Accurate infrared magnetic system (AIMS) is a ground-based solar telescope with the effective aperture of 1 m. The system has complex optical path and contains multiple aspherical mirrors. Since some mirrors are anisotropic in space, parallel light undergoes complex spatial reflection after passing through the optical pupil. It is also required that part of the optical axis coincides with the mechanical rotation axis. The system is difficult to align. This article proposes two innovative alignment methods. First, a modularized alignment method is presented. Each module is individually assembled with optical reference reserved. System integration can be completed through optical reference of each module. Second, computer-aided alignment technology is adopted to achieve perfect wavefront. By perturbing the secondary mirror (M2), the influence of M2 position on the wavefront is measured and the mathematical relationship is obtained. Based on the measured wavefront data, the least squares method is used to calculate the M2 alignment and multiple adjustments have been made to M2. The final system wavefront has reached RMS=0.12 λ@632.8 nm. Through observations of stars and sunspots, it has been demonstrated that the optical system has good wavefront quality. The observed sunspot is clear with the penumbral and umbra discernible. The proposed method has been verified and provides an effective alignment solution for complex off-axis telescope with large aperture.
This paper investigates a method for measuring and calibrating the mirror attitude, tilt monitoring system, and compensation lens in a diffraction camera. Firstly, a measurement network is established by installing a reference prism and a theodolite on the load-bearing plate, enabling the overall measurement of the position of the mirror relative to the camera. Then, by changing the attitude of the mirror and recording the changes in the detector point coordinates, the relationship between the direction angle of the mirror and the detector point coordinates is calculated. Then, by adjusting the compensation lens in its local coordinate system, the relationship between the compensation lens and the detector point coordinates is obtained. Finally, by substituting the above matrix into the conversion matrix formula, the conversion matrix between the direction angle of the secondary mirror and the compensation lens translation is obtained, thereby completing the calibration of the attitude. This method can directly drive the compensation lens according to the change in the position of the mirror, ensuring the imaging quality of the camera.
A five-mirror optical derotator system is used in the Accurate Infrared Magnetic System solar telescope by virtue of its polarization-free and superior real-time performance. The derotator system can compensate image rotation during tracking observation. The system consists of five flat mirrors with their normal vectors noncoplanar. Due to the complicated spatial positions of mirrors, it is challenging to align the system with high accuracy. We analyze parallelism and concentricity characteristic of derotator system by matrix transformation and propose a compensation alignment method from multivariables perturbation simulation. This method reduces degrees of freedom for alignment from 10 to 4, which greatly simplifies the installation and adjustment process. Based on the above simulation, the alignment experiment has been conducted successfully with the parallelism and concentricity meeting the requirements. Through theoretical analysis and experimental verification, the proposed method is reasonable and provides an efficient alignment solution for this kind of five-mirror optical derotator system.
In this paper, the assembly and rectification method of the new optical system is studied. According to the characteristics and difficulties of the diffraction camera, the assembly and rectification scheme is formulated. Firstly, the space angle of the mirror is determined by the spatial attitude measurement and the reference conversion matrix method. The coaxial adjustment and combined detection and adjustment of each transmission lens group are completed by the self alignment method. The method of sensitivity matrix iterative fine adjustment based on aberration is applied in the whole machine assembly and adjustment process. Finally, the high-precision assembly and detection of the complex offset axis infrared diffraction camera were completed, and the wave aberration on the axis reached 0.119λ@3.39μm. The MTF reached 0.13@33lp/mm, meeting the design requirements. This method provides engineering experience and reference for similar camera assembly and adjustment process methods.
In the field of the active wavefront correction for off-axis telescopes, the sensitivity matrix and damped least squares method are widely employed to calculate the misalignment. Improper selection of the damping coefficient will lead to bad wavefront correction results. Moreover, the calculated misalignment is referenced on the optical coordinate system, which cannot be directly applied as the control quantity. The article has two innovative points to solve these problems. First, an adaptive damping least squares method is proposed. The method considers the mirror surface error, uses Python + Zemax cosimulation to perform closed-loop reverse verification, and selects the optimal damping coefficient. Simulation is carried out for verification. Second, the article deduces the mathematical relationship between the calculated misalignment and the mechanism control quantity. Based on the above research, the wavefront active correction experiment has been completed. The optical component is actively adjusted with the wavefront quickly converging to RMS = 0 . 055λ @ 632 . 8 nm. The results verify the correctness of the proposed method.
Coaxial optical system has a symmetry of revolution. Alignment for this kind of optical system is easy. The desired image quality can be rapidly converged. As for off-axis optical system, traditional optical alignment method can not be used due to the loss of rotational symmetry. Low initial position accuracy makes installation and adjustment more difficult than usual. In this paper, we aim to solve the alignment problem for off-axis optical system with the help of machine learning and its powerful numerical fitting ability. We carried out our research on alignment method for an Gregorian off-axis system. The location of primary mirror is fixed as the optical reference. Alignment process is to adjust posture of secondary mirror to acquire ideal image quality. We use Zemax and Python co-simulation technology to get simulated data. Then multi-layer artificial neural network is utilized to fit the mathematical relationship between misalignments and Zernike coefficients. Given the coefficients, the misalignments can be calculated by the neural network. Finally we conduct alignment experiment to verify the proposed method. The result has proved that this method is a fast and efficient alignment solution for the off-axis optical systems.
Off-axis refractive system with the noticeable advantages such as high resolution, large view field and central obscuration removed, has been one of the powerful systems for space astronomical telescopes in recent years. However, misalignment errors and surface error of mirrors are significant especially in the alignment progress of off-axis reflective telescope with large aperture. Computer aided assembling (CAA) jointly provide a robust misalignment correction method to ensure the accurate alignment of telescope. In this paper, system aberration of misalignment coaxial system with two mirrors is analyzed in detail, moreover, the off-axis system is studied further, especially in the off-axis Gregorian system. And the feasibility of correction values solution about off-axis refractive system is discussed. Both the simulation and experiment results demonstrate the feasibility of the proposed alignment method and high accuracy has been achieved. In the testing off-axis Gregorian system, the primary mirror is paraboloid with 1200 mm diameter, 210 mm off-axis distance, and the second mirror is ellipsoid with off-axis distance 129.0 mm, focal length 425 mm and 2125 mm, respectively. For the testing off-axis Gregorian system, the RMS value of primary mirror and second mirror are 0.021 λ and 0.027 λ (λ = 0.6328 nm), and the testing optimization result of system wavefront aberration with RMS value is better than 0.058 λ is achieved. The reverse optimization method testing can achieve high-accuracy measurement ability, which provides efficient and flexible way for the off axis refractive system from various types of elements with complex surfaces.
Large-Aperture Optical Centering Machinery Turning technology has been widely used in precision optical machine assembly. The main principle is to make optical axis and machine axis coincide by maintaining the collimation image and structural end face unchanged when rotating. Structural parts are fabricated precisely after than. This process requires good verticality between the end face of the optical element and its optical axis. A specific method is required to calculate the verticality of the end face and the optical axis. This paper proposed a method based on self-collimated image deviation control and least squares fitting. Combining with an example, numerical calculation is carried out with error analysis. Finally the verticality is 21um which provides reliable data guarantee for the selection of the reference during optical centering fabricating processing.
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