Residual aberration correction method of the three-mirror anastigmat (TMA) system with a real exit pupil using freeform surface

The goal of the letter is to reduce the manufacturing and alignment difficulty of a large-scale optical system with a real exit pupil on the premise of ensuring the high-quality imaging. An optical system residual aberration correction method by inserting a quasi-planar freeform mirror (QFM) near the exit pupil position is proposed, and here we define the residual aberration is caused by the reduced tolerance of the manufacturing and alignment. By correction analysis, the mathematical model with the QFM sensitivity matrix as the core has been established. In order to verify the residual aberration correction effectiveness and method of the QFM, a set of real manufactured mirrors shape errors and mirrors positions misalignments are introduced on a well-designed three-mirror-anastigmatic (TMA) system with an aperture of 2 meters, a focal ratio of f/12 and a field of view (FOV) of 1.2° to simulate optical system imaging quality damaged condition, and these errors cause the system imaging degeneration to RMS wavefront error (WFE) 0.331λ. Based on the QFM correction method, the system RMS WFE is corrected from the damaged imaging quality 0.331λ to 0.062λ. The QFM tolerance analysis shows that the QFM has looser precision requirements of manufacturing and alignment. By the verification, it shows this method can correct system residual aberration which caused by mirror manufacturing and alignment errors well at one time, and the TMA system has become less strict in manufacturing and alignment requirements by this way than before. The QFM correction ability and the correction method are effective.