傅里叶变换法分析薄膜掠入射X射线反射率曲线是获得膜层厚度、界面粗糙度等重要结构信息的分析方法之一。在傅里叶变换分析中，窗函数的选择对变换结果有重要的作用。通过对比分析“矩形窗”傅里叶变换(FFT)和“小波窗”傅里叶变换(WFFT)，发现WFFT有效抑制了FFT自相关函数出现的大量干扰峰，这对于分辨真假峰和邻近两个峰值具有重要的意义。此外，研究发现FFT和WFFT的膜层厚度分辨误差随着信号截取长度的增加呈非周期性振荡，该振荡变化与反射率曲线振荡有关，在布拉格衍射峰谷附近截断信号会得到较好的厚度分辨结果。对实验制备的单层Ni和四层Si/Ti/Ni/Ti薄膜进行了FFT和WFFT分析，验证上述结论，为分析非传统周期薄膜提供一种精确表征的方法。

Fourier transform is used to analyze grazing incidence X-ray reflectivity curve of thin film. It is a powerful analysis method for the characterization of layer thickness, interface roughness, etc. In the Fourier transform analysis, the window function has a very important effect on the transform result. By analyzing the Fourier transform of rectangular window (FFT) and wavelet window Fourier transform (WFFT), it is found that WFFT can effectively suppress the appearance of interferential peak in the FFT auto-correlation function, which is very important for identifying true and false peaks and the adjacent peaks. In addition, the film thickness error varies in aperiodic oscillation with the increasing signal length, and this change is associated with the oscillation of reflectivity curve. The ability to distinguish layer thickness is better when intercepting the reflectivity curve near the valley of Bragg diffraction peak. Ni film and Si/Ti/Ni/Ti multilayer are characterized by FFT and WFFT, which verifies the above conclusions and provides a powerful analysis method for the characterization of unconventional multilayer structures.