Investigation on diffusion characteristics and performance of wide-spectrum chalcogenide GRIN with high refractive index

Gradient refractive index materials (GRINs) provide greater design freedom for aberration correction in wide-spectrum optical systems. In this paper, the GRINs with high refractive index and wide spectrum were successfully prepared by thermal diffusion of double-layer As₅₀Se_50-xTe_x chalcogenide glasses (ChGs). The GRINs have a refractive index spanning from 2.8 to 3.0 and a maximum refractive index difference (Δn) is 0.224. The spectral range with no significant attenuation of transmittance covers 1.5 to 18 µm. The diffusion characteristics of the GRINs were analyzed with a maximum diffusion depth of 400 μm. The values of the collision frequency factor and activation energy at different diffusion temperatures were obtained by utilizing Arrhenius law. The effect of temperature on the diffusion process was dominant over concentration. The axial refractive index distribution of GRINs is computed by converting the relationship between Te concentration and refractive index of the matrix glass. Furthermore, the dispersion characteristics of the GRINs were calculated. The Abbe number is negative, which is quite different from the dispersion characteristics presented by conventional infrared materials.