Laboratory Frequency Redistribution Function for the Polarized $\Lambda$-Type Three-Term Atom

TL;DR

This paper derives a generalized frequency redistribution function for polarized $Lambda$-type three-term atoms, accounting for atomic polarization and coherence in metastable levels, relevant for modeling polarized line formation in tenuous plasmas.

Contribution

It introduces a generalized redistribution function that extends the $R_{II}$ function to include polarization and coherence effects in metastable levels of $Lambda$-type atoms.

Findings

Provides a theoretical framework for polarized line formation in tenuous plasmas.

Extends the $R_{II}$ redistribution function to polarized, metastable levels.

Applicable to astrophysical plasma diagnostics.

Abstract

We present the frequency redistribution function for the polarized three-term atom of the $\Lambda$-type in the collisionless regime, and we specialize it to the case where both the initial and final terms of the three-state transition are metastable (i.e., with infinitely sharp levels). This redistribution function represents a generalization of the well-known $R_{\rm II}$ function to the case where the lower terms of the transition can be polarized and carry atomic coherence, and it can be applied to the investigation of polarized line formation in tenuous plasmas, where collisional rates may be low enough that anisotropy induced atomic polarization survives even in the case of metastable levels.