太阳散射偏振研究进展

Progressed in Studying Scattering Polarization in Solar Atmosphere

太阳磁场的诊断对研究太阳物理有着重要的意义。近几十年,许多科学家利用汉勒效应(Hanle effect)进行诊断弱磁场的研究。而利用汉勒效应诊断弱磁场,需要对偏振的产生机制有一个完整的理解。直到近年来,随着技术的发展,对偏振的测量精度达到10^(-5)的ZIMPOL(Zurich Imaging Polarimeter)获得以斯托克斯参量Q/I为表征的第二太阳光谱(second solar spectrum),展现丰富的散射偏振特征,促进了偏振研究的蓬勃发展。通过对第二太阳光谱的研究,使我们对偏振产生机制理解得更为透彻,从而使利用汉勒效应诊断弱磁场逐渐成为可能。主要介绍了用量子电动力学为基础的密度矩阵来研究偏振光谱产生的物理过程,并简要介绍了近年有关在第二太阳光谱和汉勒效应研究的一些进展。

The magnetic field plays a very important role in solar atmosphere. The diag-nostic of the strong magnetic field is usually based on Zeeman effect. When the magnetic field is so weak that Zeeman effect becomes less e？cient, Hanle effect can provide another diagnostic tool to diagnose the weak magnetic field. However this needs a complete un-derstanding of the polarization mechanisms. A series of International Solar Polarization Workshops （SPWs） which focus on probing the magnetic field have been held every three years since the first one in St.Petersberg, Russia, in 1995. As the high polarimetric precision 〈br〉 technology was applied by the ZIMPOL （Zurich Imaging Polarimeter）, the so-called Second Solar Spectrum was observed and it shows a great amount of rich and complicated struc-tures of the linear polarization profiles. The linear polarized spectrum is a playground for Hanle effect application in solar atmosphere. Through the efforts by a lot of scientists, the theories to treat the Hanle effect were developed, like the statistical equilibrium equations and radiative transfer equation in form of the density matrix. These theories have made great successes and solved many problems in the polarization profile formation, but they still face some di？culties. Here we review the basic theories in the scattering polarization to deal with the Second Solar Spectrum and Hanle effect, and describe the progressing in this area.