1,592 research outputs found
Optical manipulation of atoms and molecules using structured light
The interaction of atoms and molecules with structured light, specifically laser light endowed with the property of orbital angular momentum, such as Laguerre-Gaussian light, is discussed. The primary effects of interest here are the influence of the light on the gross motion of atoms and molecules and the possibilities this motion provides for particle manipulation in cooling, heating and trapping experiments. It turns out that, in addition to the possibility of modifying translational motion, suitably structured light can facilitate the manipulation of rotational motion. The latter possibility arises from a light-induced torque that is directly attributable to the orbital angular momentum property of the light. We outline the physics responsible for these effects and consider applications to typical cases in which atoms and ions are subject to near resonant Laguerre-Gaussian beams, leading to characteristic trajectories and eventual trapping in specific regions. Details are given for optical molasses configurations based on twisted light beams arranged in one-, two- and three-dimensional counter-propagating pairs. We extend consideration to the case of liquid crystals, subject to Laguerre-Gaussian light tuned far off-resonance, and show how this leads to the twisting of the directors in the liquid crystal, coinciding with the intensity distribution of the light
Optical orbital angular momentum
We present a brief introduction to the orbital angular momentum of light, the subject of our theme issue and, in particular, to the developments in the 13 years following the founding paper by Allen et al. (Allen et al. 1992 Phys. Rev. A 45, 8185 (doi:10.1103/PhysRevA.45.8185)). The papers by our invited authors serve to bring the field up to date and suggest where developments may take us next
Optical Surface Vortices and Their Use in Nanoscale Manipulation
Following a brief overview of the physics underlying the interaction of twisted light with atoms at near-resonance frequencies, the essential ingredients of the interaction of atoms with surface optical vortices are described. It is shown that surface optical vortices can offer an unprecedented potential for the nanoscale manipulation of absorbed atoms congregating at regions of extremum light intensity on the surface
Electrodynamics of Bose-Einstein condensates in angular motion
A theory determining the electric and magnetic properties of vortex states in
Bose-Einstein condensates (BECs) is presented. The principal ingredient is the
Lagrangian of the system which we derive correct to the first order in the
atomic centre of mass velocity. For the first time using centre of mass
coordinates, a gauge transformation is performed and relevant relativistic
corrections are included. The Lagrangian is symmetric in the electric and
magnetic aspects of the problem and includes two key interaction terms, namely
the Aharanov-Casher and the Roentgen interaction terms. The constitutive
relations, which link the electromagnetic fields to the matter fields via their
electric polarisation and magnetisation, follow from the Lagrangian as well as
the corresponding Hamiltonian. These relations, together with a generalised
Gross-Pitaevskii equation, determine the magnetic (electric) monopole charge
distributions accompanying an order n vortex state when the constituent atoms
are characterised by an electric dipole (magnetic dipole). Field distributions
associated with electric dipole active (magnetic dipole active) BECs in a
vortex state are evaluated for an infinite- and a finite-length cylindrical
BEC. The predictd monopole charge distributions, both electric and magnetic,
automatically satisfy the requirement of global charge neutrality and the
derivations highlight the exact symmetry between the electric and magnetic
properties. Order of magnitude estimates of the effects are given for an atomic
gas BEC, superfluid helium and a spin-polarised hydrogen BEC.Comment: 23 pages, 2 figures, submitted to Journal of Optics
Optical vortex singularities and atomic circulation in evanescent waves
The total internal reflection of an optical beam with a phase singularity can generate evanescent light that displays a rotational character. At a metalized surface, in particular, field components extending into the vacuum region possess vortex properties in addition to surface plasmon features. These surface plasmonic vortices retain the phase singularity of the input light, also mapping its associated orbital angular momentum. In addition to a two-dimensional patterning on the surface, the strongly localized intensity distribution decays with distance perpendicular to the film surface. The detailed characteristics of these surface optical vortex structures depend on the incident beam parameters and the dielectric mismatch of the media. The static interference of the resulting surface vortices, achieved by using beams suitably configured to restrict lateral in-plane motion, can be shown to give rise to optical forces that produce interesting dynamical effects on atoms or small molecules trapped in the vicinity of the surface. As well as trapping within the surface plasmonic fields, model calculations reveal that the corresponding atomic trajectories will typically exhibit a variety of rotational and vibrational effects, significantly depending on the extent and sign of detuning from resonance
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