Model-based fine phasing of segmented mirror using Chebyshev segmented piston-tip-tilt modes.

ABSTRACT

On-orbit cophasing is essential for high-resolution imaging of space telescopes with a segmented primary mirror. A model-based fine phasing method for a segmented mirror is proposed and demonstrated in this Letter. The tip-tilt error is related to the second moment of spot intensity, and the piston error is related to the Strehl ratio. Chebyshev segmented piston-tip-tilt (CSPTT) modes are used to express cophasing errors to suppress the effect of imaging noises. The CSPTT modal coefficients are estimated by the "2N + 1" algorithm that introduces bidirectional biases for each mode's estimation. The proposed method is proved robust to image noises and figure errors.