INO340 active optics algorithm

An active optics algorithm is developed for the Iranian National Observatory 3.4 [m] telescope (INO340). The primary mirror (M1) and the secondary mirror (M2) are considered flexible and rigid, respectively. M1-Support consists of 60 active axial actuators (AAC), 32 passive lateral actuators (LAC), three axial hard-points (AHP), and three lateral hardpoints (LHP); and an accurate hexapod supports M2. M1 surface shape and M2 positions are actively controlled using an active optics system (AOS) to reach the best image quality. Correction can be done using either a look-up table in open-loop control or the wavefront error in closed-loop control. This paper presents the algorithm and the strategy of INO340 active optics. In this regard, relevant extracted matrices for the INO340 active optics algorithm are derived. The Shack-Hartmann sensor probes the accumulated aberrations and provides a square matrix as feedback. By decomposing the aberrations into the Zernike polynomials, tip-tilt, defocus, and coma aberrations are eliminated by adjustment of M2 positions and other aberrations are removed by deforming the flexible M1. The effective mechanical modes of M1 are selected based on the AACs' force amplitude, and root mean square (RMS) of the residual surface. The percentage of residual surface error and set of axial forces are shown for each mechanical mode. As a result, mechanical modes No. 1 to 9 and No. 12 to 16 can be corrected. Finally, the algorithm is used to remove the remained aberration after the polishing process, which shows the residual surface after compensation and the required set of AACs' force.