Research on the control technology of PSD2 index for the 3mm ultrathin large aperture optical components

The PSD2 index of 3mm ultrathin large aperture optical components is difficult to converge effectively, which is influenced by various factors. In order to solve the problem, the measurement results of the PSD2 index were analyzed in two parts. One part was the results of the PSD2 index after removing the defocus and astigmatism, which we used to evaluate the impact of intermediate frequency errors. The other part was the surface shape PV value of the measurement area, which we used to evaluate the impact of low frequency errors. In the double-side polishing stage, the oscillating smooth polishing technology was used to smooth intermediate frequency errors of the optical surface, which eliminated the fine ripples in the PSD2 processing results. The surface shape local correction technology was used to improve the surface shape PV value of the measurement area. Through the synchronous control of the intermediate frequency and low frequency errors, the PSD2 index control for the whole surface of the optical components was realized. The RMS value of the the PSD2 index was converged from 1.38nm to 0.70nm on average.