Closed Study Of Interference Fringe Processing Method

Interferometry is of decisive position in current optical measurement development and application. Along with the development of asperical mirror technology, processing of closed interference fringe attracts people’s attention. We conduct series of research aiming at chosed interference fringe in this paper, concentrating on methods based on coordinate transforming and virtual grating moire fringe to process closed fringe.We research method based on coordinate transforming to process closed fringe and transform the closed interference fringe of Descartes rectangular coordinate system into unclosed interference fringe of polar coordinate system via luminance interpolation. Via drawing the phase of transformed unclosed interference fringe respectively by Fourier transform, Hilbert transform and fringe center method and restor it back to one of original rectangular coordinate system, we realize the phase modulation of closed interference fringe and abtain corresponding3-dimensional phase distribution. With the comparision and analysis of different phase drawing methods, we try to find a method suitable for unclosed interference fringe after coordinate transforming.We research method based on virtual grating moire fringe to process closed fringe, overlie measured interferogram to four virtual grating reference interferogram respectively with fixed phase difference generated in advance and generate third group of moire fringes containing informations of measured wave surface at a low frenquency. We abtain the moire fringes by filtering the overlied interferograms respectively in frequency domain and space domain and draw correct phase distribution via four-step phase shift algorithm. We try to aquire a range of frequency suitable for the method with the help of results at different virtual grating interferogram frequencies.According to upper contents, we carry out the computer simulation. Generated PV values of residual error wave surfaces via upper methods can reach0.1λ and their RMS values are all not exceeding0.02λ. In the same time, we process an actual interferogram of a measured lens with upper simulation, compare the processing results with its measuring results on ZYGO interferometer and abtain a suitable result.