Amplification and storage of light carrying orbital angular momentum via magnetically assisted gain in cold atoms

Abstract

We report on the amplification and the storage of a light vortex beam carrying orbital angular momentum in an ensemble of cold cesium atoms in the presence of an external transverse magnetic field. This magnetically assisted optical gain was previously reported in a recent publication and originates from the manipulation of the induced dark state by the external magnetic field. Single pass optical gain exceeding $100\%$ was measured for beams with different topological charges. Furthermore, we also demonstrate the storage and retrieval of the vortex beams, showing that the amplification and the storage processes preserve the coherent nature of the optical vortex. A simple theoretical model based on density matrix numeric calculation and which accounts for the presence of the external magnetic field was developed and present qualitative agreement with the observed results. Owing to the recent proposal of using light carrying orbital angular momentum for efficient data transmission systems, we believe our results could find application in communications protocols involving distant nodes.

Measurement of steep dispersion associated with magnetically assisted gain in Zeeman degenerate two-level system of cold atoms

“…Moreover, it allows the use of magnetic fields as another external control parameter, which can lead to the observation of new phenomena, as for instance, the magnetically assisted optical gain recently observed in cold cesium atoms [7]. This new gain mechanism was recently used to demonstrate laser oscillation [8] and the amplification and storage of structured light [9]. This gain mechanism can be qualitatively understood as resulting from the modification of the dark-state, created by two orthogonally polarized light beams, induced by a transverse magnetic [7], which transfer population between the Zeeman sublevels.…”