A wavelet filtering method for parasitic interference ring based on gradient wavefront

Interferometry is a high-precision method to test the transmitted wavefront error of lens. However, the radiuses of curvature of some part of lens are too small to produce interference with other optical surface. The resulting interference ring is parasitic in the measured wavefront. The influence of the phase and position of parasitic interference ring on the measured wavefront are analyzed in this paper. Analysis results shows that the existence of parasitic interference ring seriously affects the three-dimensional shape of the measured wavefront. To reduce its influence, a new wavelet filtering method is demonstrated and discussed. By subtract the wavelet decomposition vector of quadratic sum of XY direction gradient from the wavelet coefficients of the measured wavefront, the wavelet reconstruction decomposition vector of the real wavefront are obtained. The whole process is described in detail, and the simulation experiments are done. Compared with the median filtering and mean filtering, the result of the wavelet filtering based on the gradient wavefont is closer to the truth wavefront. This method effectively improves the wavefront filtering effect when the parasitic interference ring exists, and advantageous to guide higher quality lens processing.