Dependence of nonlinear refractive index of ZnSe on Be and Mg content

The values of the nonlinear refractive index n₂ and the two-photon absorption coefficient β of ternary and quaternary ZnSe-based mixed crystals were extracted from the standard backward degenerate four wave mixing (DFWM) and nonlinear transmission measurements at 532 nm, respectively. Studied crystals were grown by the modified high-pressure Bridgman method. We found that the value of the nonlinear refractive index n₂ for Zn_0.79Be_0.21Se is higher than that for Zn_0.80Mg_0.20Se. However, the opposite behaviour was found in the case of two-photon absorption coefficient β for these compounds. We also found that the values of the nonlinear refractive index n₂ and the two-photon absorption coefficient β for Zn_0.83Be_0.04Mg_0.13Se are about five times lower and three times higher than that for Zn_0.80Mg_0.13Se, respectively. In the case of ternary ZnSe-based crystals we noticed that the value of the nonlinear refractive index n2 decreases with increasing Mg or Be content. However, the value of the two-photon absorption coefficient β increases with increasing Mg or Be content.