Evaluation on the figure errors of optical aspheric surfaces after magnetorheological polishing

A method combining power spectral density (PSD) and residual errors evaluation was developed to accurately evaluate the residual figure errors on aspheric surfaces after polishing. By applying the PSD and residual errors evaluation criterion to the magnetorheological polishing (MRP) process, the relationship between residual errors and polishing processes was determined, which is helpful to establish the MRP model. A parabolic mirror was manufactured according to the criterion with a final figure accuracy up to 1/30 of the wavelength γ (γ=0.6328 μm) and residual errors less than 3/1000 of A. Experimental results indicate that the method can provide wider control degrees of freedom for decreasing figure errors during fabricating aspheric components by MRP.