Absorption saturation and thermo-lensing effects as the sources of nonlinear anisotropic change of refractive index in Cr 4+ :YAG at CW excitation

An experimental investigation and theoretical modeling of nonlinear refraction in a CW-pumped Cr4+:YAG crystal at wavelength 1.06µm is reported. An analysis of the processes resulting in nonlinear change of refractive index of Cr4+:YAG allows to conclude that the main contributions in the change are the effect of Cr4+ centers' population perturbation due to the ground-state absorption saturation and the thermo-lensing effect. The role of the refractive index change anisotropy stemming from both the effects is addressed for the first time to our knowledge.