Abstract
The microwave-induced orbital angular momentum (OAM) transfer from a Laguerre-Gaussian (LG) beam to a weak plane-wave is studied in a closed-loop four-level ladder-type atomic system. The analytical investigation shows that the generated fourth field is an LG beam with the same OAM of the applied LG field. Moreover, the microwave-induced subluminal generated pulse can be switched to the superluminal one only by changing the relative phase of applied fields. It is shown that the OAM transfer in subluminal regime is accompanied by a slightly absorption, however, it switches to the slightly gain in superluminal regime. The transfer of light’s OAM and control of the group velocity of the generated pulse can prepare a high-dimensional Hilbert space which has a major role in quantum communication and information processing.
Highlights
In the past three decades, much attention has been paid to the study of the optical phenomena using Laguerre-Gaussian (LG) laser fields which are derived by solving the Helmholtz equation in the cylindrical coordinates
We present the results of our analytical calculations describing the orbital angular momentum (OAM) transfer from the strong coupling LG beam to a weak plane-wave via a weak planar microwave field
We focus on the coherence term ρ41, to investigate the spatially dependent absorption, intensity and phase profiles and group velocity of the microwave-induced generated fourth field (GFF)
Summary
Considering the initial conditions for the probe fields amplitudes at the atomic medium entrance as Ω41(z = 0) = 0 and Ω21(z = 0) = Ω21(0), and δ = 0, simultaneous solving of equations (3) and (4) leads to an explicit term for the Rabi frequency of the GFF as. According to equation (5), the phase factor of the strong coupling LG field transfers to the GFF, in the presence of two other planar fields. It is worth to note that, unlike the plane wavefront fields, the superluminal region for the LG pulses does determine by the anomalous dispersion and the OAM of the LG field affects the group velocity so that it may generate the superluminal light propagation even in the normal dispersion.
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