Study of transmittance dependence closed-aperture Z-scan curves in the materials with nonlinear refraction and strong absorption

In this paper we report, the measurement of the nonlinear refraction and absorption in the bulk of CdS, ZnS, ZnO, GaN, and ZnSe (direct band gap crystals), CdI2 and PbI2 (indirect band gap crystals) with frequency double Nd:YAG laser. Further the characteristics of closed aperture (CA) Z-scan transmittance curves have been studied in detail when the third-order nonlinear refraction and absorption are simultaneously present, and both of which can be independently positive or negative. It was found that for the purely non linear absorption, the transmittance curve exhibits a completely symmetric shape and for nonlinear refraction the curve shape is anti-symmetric. We found that whether the peak–valley/valley–peak and valley or peak structure exists or not, depends on the coupling factor (ρ  ) which is the ratio of the imaginary part χI(3) to the real part χR(3) of the third-order nonlinear susceptibility χ(3).