Raman-induced transfer of optical vortices

We explore the concept that the Raman process can be used as an effective way for transfer of optical vortices. In a four-level atomic system, two strong fields are applied to form a Λ-type subsystem while two probe fields couple to the other cascade transitions. It is found that the optical vortex of a control field can be transferred to a generated probe beam based on four-wave mixing processes, wherein the one-photon detuning plays an important role in minimizing the losses. On the other hand, when the control fields have no vortices, the transfer is realized between two probe beams for intermediate values of atomic coherence induced by the Raman process, vanishing both for the minimal value 0 and for the maximal values ±0.5. We have also analyzed the spatial structures of the propagating probe beams with optical vortices at the entrance, displaying that the information of winding numbers is hidden behind the intensity distributions and corresponding phase patterns. This may find potential applications in quantum information storage.