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.
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.
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.
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.
In this paper, a colorful schlieren system without any protecting windows was introduced which results in that the 1.2m primary mirror would directly be confronted with the pressure and temperature variation from the wind tunnel test. To achieve a good schlieren image under the wind tunnel test working condition of a wide temperature fluctuation range (-10° to 50°) as well as a pressure (2kPa), a new flexible support method of the primary mirror was strategically designed. A finite element model of the primary mirror combined with its supporting structures was built up to approach the surface figure of the primary mirror under the complex working conditions as gravity, temperature variation, and pressure. The schlieren images due to the change of the primary mirror surface figure were simulated by Light-tools software. It was found that the temperature changing and pressure would lead to the variation of the surface figure of the primary mirror surface figure and therefore, results in the changing of the quality of simulated schlieren images.
Schlieren photography is a visual process to display the flow of fluids of varying density. It is widely used in wind tunnel tests to photograph the flow of air around objects. To achieve schlieren images with high sensitivity and high resolution, and satisfy the requirements of the large-scale wind tunnel tests, it is urgent to develop schlieren photographers with large aperture primary mirrors. However, the application of large aperture primary mirrors may bring many challenges in the design of the schlieren system. First, the surface figure of large aperture primary mirrors is difficult to control so that the support structure may need more strategical design. Second, because the schlieren system works under some severe environments of the wind tunnel test including the air disturbance, wind-induced ground vibration and high ambient pressure, it has to withstand serious instability risks to ensure a good schlieren image quality. In this work, the current status of the development in the large aperture schlieren systems is reviewed. Several advanced methods, for example, active damping control technique, focal spot monitoring technique, 18-points whilffletree support technique, etc.., are introduced to deal with the challenges of the large aperture schlieren system. This work aims at improving the technical development of large aperture schlieren photographer, which may contribute to the acquisition of the high sensitive and high resolution schlieren images and the improvement of the testing capability in wind tunnel experiments.
Diffractive telescopes are ideal to space-based lidar receivers, because of their advantages of mass and surface shape tolerances. To develop diffractive optical systems, the aberration properties and high order diffraction of diffractive lenses were discussed. The aberration properties are suitable for lidar receivers. High order diffraction is helpful to improve diffractive lens fabrication and decrease system length. And it can be realized by modifying the surface figures of a diffractive lens, mainly the ring widths and depth. A 1-meter aperture diffractive telescope design with simple structure was given, providing spot diameters less than 45μm over the whole field of view.
Diffraction image technology is an updated technology. It has more potential for developing the larger aperture and lightweight telescope than the conventional refractive and reflective optics. In order to develop a large aperture diffractive telescope, the key is to solve the problem of large aperture lens stitching. Different stitching patterns have different effects on the image quality. However, the stitching pattern for diffractive telescope is different from the conventional refractive and reflective telescope. This paper, for the first time, studies the theory of stitching pattern for diffractive telescope. On the basis of theoretical analysis, a long-wavelength infrared diffractive telescope of segmented-lens is designed and for the first time, good results through stitching experiments have been achieved. According to theoretical analysis and experiment verification, the paper gives the best stitching pattern on diffractive telescope.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.