Accurate correction of eccentricity errors during microsphere interferometry

Interferometry is one of the most suitable method for microsphere profile inspection, and the eccentricity errors during measurement is always allowed to exit and corrected by Zernike polynomials fitting method for better dynamic response ability and higher efficiency. The common usage of coordinates on CCD instead of these on wave-front in fitting process may lead to factors errors when effective aperture is bigger than 0.25. In order to correct the eccentricity errors during microsphere interferometry precisely, the impact of normalized polar radius approximating on Zernike polynomials fitting is analyzed. An accurate correction method based on coordinates transformation is proposed, and the calibration method of NA is also given, which will be necessary in the transformation. The experiment results indicate that the PV and RMS value of corrected profile data are 0.1628λ and 0.0326λ separately, and is much more similar to the standard data where the microsphere is placed at the zero-fringe position with the PV and RMS value of 0.1636λ and 0.0332λ separately. So, it can be seen that the correction method is feasible and effective.