Precise alignment method of online optical testing for large-aperture mirror fabrication

A precise alignment method based on special target and fast point matching is proposed. The target includes four point-pairs for magnification calibration in peripheral area and one large-small point-pair for registration in center area. Distortion calibration of the alignment system is completed at the first time of operation. When the optical testing arm or the fabrication arm reset, the target area is focused automatically. The image captured is used to calculate the magnification of the system. Then, the large-small point-pair is located and the angle of the line through the two points is employed to adjust the swivel table, while the distance between the two points is applied for correction of the guide rail. The procedure is repeated iteratively until current location coincides with the ideal position. It is proved that the alignment accuracy of the method is about 5 μm, which is better than the precision of mechanical approach and is helpful for rapid and precise optical fabrication, and can improve the consistency of the optical testing simulation path and the practical fabrication path.