Transfer of optical vortices in coherently prepared media (original) (raw)
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Physical Review A, 2019
We propose a procedure to achieve a complete energy conversion between laser pulses carrying orbital angular momentum (OAM) in a cloud of cold atoms characterized by a double-Λ atom-light coupling scheme. A pair of resonant spatially dependent control fields prepare atoms in a positiondependent coherent population trapping state, while a pair of much weaker vortex probe beams propagate in the coherently driven atomic medium. Using the adiabatic approximation we derive the propagation equations for the probe beams. We consider a situation where the second control field is absent at the entrance to the atomic cloud and the first control field goes to zero at the end of the atomic medium. In that case the incident vortex probe beam can transfer its OAM to a generated probe beam. We show that the efficiency of such an energy conversion approaches the unity under the adiabatic condition. On the other hand, by using spatially independent profiles of the control fields, the maximum conversion efficiency is only 1/2.
Classical to quantum transfer of optical vortices
Optics Express, 2014
We show that an optical vortex beam, implemented classically, can be transferred to the transverse amplitude of a heralded single photon. For this purpose we have relied on the process of spontaneous parametric downconversion (SPDC) for the generation of signal and idler photon pairs, using a pump in the form of a Bessel-Gauss (BG) beam with orbital angular momentum (specifically, with topological charge l = 1 and l = 2). We have designed our source so that it operates within the short SPDC crystal regime for which, the amplitude and phase of the pump may be transferred to a heralded single photon. In order to verify the vortex nature of our heralded single photon, we have shown that the conditional angular spectrum and the transverse intensity at the single-photon level match similar measurements carried out for the pump. In addition, we have shown that when our heralded single photon is diffracted through a triangular aperture, the far-field singlephoton transverse intensity exhibits the expected triangular arrangement of intensity lobes associated with the presence of orbital angular momentum.
Generation of spatiotemporal optical vortices with controllable transverse orbital angular momentum
Nature Photonics, 2020
Today, it is well known that light possesses a linear momentum which is along the propagation direction. Besides, scientists also discovered that light can possess an angular momentum (AM), a spin angular momentum (SAM) associated with circular polarization and an orbital angular momentum (OAM) owing to the azimuthally dependent phase. Even though such angular momenta are longitudinal in general, a SAM transverse to the propagation has opened up a variety of key applications [1]. In contrast, investigations of the transverse OAM are quite rare due to its complex nature. Here we demonstrate a simple method to generate a three dimensional (3D) optical wave packet with a controllable purely transverse OAM. Such a wave packet is a spatiotemporal (ST) vortex, which resembles an advancing cyclone, with optical energy flowing in the spatial and temporal dimension. Contrary to the transverse SAM, the magnitude of the transverse OAM carried by the photonic cyclone is scalable to a larger value by simple adjustments. Since the ST vortex carries a controllable OAM in the unique transverse dimension, it has a strong potential for novel applications that may not be possible otherwise. The scheme reported here can be readily adapted for the other spectra regime and different wave fields, opening tremendous opportunities for the study and applications of ST vortex in much broader scopes.
Quadrupole absorption rate and orbital angular momentum transfer for atoms in optical vortices
Physical Review A
Recent experiments involving the interaction of optical vortices with atoms in quadrupole transitions have been shown to be accompanied by the exchange of orbital angular momentum (OAM) between the electronic states of the atom and the optical vortex field. Earlier work by both theory and experiment had ruled out the transfer of a vortex OAM to the electronic degrees of freedom in an electric dipole atomic transition and it has been confirmed that the lowest multipolar order involving an OAM transfer to the electronic motion is indeed the electric quadrupole. Hitherto, the quadrupole transition involving optical vortices has not been quantified and we have thus set out to evaluate the absorption rate accompanied by an OAM transfer with reference to the 6 2 S 1/2 → 5 2 D 5/2 in Cs when caesium atoms are subject to the field of a linearly polarized optical vortex. Our results assuming typical experimentally accessible parameters indicate that the absorption rate for moderate light intensities is smaller than the quadrupole spontaneous emission rate, but should still be within the measurement capabilities of modern spectroscopic techniques.
Laser beams with embedded vortices: tools for atom optics
Journal of The Optical Society of America B-optical Physics, 2006
Two-dimensional spatial light modulators have been employed to create static and dynamic phase masks for embedding multiple vortices and exotic intensity-void structures in laser beams. A variety of patterns of singularities, producing dark longitudinal and transverse intensity channels, have been created. The uniformity, quality, and suitability of these patterns as elements for atom optics (e.g., atom-tunnel beam splitters) have been studied as a function of the phase quantization level and spatial resolution of the phase mask. Specifically, we show that (1) high-quality modes, those that propagate long distances and can be focused, can be generated when the number of phase steps between 0 and 2 on the phase mask exceed four and (2) atom confinement increases with the charge of the vortex.
The optical manipulation of matter-wave vortices: An analogue of circular dichroism
2015
The transfer of orbital angular momentum from an optical vortex to an atomic Bose-Einstein condensate changes the vorticity of the condensate. The spatial mismatch between initial and final center-of-mass wavefunctions of the condensate influences significantly the two-photon optical dipole transition between corresponding states. We show that the transition rate depends on the handedness of the optical orbital angular momentum leading to optical manipulation of matter-wave vortices and circular dichroism-like effect. Based on this effect, we propose a method to detect the presence and sign of matter-wave vortex of atomic superfluids. Only a portion of the condensate is used in the proposed detection method leaving the rest in its initial state.
Angular momentum exchange between coherent light and matter fields
Physical Review A, 2008
Full, three dimensional, time-dependent simulations are presented demonstrating the quantized transfer of angular momentum to a Bose-Einstein condensate from a laser carrying orbital angular momentum in a Laguerre-Gaussian mode. The process is described in terms of coherent Bragg scattering of atoms from a chiral optical lattice. The transfer efficiency and the angular momentum content of the output coupled vortex state are analyzed and compared with a recent experiment.
Momentum transfer in a standing optical vortex
A field superposition of singular beams incident on, and then reflected from a mirror has been investigated. It was demonstrated that the standing optical wave, which contains a vortex, possesses an orbital angle momentum where the energy flux circulates only in the azimuth direction of the beam. We show in this paper that the standing light wave containing the optical vortex transfers angular momentum to a substance located in the field of the vortex without moving the substance in the azimuth or radial directions. This property of the standing vortex present an opportunity to form the three-dimensional optical traps, gasdynamic and hydrodynamic vortices, in a localised volume by a direct transfer of the orbital angular momentum from the optical vortex. (3)), so that the axis of symmetry of the mirror is coincident with the z-axis of the beam, and the centre of curvature is on the axis at a distance z' from the mirror. The mirror surface is in accordance with the wavefront of Eq.(2). It can be shown from Eq.(3) that the reflectivity of the beam from the mirror, and the centre of curvature in the point ! z = z / , is equivalent to the reflectivity
Physical Review A, 2016
The exchange of orbital angular momentum (OAM) between paraxial optical vortex and a Bose-Einstein condensate (BEC) of atomic gases is well known. In this paper, we develop a theory for the microscopic interaction between matter and an optical vortex beyond paraxial approximation. We show how superposition of vortex states of BEC can be created with a focused optical vortex. Since, the polarization or spin angular momentum (SAM) of the optical field is coupled with OAM of the field, in this case, these angular momenta can be transferred to the internal electronic and external center-of-mass (c.m.) motion of atoms provided both the motions are coupled. We propose a scheme for producing the superposition of matter-wave vortices using Gaussian and a focused Laguerre-Gaussian (LG) beam. We study how two-photon Rabi frequencies of stimulated Raman transitions vary with focusing angles for different combinations of OAM and SAM of optical states. We demonstrate the formation of vortex-antivortex structure and discuss interference of three vortex states in a BEC.
Transfer of orbital angular momentum of light using two-component slow light
Physical Review A, 2013
We study the manipulation of slow light with an orbital angular momentum propagating in a cloud of cold atoms. Atoms are affected by four copropagating control laser beams in a double tripod configuration of the atomic energy levels involved, allowing to minimize the losses at the vortex core of the control beams. In such a situation the atomic medium is transparent for a pair of copropagating probe fields, leading to the creation of two-component (spinor) slow light. We study the interaction between the probe fields when two control beams carry optical vortices of opposite helicity. As a result, a transfer of the optical vortex takes place from the control to the probe fields without switching off and on the control beams. This feature is missing in a single tripod scheme where the optical vortex can be transferred from the control to the probe field only during either the storage or retrieval of light.