Scattering polarization of hydrogen lines from electric-induced atomic alignment

TL;DR

This paper investigates how electric fields can induce atomic alignment in hydrogen atoms exposed to unpolarized radiation, affecting scattering polarization, which is not possible with magnetic fields or simplified models.

Contribution

It demonstrates that electric fields can induce atomic alignment in hydrogen, a phenomenon absent in two-term models or with Boltzmann-distributed populations.

Findings

Electric fields induce atomic alignment in hydrogen levels.

Alignment occurs even without anisotropic radiation or magnetic fields.

Two-term models and Boltzmann populations do not exhibit this alignment.

Abstract

We consider a gas of hydrogen atoms illuminated by a broadband, unpolarized radiation with zero anisotropy. In the absence of external fields, the atomic J-levels are thus isotropically populated. While this condition persists in the presence of a magnetic field, we show instead that electric fields can induce the alignment of those levels. We also show that this electric alignment cannot occur in a two-term model of hydrogen (e.g., if only the Ly-alpha transition is excited), or if the level populations are distributed according to Boltzmann's law.