This paper analyzes the basic theory of rapid rotating scanning scheme for the off-axis 45° parallel two-mirror system, and constructs the transformation action matrix of optical vector in the rotating scanning process. Based on simulation with MATLAB, the relationship between the four control parameters of rotating scanning scheme for the off-axis 45° parallel two-mirror system and the scanning trajectories is analyzed in-depth, and the basic conditions of the control parameters are determined to achieve various scanning strategies. The performances of two scanning strategies (Linear scanning in any direction and Elliptical scanning in different ranges) are analyzed in detail. The scanning scheme discussed in this paper has the advantages of simple control, high scanning efficiency (100%), and flexible scanning strategy and so on by scanning with mirror rotating. It can realize the functions of rapid scanning for imaging with high linearity, region ergodic searching, random or complex path for searching and so on.
When the off-axis two reflection optical system is applied to the infrared system, it faces the contradiction between Wide FOV and small F#. The off-axis three reflection system can increase field of view in the symmetrical direction but difficult in the asymmetric direction. This paper explores a method to solve this problem. First, a three-mirror reflection system is designed with off-axis field of view and aperture according to requirements of field of view and F# in the symmetrical direction. The field of view in the asymmetric direction is set at about 1°, and the aperture diaphragm is placed in front of the image plane to form Lyot Stop. Then the main mirror is planarized and removed that the secondary mirror and the tertiary mirror can form an Anti-telephoto structure, the field of view is increased in the asymmetric direction. Finally, the dimensional constraints are established to avoid occlusion and adjust and optimize this system. According to this method, a double off-axis two reflection optical system suitable for infrared imaging is designed with the f-number 1.6, the field of view 7°×7°, the distortion less than 3% and the imaging quality close to the diffraction limit.
The aperture diaphragm of the Cook-TMA optical system is set on the secondary mirror, which improves the symmetry of the system. It has features of large field of view and small f-number, and suitable for infrared optical system. However, the system has no Lyot stop and low efficiency of cold diaphragm. A new method is proposed in this paper. First, Cook-TMA off-axis three-mirror reflection system is designed according to the requirements of field of view and f-number. Second, the aperture diaphragm is moved to a place behind the tertiary mirror and before the image surface, which becomes Lyot stop in fact. At this time, the beam obstruction problem arises. Starting with large f-number, we adjust and optimize gradually to solve the obstruction problem until the f-number meets the requirements. According to this method, three-mirror reflection optical system with off-axis field of view and off-axis aperture is designed with the f-number 1.6 , the field of view 11° by 1°, grid distortion less than 2%, imaging quality closed to the diffraction limit, which is suitable for imaging in infrared wavelength band.
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