Active cophasing and aligning testbed with segmented mirrors

Abstract

An active segmented cophasing imaging testbed with a high accurate optical adjustment and control in nanoscale is set up. A two-dimensional dispersed fringe analysis method is used to calculate the piston error between the adjacent segments. Segments alignment of tip-tilt is fulfilled by overlapping diffraction pattern centroids of the individual segment on the focal plane. The cophasing errors are corrected by sensitive micro-displacement actuators under a computer closed-loop control. A FISBA interferometer is introduced to evaluate that a final total residual surface error of about 0.08λ RMS and the residual piston error of 0.026λ RMS are achieved (λ = 633 nm).