Experimental system of segmented-mirror active optics

In this system, the segmented-mirror consists of three submirrors. They are hexagonal with 250 mm diagonal. The shape of each submirror is spherical with 3000 mm radius and the departure of each radius from the mean radius is less than 0.025 mm. A special S-H test device is used for co- focus measurement. It includes nine sub-apertures in three groups and each group is for a submirror. There are six displacement actuators in this system. The based unites of it are flexure hinges. The actuator is driven by a stepping motor with ten subdivisions. Six capacity displacement sensors are used in this experiment system. It is made in Tianjin University. A computer is used for data collecting, calculating and controlling. A special method for co-focus is developed in our work. By using this method the error of co-focus, i.e. the tilt error of submirror, is less than rms 0.035 arcseconds. The methods of calibration and maintaining for co-phase are also introduced in this paper. After once calibration, the diffraction limit image can be observed in about 220 mm aperture at (lambda) 650 nm, and it can be maintained about 20 minutes.