Active correction technology for thin-mirror surface

The surface of a 400mm diameter experiment mirror was corrected by 12 active supports. In the experiment, the surface error was tested by Zygo interferometer. The force actuator of the active support is composed of displacement actuator and load cell. The response functions of each actuator are tested first, the response functions of all the actuators compose the stiffness matrix, and then the active correcting force is calculated through damp least square method. In the experiment, the ability of the active supports for correcting each aberration was analyzed, the mirror surface was corrected to generate a single Zernike polynomial wavefront of 1 (=0.6328m), and seven terms was selected for the correction finally. After 5 times correction, the 1.16 RMS surface shape error of the initial state was corrected to 0.13 RMS, near the surface quality after polishing.