10 mm diameter IR GRIN as a polynomial profile with a ∆n of 1.8 × 10−1 at 10.6 µm.