Co-phasing experiment of a segmented mirror using a combined broadband and two-wavelength algorithm.

In this paper, a broadband phasing algorithm is combined with a two-wavelength phasing algorithm to detect the piston error of a segmented mirror with the advantages of long range, high precision, and fast detection. Moreover, an active optics co-phasing experimental system of the segmented mirror is built to verify the algorithm's effectiveness. The segmented mirror consists of four hexagonal segments, with flat-to-flat lengths of 100 mm and radii of curvature of 2000 mm. First, a Shack-Hartmann sensor and piezoelectric actuators are used to finely co-focus the segmented mirror. Then, the broadband phasing algorithm is used to reduce the piston error of the segmented mirror to several micrometers. Finally, the two-wavelength phasing algorithm is used to reduce the piston error of the segmented mirror to zero. The experimental results show that the measurement accuracy is better than 26 nm, and the adjustment accuracy is approximately 55 nm, which demonstrates that the combined algorithm is valuable for segmented-mirror co-phasing measurement and adjustment.