The improved zone-plate interferometer (ZPI) is proposed to measure aspheric surface in this paper. A new computer generated hologram (CGH) zone-plate is designed and manufactured, which creates referring wavefronts for aspheric surface in the interferometer. The interferograms of ZPI are closed fringe patterns which are difficult to handle and the processing methods are researched. Two-dimensional fast Fourier transform (FFT) algorithm is proposed to extract phase. The principle and process of FFT method is described and the computer simulation proves its validity. The unwrapped phase distribution is got by the unweighted least-squares phase unwrapping algorithm. The error of aspheric surface is derived from the fitting method of Zernike polynomials. The methods are used to treat the aspheric surface measurement in experiment. The results show that the methods have achieved worthy measurement precision and have great development potential.
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