Exchange of optical vortices using an electromagnetically induced transparency based four-wave mixing setup

TL;DR

This paper presents a simplified method for exchanging optical vortices of slow light via electromagnetically induced transparency in a four-level atomic system, enabling efficient orbital angular momentum transfer without switching control fields.

Contribution

It introduces a new, simpler scheme for optical vortex exchange using EIT and four-wave mixing, avoiding the need for control fields with opposite helicity.

Findings

Orbital angular momentum can be transferred between beams via FWM in EIT.

Losses depend on one-photon detuning and can be minimized.

Phase mismatch effects on vortex exchange are manageable.

Abstract

We propose a scheme to exchange optical vortices of slow light using the phenomenon of electromagnetically induced transparency (EIT) in a four-level double-$\Lambda$ atom-light coupling scheme illuminated by a pair of probe fields as well as two control fields of larger intensity. We study the light-matter interaction under the situation where one control field carries an optical vortex, and another control field has no vortex. We show that the orbital angular momentum (OAM) of the vortex control beam can be transferred to a generated probe field through a four-wave mixing (FWM) process and without switching on and off of the control fields. Such a mechanism of OAM transfer is much simpler than in a double-tripod scheme in which the exchange of vortices is possible only when two control fields carry optical vortices of opposite helicity. The losses appearing during such OAM exchange are then calculated. It is found that the one-photon detuning plays an important role in minimizing the losses. An approximate analytical expression is obtained for the optimal one-photon detuning for which the losses are minimum while the intensity of generated probe field is maximum. The influence of phase mismatch on the exchange of optical vortices is also investigated. We show that in presence of phase mismatch the exchange of optical vortices can still be efficient.