Application Of Computer Aided Alignment Technique To An Three-mirror Off-axis Optical System

With the vigorous development of space optics, the design of the space remote sensingcamera also presents the diversified and complicated. Three-mirror off-axis asphericoptical system design is the typical representative. Computer aided alignment (CAA)technique had developed in order to solve the complex alignment problem of multidegree of freedom optical system. This paper first introduced the CAA technique and itspresent situation. Summarized optical detection technique, analyzed the basic problemsand key technologies of CAA.We went into CAA technique research for three-mirror optical system, Described themathematical model based on sensitivity matrix method. The model contained the threeaspects of content, which were characteristics, pupil wavefront aberration anddisalignment of the optical system. It was certain that determinate optical system wouldbe uniquely correspond to a sensitivity matrix, which reflected the structure unitdisplacement or rotation sensitive level to the optical system aberration. We alsoanalyzed the relationship of Zernike coefficient and primary aberration. By the way, exitpupil aberrantion of Disalignment optical system obtained from autocollimationinterferometry and described by Zernike coefficients.In the paper, we applied CAA technique that based on the sensitivity matrix method toadjustment of coaxial three-mirror and off-axis three-mirror optical system. According tothe theory of vector wave aberration，the relationship between Zernike coefficient andthe field of axisymmetric system was derived and mathematical model of third mirrordisalignment was established. At the begining, the sensitive structure parameters of thethree-mirror optical system was determined. According to the steps, sensitivity matrixcondition number was calculated and the alignment tolerance was analysised as well. Forthe purpose of lowering mathematical model’s difficulties, original sensitivity-matrix hadbeen restractured and divided into two submatrixes. with this method, we finally finished an off-axis three-mirror optical system alignment with focal600mm length and7°linear field of view. And the system wave aberration is better than that0.08λ (λ=632.8nm).