Static Stripes Closed Approach

Optical interferometry is widely used in optical testing. The algorithms to process interferogram with closed fringes are studied in this thesis based on fringe coordinate transform method and two-dimensional FFT method.Based on the principle of coordinate transform method, closed fringe patterns can be converted to open fringe patterns by transforming the interferogram from the Cartesian coordinate system to a polar coordinate system. Then the fringe center can be located by means of fringe thinning. The phase distribution for the original closed-fringe pattern is obtained by inverse coordinate transformation from the polar coordinate system back to the Cartesian coordinate system.The two dimensional FFT method is applied to process closed fringe. To solve the problem of the abrupt change in the retrieved wavefront, four rectangular low pass filters are designed in frequency domain. And four separated wavefront are then stitched to obtain a smooth wavefront.According to the algorithms mentioned above, the computer program is written and the simulation analysis is performed. It shows that the errors of the two methods are withinλ/10. The interferogram of an optical lens is processed by our programs. The results are compared with those obtained by ZYGO GPI interferometer for the same lens. And it shows good agreement. Several applications are introduced and the results are presented.