Accurate determination of optical nonlinear absorption coefficients by the combination of reflection and transmission open-aperture z-scan measurements

In most z-scan measurements, the Fresnel reflection loss is generally negligible, which is reasonable for transparent samples or materials with small nonlinear coefficients. However, for semi-transparent samples with low transmission or samples with large nonlinear coefficients, the Fresnel reflection loss attributed to the nonlinear effect is large and must be considered in z-scan measurement and data fitting. In this study, we proposed a method and established the corresponding theoretical model and experimental configuration of combining the reflection open-aperture z-scan and the transmission open-aperture z-scan measurements to determine accurately the nonlinear absorption coefficients by considering the Fresnel reflection loss. The Sb2Te3 film was used as an example. The nonlinear absorption coefficient was experimentally measured and theoretically fitted by our model. The theoretical fitting curves are highly consistent with the experimental data, indicating that the theoretical model and the configuration of the experimental setup can reasonably and feasibly obtain an accurate nonlinear absorption coefficient in actual applications.