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.
Based on the theory of reflection and rotation for vector, this paper theoretically analyzes the scanning scheme by rotating the coaxial two-mirror, and constructs the transformation matrix for vector. On this basis, the relationship between the five control parameters for the scanning scheme by rotating coaxial two-mirror and the scanning trajectory (corresponding to different scanning strategies) is deeply analyzed. The scanning scheme by rotating the coaxial two-mirror designed and analyzed in this paper has the advantages of simple control (with uniform circular motion), high scanning efficiency (100%), and flexible scanning strategy and so on. It can realize the functions of rapid scanning for imaging, region ergodic searching, random or complex path for scanning and so on.
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.
In order to break through the bottlenecks for traditional optical mechanical scanning system (lower imaging frame frequency and difficult to control), this article analyzed the rapid scanning technology for imaging with high performance based on rotating of two-mirror. By using rotation of two-mirror instead of swinging back and forth for traditional scanning mode, we achieved scanning pattern with high linearity in the large field, while scanning fast, and 100% for scanning efficiency, the difficulty of system controlling is also reduced. This technology can effectively surmount the technical challenges of various optical imaging systems currently (especially for the terahertz detection system) in security screening field which requires high speed of scanning for imaging. Based on the theory of specular reflection and rotation for vectors, this article discussed and simulated several kinds of rapid scanning system for imaging by rotating of two-mirror in detail, such as Newton Telescope, Ritchey-Chretien or Gregory Telescope, dual 45 degree mirror system, fore based 45 degree mirror system,and so on. And then we obtained the quantitative relationship between the parameters of rotation for mirror controlling and the scanning trajectory in this paper. On this basis, this article compared and analyzed the performance for the series of two-mirror systems listed above which realized fast scanning for imaging, including the scanning range and scanning linearity. The results calculated in this paper can provide guidance for the selection of the structure and the optimization design of the scheme for the rapid scanning system for imaging
The reflection optical system gets more and more attention nowadays owing to without chromatic aberration and small
volume. The manufacturing and assembly/calibration technology for the coaxial reflection optical system is more mature
relative to the other reflection optical systems. But the coaxial reflection optical system will obstruct the incidence ray
especially when the field is large, which will reduce the energy entering the optical system and reduce the resolution. The
off-axis Three-Mirror Optical Systems can conquer those disadvantages of the coaxial reflection optical system, however
the manufacturing and assembly/calibration for the off-axis Optical Systems is very difficult which must use computer-aided
technology. The manufacturing and assembly/calibration technology is the main bottleneck for the off-axis Optical
Systems to the engineering application. The Author of this thesis researched the design theory of the Three-Mirror
Optical System, and then schemed out off-axis Three-Mirror and Multi-Mirror Optical System smartly using coaxial
two-mirror optical structure which conquers the disadvantage of small field and possesses of the all advantages of the
coaxial reflection optical system. This new optical system has two mirrors, one of which is a parabolic mirror with high-order
aspheric term and the other is a hyperboloid mirror with high-order aspheric term. The characteristics of this new
optical system are as follows: the F Number is 1.25, the field of view is 2°×2° and the total length is only 115mm with
coaxial assembly of the two mirrors.
In Optical System such as Multi-Channel off-axis Three-Mirror Optical System with Large Field and Small F Number, beam-split is the most important factor of the optical system design. The traditional compensating method for splitter is using tilt plate and lenses. This compensating method requires long distance between the splitter and the focal plane. On the other hand, too many lenses
using in this method will reduce the transmission efficiency of the optical system. The compensating lenses have optical-power, so we must modify the focal length of primary optical system, and then
we have to rectify the other channels to make up the changing of the focal length in this channel. In Optical System such as Multi-Channel off-axis Three-Mirror Optical System, the distance between
the splitter and the focal plane array is short, usually we don't have enough distance to place the tilted plate and lenses. So in those systems, the enough spatial distance for multi-channel beam-split is the bottleneck for the system design. For the cryogenic optical system, the compensating lenses have difficulty to work in so much different temperature. This paper advanced a new kind of compensating method for splitter, and it is an off-axis spherical lens which has falcate shape (the curvature of the two surface is approximately the same) and with no optical power. It not only can compensate the aberration of the system, and it is rather small in size, so it is propitious to the multichannel beam-split in the Multi-Channel off-axis Three-Mirror Optical System.
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