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The influence of the telescope optical structures on adaptive optics compensation
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Abstract
Abstract: Adaptive optics has played an important role in high resolution telescope. The low order aberrations of the telescope can be completely compensated by adaptive optics, but it causes the loss of the compensation stroke of the deformable mirror. The middle and high order aberrations after compensating of the deformable mirror have some residual aberration, so we need control the residual aberration to ensure high resolution imaging quality, especially the high order residual aberration that can't be compensated, which should be strictly controlled in the beginning of the design of the telescope system. This paper analyzes the structure of primary mirror of the telescope optical system, secondary mirror block, secondary mirror support bars block, the primary mirror and secondary mirror alignment, and the static and quasi-static aberration of the optical machining. The influence of these factors on the adaptive optics compensation is analyzed, and the requirements of the aberration control are given.-
Keywords:
- adaptive optics /
- optical structure /
- high aberration /
- secondary mirror support bars
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References
[1] 姜文汉.自适应光学技术[J].自然杂志, 2006, 28(1): 7–13. Jiang Wenhan. Adaptive optical technology[J]. Chinese Journal of Nature 2006, 28(1): 7–13. [2] Thompson L. Adaptive optics for astronomical telescopes, by John W. Hardy adaptive optics in astronomy, by Fran ois Roddier[J]. Physics Today 2000, 53(4): 69. doi: 10.1063/1.2405463 [3] Schipani P, Noethe L, Magrin D, et al. Active optics system of the VLT survey telescope[J]. Applied Optics 2016, 55(7): 1573–1583. doi: 10.1364/AO.55.001573 [4] Schipani P, D'Orsi S, Ferragina L, et al. Active optics primary mirror support system for the 2.6 m VST telescope[J]. Applied Optics 2010, 49(8): 1234–1241. doi: 10.1364/AO.49.001234 [5] 王金, 鲜浩, 王胜千, 等.拼接式望远镜子镜间平移、倾斜误差及子镜间隙对成像质量的影响[J].光电工程, 2014, 41(10): 55–62. doi: 10.3969/j.issn.1003-501X.2014.10.010 Wang Jin, Xian Hao, Wang Shengqian, et al. Effects of piston, tip-tilt and gap errors on image quality of the segmented telescope[J]. Opto-Electronic Engineering 2014, 41(10): 55–62. doi: 10.3969/j.issn.1003-501X.2014.10.010 [6] 廖周, 邱琪, 张雨东.大口径拼接望远镜成像系统的远场特性[J].光电工程, 2015, 42(2): 1–8. Liao Zhou, Qiu Qi, Zhang Yudong. The far-field characteristics for large aperture segmented telescope system[J].Opto-Electronic Engineering 2015, 42(2): 1–8. [7] 陆长明, 饶长辉, 黄惠明, 等.天文学自适应光学成像望远镜的模拟[J].光电工程, 2006, 33(1): 20–23. Lu Changming, Rao Changhui, Huang Huiming, et al. Simulation of an astronomical adaptive optics imaging telescope[J]. Opto-Electronic Engineering 2006, 33(1): 20–23. [8] Baiocchi D. Design and control of lightweight, active space mirror[D]. Arizona: The University of Arizona, 2004: 22–32. [9] Yellowhair J E. Advanced technologies for fabrication and testing of large flat mirrors[D]. Arizona: The University of Arizona, 2007: 27–34. [10] Martin H M, Davison W B, DeRigne S T, et al. Active supports and force optimization for a 3.5 m honeycomb sandwich mirror[J]. Proceedings of SPIE 1994, 2199: 251–262. doi: 10.1117/12.176194 [11] Gray P M, Hill J M, Davison W B, et al. Support of large borosilicate honeycomb mirrors[J]. Proceedings of SPIE 1994, 2199: 691–702. -
Overview
In the process of high resolution imaging of celestial objects, adaptive optics system plays an important rolein the compensation of atmospheric turbulence and the improvement of imaging quality. However, the adaptive opticssystem is in a certain condition between two extreme situations, which are fully uncompensated and fully compensated, and belongs to partially compensated optical system. Adaptive optics can achieve almost full compensation forlow order aberrations, but the compensation ability for high order aberration is limited. The low order aberrations ofthe telescope can be completely compensated by adaptive optics, but it causes the loss of the compensation stroke ofthe deformable mirror. The middle and high order aberrations after compensating of the deformable mirror, which areproduced mainly by telescope structures, alignment and processing, have some residual aberration. This residual aberrations result in severe degradation of imaging quality of the telescope. So we need control the residual aberration toensure high resolution imaging quality, especially the high order residual aberration that can’t be compensated, whichshould be strictly controlled in the beginning of the design of the telescope system.
We analyze the influence of the telescope optical structures on adaptive optics compensation, mainly for the 4 metertelescope. First of all, the simulation analysis of adaptive optics system layout of the 4 meter telescope is presented, inorder to analyze the residual aberrations with compensated by 4 meter adaptive optical system. The specific analysis ofthe optical structures on the layout correction capability of our adaptive optical system contains the following content:the structure of primary mirror of the telescope optical system, mainly the honeycomb structure, the primary mirrorsupport structure, the primary mirror temperature deformation, secondary mirror block, secondary mirror supportbars block, and the static and quasi-static aberration of the optical processing. The influence of these factors on theadaptive optics compensation is analyzed, so that the requirements of the aberrations control are given.
Low order aberrations such as defocus and astigmatism caused by primary and secondary mirror alignment, primary mirror support, and primary mirror thermal deformation, can be completely corrected by adjusting the secondary mirror or using a single deformable mirror which has large compensation stroke. High order aberrations out theability of adaptive optics compensation, such as the aberrations caused by honeycomb structure of primary mirror, canbe compensated by data processing. In the process of telescope design and processing, the factors that lead to a largenumber of high order aberrations should be strictly controlled, and high control requirements are put forward.
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Figure 1.
Deformable mirror layout and Hartmann wavefront sensor layout.
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Figure 2.
Correction capability analysis.
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Figure 3.
Structure and surface wavefront of honeycomb mirror.
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Figure 4.
Compensation effect in surface error of 1.8 m honeycomb mirror by deformable mirror actuator spacing changing.
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Figure 5.
Surface wavefront of primary mirror pointing horizontal direction and the residual surface wavefront by deformable mirror compensated.
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Figure 6.
Surface wavefront of the temperature distortion and the residual surface wavefront by deformable mirror compensated. (a) Original surface. (b) The surface after removing defocus. (c) The residual surface by deformable mirror compensated.
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Figure 7.
Secondary mirror block of telescope. (a) Front view. (b) Top view.
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Figure 8.
(a) Deformable mirror layout of the 847 actuators. (b) Hartmann wavefront sensor layout.
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Figure 9.
Compensation capacity of deformable mirror by secondary mirror block changing.
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Figure 10.
Split wavefront of adding the secondary mirror support bars block. (a) Aberration source signal. (b) Aberration source signal. (c) DM's fitting surface. (d) Remainder error.
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Figure 11.
The effect of compensation by deformable mirror with the size (a) and rotation of the secondary mirror bars changing (b).
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Figure 12.
The statistical distribution of optical processing static error of planar mirror.
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Figure 13.
The statistical distribution of optical processing static error of aspheric mirror.
