利用分步傅里叶算法结合坐标变换理论，建立了在光致折射率改变介质中任意形状光束的传输、聚焦模拟方法，能够用于计算任意光束形状、任意介质厚度的Z扫描开孔和闭孔拟合曲线。在薄介质和高斯光束条件下，该方法的拟合曲线与经典算法相吻合。在平顶光束情况下，该方法的拟合结果与实验数据基本一致。利用此方法测量了LiTaO3晶体的非线性吸收和非线性折射率系数，并对高斯光束和涡旋光束在厚介质中的Z扫描过程进行了分析。

Based on split-step fast Fourier transform method and coordinate transformation, we establish simulation methods of propagation and focusing of arbitrary beam shape in the light-induced refractive index change medium, in order to calculate Z-scan opening and close aperture fitted curves of arbitrary beam shape and medium thickness. Under the conditions of thin medium and Gaussian beam, the fitting curve coincides with the classical algorithm. In the case of flat-top beam, the fitting results of this method are consistent with the experimental data. By using this method, the nonlinear absorption and nonlinear index coefficient of LiTaO3 crystal are measured. Finally, the Z-scan process of Gaussian beam and vortex beam in thick media is analyzed.