中国科学院云南天文台机构知识库

磁场测量是太阳科学观测中最重要的一部分,围绕磁场展开的相关研究是太阳物理的研究热点.磁像仪是一种可以进行高分辨磁场观测的精密测量器件,在地基和空间太阳观测中得到了广泛的应用.窄带可调谐滤光器是磁像仪获得窄带光的核心光学部件,其特性会对磁像仪的性能产生影响.滤光器分为两大类,具体可包括4种结构,不同结构具有不同的性能特征,可根据磁像仪的需求进行选择.本文调研了国内外著名地基、球载、空间太阳磁场望远镜,总结了太阳磁像仪中常用的各种窄带可调谐滤光系统的实现方式,滤光器的结构、原理、轮廓特性以及在磁像仪中的应用场景,归纳了不同太阳磁像仪滤光系统的设计特点和关键技术,以期为未来太阳磁像仪滤光系统的研制提供参考. 

Solar magnetic field observations achieve a precise understanding of the solar activity. Imaging spectropolarimetry obtains the magnetic field strength for the entire field of view simultaneously and spectral samples sequentially. By employing highresolution reconstruction methods, ground-based solar imaging spectropolarimeters are suitable for magnetic field measurements with a high spatial and temporal resolution. The space-borne solar imaging spectropolarimeter has a compact optical path, stable performance, and convenient data processing. Furthermore, it can be used for deep space exploration. Narrowband tunable filters are the primary spectroscopic components of imaging spectropolarimeters for obtaining narrowband light, with various structural forms for different application scenarios from ground to space. Tunable narrowband filters are classified into two categories according to different principles: The Fabry-Perot filter (F-P filter) and the polarization interference filter. The Fabry-Perot filter is divided into two types based on wavelength adjustment methods: Air cavity and lithium niobate. Polarization interference filters are divided into Lyot filters and solid Michelson interferometers according to different beam-splitting structures. Magnetic field measurement using solar imaging spectropolarimetry is a high-precision measurement with strong noise and weak signal. The performance of the narrowband tunable filter determines the accuracy of the spectral transmittance curve, and the filter instability will increase the noise and affect the accuracy of the magnetic field intensity. The narrowband tunable filter, as the most complex component in the optical path of imaging spectropolarimeters, must solve different technical problems in various application scenarios, and the key technology directly affects whether the magnetic image can be obtained. Therefore, how to design the filter system based on different application scenarios is a problem that must be solved for imaging spectropolarimetry to achieve high-precision observation. This paper investigates famous solar spectropolarimeters of ground-based, balloon-borne, and space-borne. Two or three types of filters are used to meet the requirements of different application scenarios. Air-gap F-P filters are characterized by high transmittance, high spectral resolution, and low sidelobe, and they can be applied in the near-infrared band. Its most remarkable advantage is that larger apertures can be manufactured as production technology advances. The stability of this filter is the toughest problem. The filter relies on a calibrated optical path to achieve accurate adjustment even when used on the Coude platform. As a result, the F-P filter requires a relatively stable platform with a large space. It could have a sizable aperture, making it suitable for the next generation of large-aperture ground-based telescopes with a Coude platform. LiNbO3 F-P filter, solid Michelson interferometer, and Lyot filter have the advantage of stable performance. They are suitable for space-borne, balloon-borne, and other systems with poor mechanical stability. The Lyot filter has excellent stability. Temperature is the only factor that needs to be considered. The surface precision requirements of the Lyot filter are low, whereas those of the solid Michelson and LiNbO3 F-P filters are high. The LiNbO3 F-P filter needs to consider the influence of high voltage. The Lyot filter is made of natural crystal, which makes achieving a large aperture difficult. The artificial glass or crystal used in the solid Michelson interferometer and LiNbO3 F-P filter allows for a larger aperture but places high demands on processing technology. One of China’s 8 m CGST’s scientific goals is to achieve high-precision and high-resolution vector magnetic field measurements in NIR, which requires further development of a large-aperture air-gap F-P filter in NIR. China has developed several 1 m aperture solar telescopes in recent years. The 2 m RST of Yunnan Observatory will be completed soon. RST’s imaging spectropolarimeter is located in the main focus of the telescope, which requires stable filter performance, and the Lyot filter meets the demand. China’s next-generation space solar magnetometer can succeed in choosing the Lyot filter. If the spectral resolution is required, a combination of tunable wide-field solid Michelson interferometer and Lyot filter can be used. LiNbO3 F-P filters are also a new research area. It is foreseen that China will have multiple solar telescopes to achieve high-resolution vector magnetic field measurements in multiple bands and make contributions to solar physics.