In the field of space optics, the compact freeform optical imaging system with small F number can realize the miniaturization and lightweight of the load, which is beneficial to enhance the ability of target recognition. In this paper, according to the vector aberration theory and the principle of Gaussian brackets, the error evaluation function is constructed by the primary wave aberration coefficients and focal length constraint of the system, and the dynamic weight is used to limit difference in the order of magnitude between various aberrations, which is conducive to rapid convergence in the process of solving the initial structural parameters. In order to achieve the compactness of the system, the circular layout is adopted. The unobstructed initial structure of the off-axis reflective system with conic surfaces is obtained through Particle Swarm Optimization (PSO) algorithm, and the off-axis three-mirror freeform optical system with a highly compact layout is obtained after optimization. In addition, considering the difficulty of freeform surfaces manufacturing, add the manufacturability constraint to the optimization process to control the degree of departure between the aperture edge of the freeform surfaces and the conic surfaces in real time. Compared with the optical system obtained without manufacturability constraints, the difficulty of manufacturing is effectively reduced.
Compared with traditional coaxial multi-reflection imaging systems, the off-axis imaging system using optical freeform has many advantages, including high design freedom, small optical system size and high energy utilization. Nowadays, optical freeform surfaces have been widely utilized in imaging and non-imaging optical systems. But correspondingly, freeform machining is more difficult than spherical and aspherical optical reflectors. In the turning process, toolpath plays a critical role because it will determine the accuracy of the machined surface. The conventional methods to generate toolpath include constant-angle method, constant-arc-length method and the combination of constant-angle and constant-arc-length methods. This article proposes a new method based on an Adaptive Point Design Algorithm (APDA) to generate a series of cutting points. It will generate the cutter’s toolpath based on the tangential height changes of the ideal surface. Through the simulation, the algorithm is verified that it can achieve the same accuracy when reducing the amount of data by about 40%, compared with the traditional constant-angle method. This makes freeform machining faster and provides the basis for precision machining of large-aperture freeform surfaces.
Considering the demand of high-resolution imaging and dark targets detection, large-aperture space telescopes have always been the most direct tool for human observation of the universe. However, limited by the capability of current optical manufacturing equipment, the difficulty, cycle and cost of fabricating the primary mirror increase significantly as the optical surface aperture increased, and the accuracy requirements of the mirror are also closely related. In order to reduce the machining accuracy requirements, a freeform optical wavefront compensation method was proposed to increase the tolerance on the manufacturing error of the primary mirror. In this paper, we compensated two different large aperture telescope systems, and one of their mirrors were replaced by freeform surfaces represented by 37-term Zernike fringe polynomials in the optical system to correct the system wavefront distortion caused by the machining error of the large-aperture primary mirror. A new algorithm that is based on the principle of equal optical path and ray tracing was adopted here for the construction of freeform surfaces. The design results proved the superiority of the compensation method and the new algorithm of freeform surface. The machining accuracy demand was reduced by more than one order of magnitude, and high-quality imaging of the optical system was realized with the low-precision primary mirror.
Freeform optics have been found in a variety of beam shaping designs. However, they are typically used to form prescribed illumination patterns on a planar surface. In this paper, we will demonstrate a ray mapping based method to design smooth freeform lenses to form complicated illumination distributions on curved surfaces. The ray mapping between the source and target is established by solving an optimal mass transportation problem which is governed by the Monge-Ampére partial differential equation. Then, the freeform lens is constructed by a geometric method based on the optimal ray mapping. Finally, the performance of the lens is verified by Monte Carlo ray tracing simulation in Zemax OpticStudio software. To show the effectiveness of the proposed method, several freeform lenses are designed as examples for a collimated light source to generate different illumination patterns on different curved surfaces. A freeform lens is also fabricated and experimented.
The primary mirror of AIMS solar telescope is heated during the observation of the sun, leading to temperature rise of the primary mirror. The temperature difference between the primary mirror and the surrounding air may cause the seeing effect (mirror seeing), which is one of the key factors influencing the image qualities of the telescope. In this paper, the temperature fields of the primary mirror and its surrounding air are simulated by the CFD software on the conditions of different ambient wind speeds, different observational angels of the primary mirror, and the duration of observation. According to the calculation of temperature fields, the mirror seeing on different conditions are analyzed and the necessity of thermal control of the primary mirror is evaluated. The evaluation of the mirror seeing is very helpful for the design of thermal control of the primary mirror.
The AIMS, a solar telescope with a primary mirror of 1m in diameter, is designed with an off-axis Gregorian optical system and an alt-az mounting structure. The image rotation of the AIMS will be produced both due to alt-az mounting and the movement of plane mirrors system during the monitoring of the sun. Therefore, a derotator is planned to correct and compensate the image rotation to make the terminal instruments of the AIMS work properly. The image rotation in astronomical telescopes consists of the object field rotation and the image field rotations. In this paper, the rotation of the object field for the AIMS is presented and calculated. The image field rotation due to the plane mirrors system with the movement of azimuth axis and altitude axis of the AIMS is theoretically determined by using the ray tracing and vector matrix method. The relationships between the image filed rotation and the variation of the azimuth and altitude of the telescope are discussed. This work may be very helpful to evaluate the deroation methods for the AIMS and will provide an important theoretical support for precision control of the derotator to eliminate the image rotation in real time.
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