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摘要:
中国1.8 m太阳望远镜(Chinese large solar telescope, CLST)致力于对太阳偏振的高精度及高灵敏度测量。然而其系统本身会引入仪器偏振, 并且在望远镜运行的过程中, 仪器偏振会随其指向的变化而变化。这就降低了系统的测量精度。因此, 需要一个偏振标定单元对其仪器偏振进行标定。为此, 本文对偏振标定的原理和方法进行了研究, 并且给出了针对CLST的偏振标定单元设计方案。
Abstract:It is the main task for the Chinese large solar telescope (CLST) with a 1.8 m aperture to measure the solar polarization with a high accuracy and sensitivity.However, the telescope system itself will introduce instrumental polarization.It also will change constantly with the rotating of the telescope and will reduce the accuracy.Therefore, a calibration unit is necessary to calibrate it.In this paper, we introduced the polarization calibration method and proposed a calibration unit structure.
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Key words:
- solar telescope /
- polarimetry /
- calibration /
- instrumental polarization
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Overview: Practically all solar phenomena are more or less relative to the solar magnetic field. It produces relativelystable structures like sunspots or prominences and is responsible for spectacular dynamic phenomena like flares or coronal mass ejections. However, the generation, amplification and destruction of magnetic fields remain poorly understood. The knowledge of its magnitude and direction is crucial for interpreting measurements of other parameters, and itcan be measured usually by a polarimetry at some special spectral lines, which should be sensitive to the Zeeman effect.To answer what physical mechanisms are responsible for heating the corona, what causes variations of radiative outputin the Sun, and what mechanisms trigger flares and coronal mass ejections and so on, many large aperture solar telescope have been developed (such as VTT, GREGOR, NST) or have being developed (such as DKIST, EST), and theStokes polarimetry is their most important observational device for determining the magnetic field. The Chinese largesolar telescope (CLST) with a 1.8-m aperture is a classic Gregorian configuration telescope with an alt-azimuth mount.It will be the second largest solar telescope in the world for a long time. And it is the main task for the Chinese largesolar telescope (CLST) to measure the solar polarization with a high accuracy and sensitivity. However, as a classic Gregorian configuration telescope with an alt-azimuth mount, the telescope system itself will introduce instrumental polarization. And it also will change constantly with the rotating of the telescope. Therefore a calibration unit which produces light of known polarization states is necessary to measure the Muller matrix of the system and apply the correction numerically on the measured Stokes vector.
In this paper, we introduced the polarization calibration method and proposed a calibration progress. Since the telescope is rotational, symmetric down to M4, the position of the secondary focus F2 is appropriate for a calibration unitbecause the components before it do not contribute to the Muller matrix. F2 is an extremely useful position in CLST. Itshould be used not only for polarimetric purposes but also for internal alignment. Thus the calibration unit becomes amore versatile device. Then we design the structure of CLST calibration unit with two turnplates. The calibration unitoptics equipped on these turnplates will consist of a rotatable linear polarizer, and two rotatable achromatic quarter waveplates which are in use alternatively for visual range or infrared observations. And there are also some other space on theturnplates to realize the internal alignment purposes.
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表 1 CLST系统参数指标
Table 1. The parameters of CLST system
Parameter Value Aperture size of M1/mm Φ1800 Field of view (FOV)/(′) ≥Φ3 Wavelength cover/nm 380~2500 Image space F# F/54.5 Focal length/m ~96 
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表 2 偏振调制方案
Table 2. Polarization modulation program
Number Polarizer angle/(°) λ/4 wave plate angle Stokes 1 0 none [1 1 0 0]T 2 45 none [1 0 1 0]T 3 90 none [1 -1 0 0]T 4 0 45° [1 0 0 1]T
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表 3 偏振标定单元精度要求
Table 3. Accuracy requirement of polarization calibration unit
Parameter Error κ < 0.001 θ1/(°) < 0.05 δ/(°) < 0.1 θ2/(°) < 0.05
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表 4 F2焦点系统参数
Table 4. System parameters in F2
Parameter Value Circular diameter/mm 27 Image scale/(″/mm) 18.93 Focal length/mm 10897 F ratio 6.2 Power density/(W/cm2) 26 Power/W 160
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表 5 驱动电机性能要求
Table 5. Requirements for motor drives
Drive A Drive A1 Drive B Drive B1 Position precision/(°) < 0.05 < 0.05 < 0.05 < 0.05 Position repeatability/(°) < 0.1 < 0.1 < 0.1 < 0.1 Rotation speed/(rpm) < 3 >10 >3 >10
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表 6 转盘各通光孔装置及应用
Table 6. The device and their useful on the rotator
Device Application A1 Rotating polarizer 1 To introduce linear polarization In visible wavelength A2 Rotating polarizer 2 To introduce linear polarization In near infrared wavelength A3 Full FOV A4 Fiber adapter Holder for a fiber A5 Empty For later use A6 Empty For later use B1 λ/4 wave plate 1 To introduce circular polarization In visible wavelength B2 λ/4 wave plate 1 To introduce circular polarization In near infrared wavelength B3 Full FOV B4 Pinhole To align the wave front sensor and so on B5 Resolution target Used for focusing M3 B6 Slanted edge target To measure directly the MTF
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[1] Hofmann A, Rendtel J.Polarimetry with GREGOR[J].Proceedins of SPIE, 2003, 4843:112-121. doi: 10.1117/12.458615
[2] Beck C, Bellot Rubio L R, Kentischer T J, et al.Two-dimensional solar spectropolarimetry with the KIS/IAA Visible Imaging Polarimeter[J].Astronomy & Astrophysics, 2010, 520:A115. http://arxiv.org/abs/1007.1153v2
[3] Von Der Lühe O, Schmidt W, Soltau D, et al.GREGOR:a 1.5 m telescope for solar research[J].Astronomische Nachrichten, 2001, 322(5-6):353-360. doi: 10.1002/(ISSN)1521-3994
[4] Cao W, Ahn K, Goode P R, et al.The new solar telescope in big bear: polarimetry Ⅱ[C]//Proceedings of ASP Conference, 2011: 345-349.
[5] Keil S L, Rimmele T R, Oschmann J, et al.Science goals and development of the advanced technology solar telescope[J].Proceedings of the International Astronomical Union, 2004, 2004(IAUS223):581-588. doi: 10.1017/S1743921304006933
[6] Matthews S A, Collados M, Mathioudakis M, et al.The European solar telescope (EST)[J].Proceedings of SPIE, 2016, 9908:990809. doi: 10.1117/12.2234145
[7] 屈中权, 张霄宇, 陈学昆, 等.太阳光谱望远镜和Stokes光谱测量[J].天文学进展, 2001, 19(2):139-140. doi: 10.3969/j.issn.1000-8349.2001.02.012
Qu Z Q, Zhang X Y, Chen X K, et al.Solar spectroscopy telescope and the stokes spectrometry[J].Progress in Astronomy, 2001, 19(2):139-140. doi: 10.3969/j.issn.1000-8349.2001.02.012
[8] 方成, 黄佑然.南京大学太阳塔及多波段太阳光谱仪[J].天文学报, 1983, 24(3):189-195. doi: 10.15940/j.cnki.0001-5245.1983.03.001
Fang C, Huang Y R.The solar tower telescope of Nanjing university and its multiple solar spectrograph[J].Acta Astronomica Sinica, 1983, 24(3):189-195. doi: 10.15940/j.cnki.0001-5245.1983.03.001
[9] 许方宇, 徐稚, 徐世春, 等.抚仙湖一米新真空太阳望远镜6米近红外光谱仪装调及太阳1.56微米光谱的初步观测结果[J].天文研究与技术, 2014, 11(2):168-175. doi: 10.3969/j.issn.1672-7673.2014.02.012
Xu F Y, Xu Z, Xu S C, et al.Installation/adjustment of a 6m near-infrared spectrograph for the 1m new vacuum solar telescope in the Fuxian-Lake solar-observation station and preliminary observation results of solar spectra around 1.56 μm using the spectrograph[J].Astronomical Research and Technology, 2014, 11(2):168-175. doi: 10.3969/j.issn.1672-7673.2014.02.012
[10] Yuan S.Polarization model for the new vacuum solar telescope[C]//Proceedings of APS Conference, 2014: 297.
[11] Hofmann A.Polarimetry with GREGOR-an ongoing project[J].Sun and Geosphere, 2007, 2(1):9-12. http://adsabs.harvard.edu/abs/2007SunGe...2....9H
[12] Bettonvil F C M, Collados M, Feller A, et al.The polarization optics for the European Solar Telescope (EST)[J].Proceedings of SPIE, 2010, 7735:77356I. http://proceedings.spiedigitallibrary.org/data/Conferences/SPIEP/5979/77356I_1.pdf
[13] Rao C H, Gu N T, Zhu L, et al.1.8-m solar telescope in China:Chinese large solar telescope[J].Journal of Astronomical Telescopes, Instruments, and Systems, 2015, 1(2):024001. doi: 10.1117/1.JATIS.1.2.024001
[14] Azzam R M A, Masetti E, Elminyawi I M, et al.Construction, calibration, and testing of a four‐detector photopolarimeter[J].Review of Scientific Instruments, 1988, 59(1):84-88. doi: 10.1063/1.1139971
[15] Krishnan S.Calibration, properties, and applications of the division-of-amplitude photopolarimeter at 632.8 and 1523 nm[J].Journal of the Optical Society of America A, 1992, 9(9):1615-1622. doi: 10.1364/JOSAA.9.001615
[16] Snik F.Calibration strategies for instrumental polarization at the 10-5 level[J].Proceedings of SPIE, 2006, 6269:62695P. doi: 10.1117/12.671425
[17] 侯俊峰.偏振分析器的高精度偏振定标方法研究及其应用[D].北京: 中国科学院大学, 2013.
Hou J F.Studies and applications of polarimeter's polarization calibration with high precision[D].Beijing: University of Chinese Academy of Sciences, 2013.
[18] Almeida J S, Pillet V M.Instrumental polarization in the focal plane of telescopes[J].Astronomy and Astrophysics, 1992, 260(1-2):543-555. http://adsabs.harvard.edu/abs/1992A&A...260..543S
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