Improved method for misalignment calibration in interferometric testing of spherical surface

According to the high-order approximation model of misalignment in interferometric testing of spherical surfaces, an improved method based on Zernike polynomials fitting was proposed to calibrate the misalignment aberrations of test spherical surface. With the numerical aperture of test surface and Zernike polynomial coefficients of measured raw surface data, both the low-order and high-order aberrations introduced by misalignment can be acquired and removed from the measured raw surface data. Then high-precision calibration of spherical surface misalignment can be realized. Experimental validation was conducted with Zygo interferometer, and a high-numerical-aperture test spherical surface was tested to demonstrate the feasibility of the method. The high calibration precision with root-mean-square and peak-valley values 0.001λ and 0.011λ, respectively, was gained. Ultra-high misalignment calibration precision can be realized according to experimental results. The method requires no foreknowledge about the specific adjusting error and is convenient for automatic processing, and lowers the accuracy requirement on the adjusting mechanism for the spherical surface under test in testing system.