Alignment of DECam-like large survey telescope for real-time active optics and error analysis

Abstract

To obtain relatively high imaging quality in the whole field of view and simultaneously create petabytes of data with a high signal-to-noise ratio, the alignment requirements for the dark energy camera (DECam)-like wide field active optics survey telescope are strict. Ensuring the real-time alignment of the system is the most important target for the future DECam-like large survey telescope due to the requirement for ellipticity of stellar image across the full field of view is much higher than the traditional telescopes. In such case, the alignment procedure needs to be designed more carefully to consider the large dynamical range and tight residual optical aberration at the same time The error of coarse alignment, influence of camera seeing, error of wavefront sensing, and interaction between the active optics and primary focus assembly and the active optics nonlinear factors, are analyzed by focusing on the DECam-like wide-field active optics survey telescope. Finally, the error of a real time active optics system is analyzed using the normalized point source sensitivity (PSSn). The PSSn of an ideal telescope is 0.9698 and the PSSn of a telescope with an alignment error is 0.8359. This work will be a good guide for the design of future large survey telescopes.