Accurate calibration of misalignment in high-precision spherical surface testing

Based on the detailed analysis of the Zernike aberrations of wavefront errors, including the wavefront defocus and tilt, introduced by test surface misalignment in the high-precision spherical surface testing, a method for the misalignment calibration using Zernike coefficients was put forward in this paper. The experimental validation of the proposed calibration method was carried out with Zygo interferometer, in which a high-numerical-aperture spherical surface was tested by introducing both the wavefront defocus and tilt. The measured data were then respectively processed with the proposed method and the traditional calibration method for removing the tilt and defocus errors, by which the feasibility of the proposed method was demonstrated. This method is effective for calibrating the spherical aberration introduced by misalignment of high-numerical-aperture spherical surfaces, and an accuracy of 0.002λ (λ is the optical wavelength in the test) was achieved in the experiment. The proposed method can help lower the requirement of the adjusting precision of mechanical devices as well as the skill of testing personnel, which can be applied to the high-precision measurement of spherical surface.