Numerical simulation and experimental research of using spherical reference wavefront to test aspheric surface

A practical aspheric non-null testing method of combining numerical simulation with real interferometric testing was proposed. Numerical simulation and analysis of using three typical spherical reference wavefronts which emitted by the interferometer (hereinafter referred to as spherical reference wavefronts) to test ideal aspheric surface were carried out by MATLAB. According to simulation results (simulated interferograms), the smallest one of wavefront aberrations between ideal aspheric surface and three typical spherical reference wavefronts, respectively, was selected as the wavefront under test for aspheric full aperture test; in this case, the theoretical interferogram of aspheric non-null testing was obtained by adding an appropriate amount of tilt and defocus amount to the wavefront under test. According to the theoretical interferogram, a real testing interferogram of an aspherical reflector with a diameter of 110 mm (the maximum asphericity to the vertex sphere is 6.8μm) was obtained quickly by visual observation by Zygo interferometer, and the aspheric machining error was obtained by a series processing of testing data extraction and Zernike polynomials fitting etc.. Comparison with the aspheric testing results of Taylor Hobson profilometer shows that the difference of PV and RMS value errors is less then 0.08μm and 0.02μm, respectively.