Spin-orbit coupling of optical vector vortices in coherently prepared media

TL;DR

This paper studies how optical vector vortices interact with a coherently prepared atomic medium, revealing how orbital angular momentum is mapped onto atomic coherence, leading to complex polarization and intensity patterns due to spin-orbit coupling.

Contribution

It demonstrates the analytical propagation of vortex pairs in a three-level medium and uncovers the topological mapping of OAM onto atomic coherence causing polarization evolution.

Findings

The medium inherits the vortex pair topology, creating azimuthal transparency structures.

OAM is mapped onto atomic coherence, inducing optical anisotropy and spin-orbit coupling.

Polarization states evolve from circular to linear depending on initial conditions.

Abstract

We investigate the propagation of an optical vector vortex weakly interacting with a coherently prepared atomic medium (phaseonium) in a three-level $\Lambda$ configuration. The vector beam consists of vortex pulse pairs with right- and left-circular polarizations, corresponding to opposite spin angular momentum (SAM), and carrying opposite orbital angular momentum (OAM) charges $\pm l$. We show that during the propagation of the vortex pairs, analytically obtained in the linear regime, the medium inherits the topology of the vortex pair, mapping the OAM onto a spatially structured atomic coherence. This mapping produces $2|l|-$fold azimuthal transparency structures that reshape the beam intensity from a ring into a petal-like pattern. The OAM-structured atomic coherence induces a corresponding optical anisotropy within the medium, which feeds back into the propagating vector beam, resulting in optical spin-orbit coupling manifested as SAM exchange, rotation, and evolution of polarization textures. Depending on the initial ground-state population of the phaseonium, the polarization state evolves between left-circular, linear, and right-circular polarizations.