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Magnetorheological polishing technology is a high-deterministic, high-precision optical ultra-precision processing technology, which is widely used in the polishing of large-aperture flat optical elements. The accuracy of magnetorheological removal function is a key factor that determines the accuracy and efficiency of magnetorheological polishing. In the process of making the removal function, it is easy to introduce spurious fringes when an interferometer is used for surface shape test. The spurious fringes will reduce the extraction accuracy of the removal function, and affect the certainty of magnetorheological polishing. In addition, the introduced spurious fringes contain complex mid- and high-frequency structures, which seriously affect the evaluation of the ability to remove function modification. In order to eliminate the spurious fringes, this paper proposes a method of removing the spurious fringes of the removal function based on the characteristic spectrum band-stop filter. First, the ZooMFFT algorithm is used to amplify the frequency spectrum to realize the effective identification of the spectral characteristics of the spurious fringes; secondly, a specific algorithm is used to eliminate only the frequency spectrum of the spurious fringes, completely retaining the frequency spectrum of the removal function itself, and does not change the valid shape of the removal function, making the spurious fringes are removed. And the Quad Flip operation is used in spectral filtering to improve the filtering accuracy. The magnetorheological making spot experiment uses a fused silica plate element with a diameter of 50mm. A static interferometer is used to measure the component wavefront data, and the tested result data contains obvious spurious fringes. Using the method described in this article, the spurious fringes are completely removed, and the morphological and removal efficiency of the removal function remains unchanged. Compared with the traditional frequency domain band-stop filter, the residual surface RMS of the spurious fringes separation is reduced from 5.45nm to 1.98nm; improve the extraction accuracy of the removal function. It can be effectively used to eliminate the spurious fringes of the magnetorheological removal function.
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