Closed aperture z-scan technique using the Fresnel–Kirchhoff diffraction theory for materials with high nonlinear refractions

Abstract

The close aperture z-scan experiment was carried out using Fresnel–Kirchhoff diffraction theory, and the special shape of close z-scan curves is determined based on the properties of the diffraction ring pattern. As an experimental case, the nonlinear refractive index of a dye (acid blue 9) is calculated using the mentioned method for the first time. Some new applications of the Fresnel–Kirchhoff diffraction theory are also explained which may be useful to characterize the nonlinear optical properties of materials. Finally, a numerical relation is evaluated to simply calculate the nonlinear refraction index in cases with high nonlinearity orders.