Influence Of Magnetic Fields On Level Populations Of Atom And Design Of Solar Polarimeter Of Yunnan 1m Solar Telescope

Magnetic field's research is indispensable to solar physics and even to astrophysics. However, the research of solar magnetic field is more prominent. After all the sun is the nearest distance star from us, and it is also the only star carefully studied by us. As the active regions have strong magnetic fields, sunspot is the obvious embodiment where magnetic field is present in the solar atmosphere. At the same time, it also is a huge magnetic field lab. On the one hand, the research of sunspot makes us learning more properties of magnetic field. On the other hand, it also helps the development of the other's physical subjects.This paper is divided into two parts. In the first part, we present the influence of magnetic fields on the energy level populations of atoms by analyzing the Solar Stokes profiles of FeI6302.5A forming in the solar magnetized atmosphere, with the aid of a departure factor defined to evaluate the deviation from the normal Boltzmann distribution without a magnetic field. This factor is directly related to the ratio of line source function to the continuum one. The relationship between the departure and the magnetic field reveals an effect that the magnetic field induces an exponential increase of the level population of the lower level of FeI6302.5 A(geff = 2.5) with the field strength. This indicates that the magnetic field can cause the redistribution of populations of those levels whose Lande factors are non-zero. Therefore, this effect should be included in the calculation of the statistical equilibrium. Otherwise, an experiment utilizing the Hg5461A line in the laboratory on the earth is carried out to reveal that the exponential relation is independent of variations of temperature, and the excitation is completely magneto-induced. Finally, the exponential relation is explained by taking account of the magnetic energy in the Boltzmann distribution.In the second part, we outline the design of the polarimeter to be mounted in the 1m YunNan Solar Telescope (YNST). It has been shown that the achromatism of the design is satisfactory for the highly accurate measurement of the Solar Stokes spectra of the four selected lines. And this promises the realization of the scientific goals that the magnetic fields in both chromosphere and photosphere can be measured si-...