Polarized scattering of light for arbitrary magnetic fields with level-crossings from the combination of hyperfine and fine structure splittings

TL;DR

This paper develops a formalism to analyze polarized light scattering in atoms with hyperfine and fine structure under arbitrary magnetic fields, revealing complex polarization effects relevant to solar spectral diagnostics.

Contribution

It introduces a new theoretical approach to model polarized scattering with hyperfine and fine structure in arbitrary magnetic fields, including level-crossings in the Paschen--Back regime.

Findings

Identifies polarization signatures from hyperfine and fine structure interference.

Demonstrates effects of level-crossings in the Paschen--Back regime.

Provides a framework applicable to solar spectral line analysis.

Abstract

Interference between magnetic substates of the hyperfine structure states belonging to different fine structure states of the same term influences the polarization for some of the diagnostically important lines of the Sun's spectrum, like the sodium and lithium doublets. The polarization signatures of this combined interference contain information on the properties of the solar magnetic fields. Motivated by this, in the present paper, we study the problem of polarized scattering on a two-term atom with hyperfine structure by accounting for the partial redistribution in the photon frequencies arising due to the Doppler motions of the atoms. We consider the scattering atoms to be under the influence of a magnetic field of arbitrary strength and develop a formalism based on the Kramers--Heisenberg approach to calculate the scattering cross section for this process. We explore the rich polarization effects that arise from various level-crossings in the Paschen--Back regime in a single scattering case using the lithium atomic system as a concrete example that is relevant to the Sun.