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Laser Physics

Distortion-free propagation in a chiral medium using the coherent superposition of atomic states

Sana Ullah, Fayaz Muhammad, Irfan Ullah, Bakht Amin Bacha, Sayed Arif Ullah

Published Oct 30, 2017• 5 citations
Publisher

Abstract

Abstract We propose a scheme for distortion free left/right circularly polarized beams in a chiral atomic medium in a tripod-type configuration using the superposition of atomic states. We measure and control the group index, group velocity and delay and advance times for left/right circularly polarized beams in a transparent chiral atomic medium by varying the population distribution probability in the superposition states. For the left and right circularly polarized beams of the probe field, delay and advance times have been observed at resonance and away from resonance. A negligible distortion and large phase shift in the left/right circularly polarized beams is theoretically investigated in the system. The results show potential applications in telecommunication, cloaking base technology and information processing.

DOI
10.1088/1555-6611/aa8ada

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Abstract We propose a scheme for distortion free left/right circularly polarized beams in a chiral atomic medium in a tripod-type configuration using the superposition of atomic states. We measure and control the group index, group velocity and delay and advance times for left/right circularly polarized beams in a transparent chiral atomic medium by varying the population distribution probability in the superposition states. For the left and right circularly polarized beams of the probe field, delay and advance times have been observed at resonance and away from resonance. A negligible distortion and large phase shift in the left/right circularly polarized beams is theoretically investigated in the system. The results show potential applications in telecommunication, cloaking base technology and information processing.
The structured vector fields of circularly polarized light , comprising both left and right (RCP and LCP) beams superposed in the atomic medium are investigated in this work. At resonance in the anomalous/normal dispersion area, both RCP and LCP beams with a non-negative and non-positive group index of ± 40 have been recorded. RCP and LCP beam group velocities are enhanced to ± 1 . 5 × 1 0 9 m / s at δ = 0 . 15 Γ , that is surpassing the speed of light in vacuum, denoted as ”c” leading to superluminal propagation. The RCP is superluminal and the LCP subluminal at the resonance point of the probe field. The group delay for The LCP beam is positive and the RCP beam is non-positive. The worth of the group delay for RCP and LCP beams varies to ± 4 n s . The superposing structured vectors field of superluminal and subluminal circularly polarized light beams on the right and left E R , L ( r , φ ) are strong variation function of detuning of probe field δ / Γ , Rabi frequency of control field Λ 3 / Γ and phase of collective driving fields φ . The results are useful for the modification of powerful computers.
Abstract This paper reports theoretical investigation of birefringence in a chiral medium for the creation of temporal cloaking. The chiral medium splits the input probe beam into left/right circular polarized beams. These left/right circular polarized beams are then controlled and modified within the chiral medium. The left circular polarized beam delays by 24 ns whereas the right circular polarized beam advances by −23 ns at a control field of rabbi frequency 6 γ . This opens a 47 ns time gap for temporal cloaking to hide information without noise corruption and energy loss. The results have potential applications in communication devices for secure propagation of light pulse.
Abstract We examine propagation of the linear polarized pulse through a medium containing four-level double V-type atoms. The medium is made chiral by the cross coupling of the applied electromagnetic fields. We show that such medium can be used as a polarization splitter of the probe pulse where the spatially refracted left and right circular polarized components propagate independently due to their distinct phase velocities. We find that dispersion characteristics of the chiral medium can be manipulated by the controlling parameters of the system. Consequently, both the left and right circular polarized components exhibit sub and superluminal propagation characteristics for suitable choices of the probe field detuning and external control fields. It is found that for both polarized components a switching from sub to superluminal behavior may be achieved by adjusting the probe field detuning. In addition, splitting of the left and right circular polarized components and hence peak value of the group time delay and advance may be tuned via the strengths of the control fields. Our results may find applications in spintronics, magnetic quantum optics, images coding and cloaking technology.
Abstract The absorption coefficients, refractive/group indices, phase shifts and fractional change of birefringence beams through dynamic chiral atomic medium are investigated under the effect of quantum tunnelling. The birefringence of phase indices Δ n = n r ( + ) − n r ( − ) and group indices Δ n g = n g ( + ) − n g ( − ) are controlled and modified through induced dynamic chiral medium by tunnelling effect. The group indices n g ( ± ) = ± 500 and group velocities v g ( ± ) = ± c / 500 are reported with the tunnelling effect. The maximum change in birefringent phase shifts is calculated to 5 microradian with tunnelling frequency at a speed of v = 10 cm/s of the chiral medium in the right circularly polarized (RCP) and left circularly polarized (LCP) beams. A 60% fractional change in the phase shift of RCP and LCP beams are investigated through induced chiral medium when the medium is at rest and when it is moving with the speed of v = 10 cm/s. These results will play an important role in scatterplate phase shifting interferometry.
We investigate the propagation of optical vector vortices of slow light in a coherently prepared four-level tripod atomic system. The vector vortex consists of superposed pulse pairs with opposite circular polarizations and orbital angular momentum (OAM) charges ±l\pm l±l, weakly interacting with an atomic medium initially prepared in a coherent superposition of two ground states. A third unoccupied state is coupled to a stronger control laser without OAM, creating a phase-dependent configuration. In the linear regime, the vortex OAM is mapped onto the medium, producing symmetrical azimuthally structured absorption patterns, with losses significantly reduced by the control field. For small detunings, complementary spatially dependent amplification and absorption occur for the two circular polarization components. This OAM-structured coherence induces a dynamical anisotropy, affecting both the intensity and polarization of the slow-light vortex. Polarization states evolve periodically between left-circular, linear, and right-circular polarizations during propagation. Once the beam reaches a stationary regime, the ring-shaped intensity transforms into a petal-like structure, and the final polarization states stabilize according to the initial superposition. The rate of polarization transitions is tunable via the control field strength, demonstrating flexible control over slow-light vector vortex dynamics.
Abstract The birefringence of rotary photon drags is investigated through induced chiral atomic medium. The birefringence of refractive and group indices, divergent angle and rotary photon drags were controlled and modified with detuning, phases and strength of Rabi frequencies of the driving fields. The value of divergent angle oscillated between ±0.01 radian with phases of control fields φ 3,4 and is minimum at φ 3 = π , while maximum at φ 4 = π . The right and left circularly polarized beams are drag clockwise due clockwise spinning of the medium in the normal dispersive region, while the right and left circularly polarized beams are drag clockwise due anticlockwise spinning of the medium in anomalous dispersive region. The maximum rotary photon drags of birefringent beams of light is calculated to ±5 milli radian. The results show advancement in molecular structure, dual image coding and image designing technology.