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

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-Λ 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.

Transfer of optical vortices in coherently prepared media

“…It has been recently shown that a double-Λ scheme can be employed for the exchange of optical vortices based on EIT [55]. In the double-Λ scheme there should be two additional control lasers of larger intensity to assure the exchange of optical vortices.…”

Orbital angular momentum transfer via spontaneously generated coherence

“…where γ R = γ L = γ. The parameter L is the length of the atomic medium and α defines the optical depth for both right and left fields [30]. Substituting Eq.…”

Microwave-induced orbital angular momentum transfer

“…Now, we are going to find the amplitude of the GFF using the Maxwell equations. In the slowly varying envelope approximation and assumption of time-independent probe fields the Maxwell equations for two weak probe fields, propagating in z direction, read towhere α and L are the optical depth of the probe fields and atomic vapor cell length, respectively 22 . Considering the initial conditions for the probe fields amplitudes at the atomic medium entrance as Ω 41 ( z = 0) = 0 and Ω 21 ( z = 0) = Ω 21 (0), and δ = 0, simultaneous solving of equations (3) and (4) leads to an explicit term for the Rabi frequency of the GFF asin whichandat z = 0.…”

“…Generation of the optical vortex beams from a non-vortex beam occurred by a wave mixing process in a nonlinear photonic crystal 15 . Several nonlinear optical processes have been studied in different quantum systems using LG beams 16 such as the second-harmonic generation 9,17 , sum frequency generation 18 , and four-wave mixing (FWM) 19–22 . The spatially structured optical transparency is theoretically investigated in a five-level combined tripod and Λ atom-light coupling scheme 23 .…”

“…In the following, it was shown that the OAM transfer from two vortex control fields to a probe field occurs in both four-level tripod-type and double tripod-type atomic systems 28,29 . Recently, the transfer of the optical vortex in four-level double-Λ EIT scheme, through a FWM process, has been reported only by one vortex control field 22 .…”