Nonlinear change in refractive index of Co2+:ZnSe at short-pulse single-beam 1.54-μm Z-scan probing

Abstract

An experimental study and theoretical modeling of the nonlinear change in refractive index of a Co2 +: ZnSe crystal at the short-pulse single-beam probing at the wavelength 1.54 μm is reported. In the experimental conditions of negligible contributions in the index non-linearity stemming from the Kerr-effect and inhomogeneous heating, the nonlinear change in refractive index in Co2 +:ZnSe is shown to be caused by the resonant Co2 + population-perturbation effect (i.e., by the Co2 + ground-state absorption saturation). The Z-scan single-beam technique and novel theoretical approach addressing the resonant nonlinear refraction in a saturable doped medium are used, respectively, for an experimental and theoretical inspection of the phenomenon. For a set of Co2 +:ZnSe samples with different concentrations of Co2 + ions at the short-pulse (200 ns) mJ-range probing, we show that the maximal nonlinear change in refractive index is about of units of 10− 4 at the chosen wavelength.