Interaction of a Poincaré beam with optically polarized atoms in the presence of constant magnetic field

Abstract: Recent studies have highlighted the frequent applications of structured light modes in optically pumped atomic magnetometers. In this work, we theoretically explore how a Poincar\'e beam probes an optically polarized atomic medium. Specifically, we consider atoms polarized by a plane wave with linear polarization, immersed in a constant external magnetic field. We analyze how the polarization of the pump and probe light fields, along with the external magnetic field, impact the absorption profile. To this end, we employ a density matrix approach based on the Liouville-von Neumann equation. Our results reveal that the absorption profile exhibits an asymmetric pattern that depends on the magnetic field strength and the mutual orientation of the pump and probe light propagation directions relative to the quantization axis. For illustration, we assume the incoming radiation drives an electric dipole transition, $5s \, ^2S_{1/2}$ ($F=1$) $\rightarrow$ $5p \, ^2P_{3/2}$ ($F=0$), in rubidium atoms subjected to a magnetic field. These findings may aid in designing future experiments on optically pumped atomic magnetometers utilizing structured light modes.