Transfer of optical vortices in coherently prepared media

Abstract

We consider transfer of optical vortices between laser pulses carrying orbital angular momentum (OAM) in a cloud of cold atoms characterized by the Λ configuration of the atom-light coupling.The atoms are initially prepared in a coherent superposition of the lower levels, creating a so-called phaseonium medium. If a single vortex beam initially acts on one transition of the scheme, an extra laser beam is subsequently generated with the same vorticity as that of the incident vortex beam.The absorption of the incident probe beam takes place mostly at the beginning of the atomic medium within the absorption length. The losses disappear as the probe beam propagates deeper into the medium where the atoms are transferred to their dark states. The method is extended to a tripod atom-light coupling scheme and a more general n + 1-level scheme containing n ground states and one excited state, allowing for creating of multiple twisted light beams. We also analyze generation of composite optical vortices in the scheme using a superposition of two initial vortex beams and study lossless propagation of such composite vortices.

Off-axis optical vortices using double-Raman singlet and doublet light-matter schemes

“…It should be noted that the diffraction terms containing the transverse derivatives have been neglected in the Maxwell equations ( 3) and ( 4). These terms are negligible if the phase change of the probe fields due to these terms is much smaller than π [23,59,60].…”

“…The phase of the on-axis optical vortices advances linearly and monotonically with the azimuthal coordinate reaching a multiple of 2π after completing a closed circle around the beam axis. When two twisted beams each carrying an optical vortex are superimposed, the resulting beam contains new vortices depending on the charge of each vortex component [60,[66][67][68]. Besides the on-axis vortices, the off-axis optical vortices can be formed for which the vortex core is not on the beam axis but moves about it [68][69][70][71][72].…”

Complete energy conversion between light beams carrying orbital angular momentum using coherent population trapping for a coherently driven double- Λ atom-light-coupling scheme

“…The phase singularity at the beam core of the twisted beam renders its donut-shaped intensity profile. A number of interesting effects appear when this type of optical beams interact with the atomic systems [27][28][29][30][31][32][33][34][35][36][37][38][39][40][41][42][43]. Among them optical vorticities of slow light [35,39,40,42,44] have caused a considerable interest, as the OAM brings a new degree of freedom in manipulation of the optical information during the storage and retrieval of the slow light [45,46].…”

“…It has been demonstrated that without switching off and on of the control fields, transfer of optical vortices take place by applying a pair of weaker probe fields in the closed loop double-Λ [35] or double-tripod [39] schemes. The exchange of optical vortices in non-closed loop structures has been recently shown to be possible under the condition of weak atom-light interaction in coherently prepared atomic media [41]. Such a medium is known as the phaseonium [47][48][49][50][51][52][53].…”

Azimuthal modulation of electromagnetically induced grating using structured light

“…The light-matter interaction using optical vortices results also in light-induced-torque 40 , second harmonic generation 41 , four-wave mixing 42 , spatially dependent EIT 43,44 , and vortex slow light 45,46 . Exchange of OAM modes in multi-level quantum systems has been extensively studied by the Juzeliūnas group [47][48][49][50] , while these schemes were recently extended also to applications in semiconductor quantum-dot molecules 51 and semiconductor quantum wells 52,53 .…”