Co-phase error detection for segmented mirrors with ptychography

Abstract

Co-phase error detection has been extensively studied as a key technology to achieve diffraction-limited imaging for telescopes with segmented primary mirrors. This paper provides a novel method to simultaneously detect piston, tip–tilt, and decenter errors of sub-mirrors based on an extended ptychographic iterative engine (ePIE). The main components of the detection system are a transmissive specimen and a detector near the focal plane of the segmented system. The specimen is mechanically moved across the stationary beam from the telescope with adjacent positions sufficiently overlapped, and the detector then records the diffraction patterns. After retrieving the wavefront aberration of the segmented primary mirror using ePIE, the decenter errors can be calculated based on the displacement of the pupil centers of sub-mirrors and the piston and tip–tilt errors can be computed by the least square method According to a series of numerical simulations, the root mean square errors (RMSEs) of the residual co-phase errors are below 0.01 λ. The results of preliminary experiments show that the relative errors of piston error detection and decenter error detection are 1.20% and 2.08% , respectively, which validates the effectiveness of our proposed method.