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NVST主镜封窗偏振特性测量方法研究
Alternative TitleResearch about Polarization Measurement of Primary Window for New Vacuum Solar Telescope
刘维维
Subtype硕士
Thesis Advisor李银柱 ; 金振宇
2015-07-01
Degree Grantor中国科学院研究生院
Place of Conferral北京
Degree Discipline天文技术与方法
Keyword物理光学 太阳望远镜 仪器偏振 偏振模拟 应力双折射
Abstract一米红外真空太阳望远镜,简称NVST(New Vacuum Solar Telescope),是我国目前最大的地基太阳观测设备,其主要科学目标是获得太阳中低层大气的高分辨磁图。在太阳磁场获得过程中,望远镜自身的仪器偏振会很大程度上影响到观测的精度。对于NVST,其光路结构设计使得封窗玻璃成为主要的仪器偏振来源。为了实现高精度高效率的太阳磁场观测,必须要预测和改正封窗玻璃的偏振影响。为了预测封窗玻璃的偏振效应,本文首先建立了NVST的仪器偏振模型,用以说明封窗玻璃在磁场测量过程中对测量精度的重要影响。然后,通过分别模拟温度和应力对真空封窗的双折射影响,得到:由于温度在封窗上下表面散热方式不同,导致主要温度梯度方向与光轴平行,这使得温度引起的热膨胀形变的方向平行于光轴,同时,膨胀引起的形变总体上比真空压力形变小一个量级。故在分析中,忽略了温度对封窗玻璃的偏振贡献。真空压力和重力载荷引起的双折射影响主要造成了偏振信号Q U、Q V,以及U V之间的串扰,QU之间的串扰量级在10-5左右,QV串扰量级在10-4左右;串扰主要表现为UV串扰,最大为1.28×10-2,最小为0.43×10-2。总的串扰强度随着望远镜指向高度降低而增大。经过数学近似,可把封窗玻璃等效于一块旋转延迟片。在波长532.24nm处,其最大旋转角度为1.1225°,最大延迟角度为0.7346°。最后,通过比较望远镜仪器偏振实的测方法,结合模拟,设计了一套合理的实测装置,分析了测量中的误差。
Other AbstractAt present, one-meter infrared solar telescope (also called New Vacuum Solar Telescope, NVST for short) is the biggest solar telescope in China. Its main scientific goal is to get high-resolution vector magnetic field of the lower atmosphere for solar. In the process of magnetic field measuring, the telescope instrumental polarization will largely affect the accuracy of the measurement. For NVST, the vacuum window is one of the main source of instrumental polarization. To predict the polarization effect of vacuum window, this paper introduces NVST instrumental polarization model and illustrates the great influence of vacuum window. Then, due to the simulation results of the temperature and strain birefringence effect on the vacuum, it shows that because of the different temperatures of the upper and lower surfaces, the main temperature gradient of window is parallel to the optical axis, and the deformation generally is an order of magnitude smaller than the vacuum stress. So, its contribution to the instrument polarization can be ignored; Vacuum stress and gravity mainly causes the signal crosstalk between Q and U, Q and V, U and V, the magnitude of Q and U crosstalk is 10-5, and the magnitude of Q and V crosstalk is around 10-4; and the primary instrumental polarization crosstalk comes from strain is between U and V, the maximum of the crosstalk is 1.28×10-2, and minimum is 0.43×10-2. And the crosstalk increases along with the decrease of the telescope altitude. By a reasonable approximating, the polarization property of vacuum window is equivalent to a rotated retarder. At 532.24 nm wavelength, the maximum rotation angle change of the fast optical axis from its original direction is 1.1225 °, and maximum delay angle is 0.7346 °. Finally after comparing different telescope instrument polarization measurements, a reasonable plan of measurement has been built.
Subject Area天文学
Language中文
Document Type学位论文
Identifierhttp://ir.ynao.ac.cn/handle/114a53/9456
Collection抚仙湖太阳观测站
Affiliation中国科学院云南天文台
Recommended Citation
GB/T 7714
刘维维. NVST主镜封窗偏振特性测量方法研究[D]. 北京. 中国科学院研究生院,2015.
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