中频波面的旋转平移法干涉绝对检验

Abstract

Traditional absolute interferometric testing methods are all based on Zernike's polynomial fitting of tested wavefront,where the wavefront is smoothed and the mid-frequency element is lost,so they can only get the real figure of test optics.This paper adopts the rotation and displacement technique to the absolute interferometric testing of mid-frequency wavefront.The real wavefront of the test optic is separated into a rotationally symmetric component and a rotationally asymmetric component.The rotationally asymmetric component is determined by rotating the test optics for N times,while the rotationally symmetric component is determined by the pseudo shearing data through displacing the test optics.As compared with traditional absolute interferometric testing methods,there is no need to fit the wavefront of test optics with Zernike′s polynomials and can preserve whole wavefront with the proposed method.Because the rotationally symmetric component is retrieved using the even polynomials,the computation speed is enhanced and the fitting error is reduced with the mid-frequency element retained.The numerical simulation shows that the proposed method has much superiority than the traditional method and can achieve the nanometer accuracy.An experimental measurement for a flat surface is carried on with a ZYGO interferometer.The self-comparison of the experimental data is implemented by changing the pseudo shearing ratio and substituting the standard lens and the experimental data is also compared with the horizontal and vertical profiles derived from three-flat testing.Obtained results prove the accuracy of the rotation and displacement technique.