The measurement of surface roughness of optical thin films based on fast Fourier transform

The measurement of surface roughness of optical thin films based on fast Fourier transform (FFT) associated with a Gaussian filter was presented. The measurement of the surface roughness is performed by a Fizeau-type microscopic interferometer combined with the Matlab program to analyse the captured interferograms. The surface profile can be obtained by the fringe pattern analysis program using FFT method. In order to improve the accuracy, we normalize the fringe pattern to eliminate the background variation before using the FFT. The roughness profile is filtered by the Gaussian filter after the phase change is converted to surface height distribution. The root-mean-square value of surface roughness of optical thin films was determined by our proposed method. The results were verified by atomic force microscopy (AFM).