Active correction experiments on a 4-m thin primary mirror

Abstract

Active optics is an important technology for improving the observation performance of large telescopes. For active optics with hard points, the hard points determine a reference plane for aberration correction. Relative movement to the reference plane will cause dents at the hard points, thus degrading the active correction effect. Herein, a compensation plane is proposed to solve the nonzero problem at hard points for surface detection and surface fitting. A series of experiments are designed on a 4-m thin mirror to illustrate the function of the compensation plane for active optics with hard points. The results show that the method is effective in avoiding the relative movement to the reference plane. With the compensation plane, the measured influence functions are more reasonable, and the dents after correction can be eliminated, which significantly reduces the fitting error of the 4-m thin mirror.