Polarized light scattering with Paschen-Back effect, level-crossing of fine structure states and partial frequency redistribution

TL;DR

This paper extends the theoretical framework for polarized light scattering to include partial frequency redistribution effects under arbitrary magnetic fields, focusing on the Paschen-Back regime relevant to solar spectral lines.

Contribution

It generalizes the scattering matrix formalism to account for PRD effects in strong magnetic fields, enabling more accurate modeling of solar spectral line polarization.

Findings

Validated the formalism against benchmarks.

Applied to Li I D lines to predict observable Paschen-Back effects.

Enhanced understanding of magnetic field influences on solar spectra.

Abstract

The quantum interference between the fine structure states of an atom modifies the shapes of the emergent Stokes profiles in the Second Solar Spectrum. This phenomenon has been studied in great detail both in the presence and absence of magnetic fields. By assuming a flat-spectrum for the incident radiation, the signatures of this effect have been explored for arbitrary field strengths. Even though the theory which takes into account the frequency dependence of the incident radiation is well developed, it is restricted to the regime in which the magnetic splitting is much smaller than the fine structure splitting. In the present paper, we carry out a generalization of our scattering matrix formalism including the effects of partial frequency redistribution (PRD) for arbitrary magnetic fields. We test the formalism using available benchmarks for special cases. In particular we apply it to the Li\,{\sc i} 6708\,\AA\ D$_1$ and D$_2$ line system, for which observable effects from the Paschen-Back regime are expected in the Sun's spectrum.