Investigation of the Influence of Finite Aperture Size on the Z-Scan Transmittance Curve

For the nonlinear materials, not only the ratio ρ of the imaginary to the real part of the third-order nonlinear susceptibility but also the finite aperture size S exert a great influence upon the appearance of a peak on the Z-scan transmittance curve. This article investigates the ρ dependence of the critical aperture size Sc, which determines whether a transmittance peak occurs or not, and the dependence of the critical value ρc on the parameter S for the thin-sample and low irradiance limits with a Gaussian beam. These results may be applied to the adjustment of experimental conditions at all times and the assessment of the correctness of data analysis. The experiment with CS 2 seeking the critical value Sc has verified above results.