Comparative experimental study on absolute measurement of spherical surface with two-sphere method

The two-sphere method with multiple confocal measurements and a “cat's-eye” measurement is used widely in high accuracy interferometry, which can obtain the absolute surface data of the tested spherical surface. We provide a comparative experimental study on absolute testing procedures for spherical surface with two-sphere method, which include the classical Jensen method with three position measurements, the Zygo method with five position measurements and a variant of the Jensen method. The variant of the Jensen method can combine the multiple “three-position” measurements based on the fiducial method and averaging method. The repeatability of the involved absolute measurement methods is also studied by the five set experiments, and the corresponding Zernike fitting coefficients are compared in detail. The experimental results are meaningful for implementation of two-sphere method with higher repeatability in practice.

► For the two-sphere absolute testing procedures, we compare the experiment results of a variant of Jensen method with the Jensen method and Zygo method.
► The experimental results show the variant of Jensen method with averaging method and multiple fiducial method can reduce the astigmatism caused by the lateral shear of the comatic wavefront in “cat’s-eye” measurement.
► In addition, the variant of Jensen method can ensure not only the relative rotation angle at the multiple confocal measurements, but also the correct data matching.