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Alexandria Engineering Journal

Enhanced quadrupole effects for atoms in surface spiral beams with a thin dielectric waveguide

S. Al‐Awfi

Published Apr 29, 2022• 6 citations
Publisher

Abstract

Recently, some physical research has recognized the coupling of optical phase singularity light with quadrupole-active atomic transitions. We show that a Laguerre-Gaussian beam, when completely internally reflected at the dielectric/vacuum interface, can generate a well-defined surface spiral beam with a two-dimensional intensity distribution confined to a sub-wavelength region near the interface outside of the dielectric. The quadrupole interaction has been shown to be significantly enhanced in the case of coating the planar surface of a dielectric prism using multilayer dielectric thin films of different thicknesses. The mechanical action on the atom due to the optical forces characterized by optical quadrupole transitions could greatly facilitate the revolution of optical manipulation of neutral atoms along the dielectric/vacuum interface. The typical optical quadrupole potential, evaluated for the atomic transition, corresponds to λ=675.0nm with ΓQ=7.8×105s-1, in Cesium atoms, which is a dipole-forbidden but quadrupole-allowed transition. The parameters used to compute the optical quadrupole potential are similar to those in recent experiments. The factors controlling the general enhancement are pointed out and discussed.

DOI
10.1016/j.aej.2022.04.035

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Recently, some physical research has recognized the coupling of optical phase singularity light with quadrupole-active atomic transitions. We show that a Laguerre-Gaussian beam, when completely internally reflected at the dielectric/vacuum interface, can generate a well-defined surface spiral beam with a two-dimensional intensity distribution confined to a sub-wavelength region near the interface outside of the dielectric. The quadrupole interaction has been shown to be significantly enhanced in the case of coating the planar surface of a dielectric prism using multilayer dielectric thin films of different thicknesses. The mechanical action on the atom due to the optical forces characterized by optical quadrupole transitions could greatly facilitate the revolution of optical manipulation of neutral atoms along the dielectric/vacuum interface. The typical optical quadrupole potential, evaluated for the atomic transition, corresponds to λ=675.0nm with ΓQ=7.8×105s-1, in Cesium atoms, which is a dipole-forbidden but quadrupole-allowed transition. The parameters used to compute the optical quadrupole potential are similar to those in recent experiments. The factors controlling the general enhancement are pointed out and discussed.
The total internal reflection of a light with phase singularity, such as Laguerre–Gaussian (LG) light, can generate an evanescent wave. The distribution of this type of light is firmly localized in the vicinity above the dielectric surface and displays a rotational character. Any atom approaching the surface from the vacuum region interacts with evanescent wave and produces interesting rotational effects. Recent studies have established the coupling of LG beams to both electric atomic transitions; dipole and quadrupole according to the selection rules of each, permitted and prohibited. Due to the small magnitude of the quadrupole interaction compared to the dipole interaction, we chose the two counter-propagating beams configuration to generate the doubling Rabi frequencies with more stable surface optical forces. We describe the essential rotational features and discuss how they can be used to influence atoms. Atom confinement and dynamics in the interaction of surface optical vortices with the two different atomic transitions are illustrated using typical experimentally accessible parameters for the case of the Cs atom interacts with the LG10 mode.
Recent studies have involved electric quadrupole effects in atoms interacting with the evanescent mode. This type of surface mode is usually produced by the total internal reflection in a dielectric-vacuum atz=0, and its intensity distribution is very close to the outer surface z>0 half-space. Coating the planar surface of a dielectric substrate with multilayer dielectric thin film of different thicknesses provides an enhanced in such evanescent modes. This type of mode can be used purely as an atomic mirror. We show that the use of such elements for atomic optics gives significant enhancement of the evanescent mode magnitude without degrading the quality of the atomic reflection process. In addition, the decay depth of the evanescent mode can be conveniently controlled by design parameters. This property keeps the atom-light interaction timeτ, and thus the probability of decay emission, very low, which means a high degree of coherence property.
Recently it has been shown that the quadrupole interactions can be improved significantly as the atom interacts at near resonance with the Laguerre-Gaussian (LG) mode. In this paper, we illustrate that other kinds of optical vortex can be also led to a considerable enhancement of quadrupole interaction when the atom interacts with optical modes at near resonance. The calculations are performed on an interesting situation with Cs atom, where the process is concerned with dipole-forbidden and quadrupole-allowed transitions with a convenable choice of atomic and optical mode parameters. In this direction, we show that the quadrupole transitions can be significantly enhanced and therefore they can play an interesting role and lead to new features of atom-light interaction, which can have some constructive implications in experiments.
We explain how quadrupole-active atomic interactions be able to be enhanced once the neutral atom interacts with an evanescent winding light modes. The optical system presented is a semi-bounded space based on neutral atoms situated close to the evanescent Bessel-Gaussian modes. The quadrupole Rabi frequency (and hence the optical quadrupole potential) generated by such evanescent modes is large enough to be exploited in atoms manipulation. In particular, the atomic states in which the dipole transitions are prohibited but the quadrupole transitions are permissible create the optical quadrupole potential of accessible value to play an important role. It is also shown how such optical system acts to create of evanescent modes with ℓ>0 having an orbital angular momentum ℓℏ in which the intensity distribution is restricted in the vicinity of the dielectric surface.
The evanescent light field created by total internal reflection at a dielectric-vacuum interface has tight spatial confinement and high local intensity.These properties become more robust when a dual layer of dielectric thin films with different thicknesses is deposited on a planar dielectric surface.Optical construction is promising in nanoscale trapping of absorbed atoms congregating at extreme light field intensity distribution regions on the dielectric surface.Here, we theoretically demonstrate the controllable two-dimensional surface optical lattices based on the evanescent electric field generated by the Hermite-Gaussian light beam.By considering the coupling of lattice to quadrupole-active atomic transitions, we show that the topologies cannot just have high stability, but also the optical potential deep, and thus the dynamic trapping can be governed by changing the design parameters of the optical construction.We expect that this study may contribute to providing another unique method for fabricating spatially complicated two-dimensional nanostructures.
Recent studies have confirmed the coupling of optical vortices, such as Laguerre-Gaussian and Bessel-Gaussian modes, to quadrupole-active atomic transitions. This interaction has been shown to be enhanced considerably in the case of Laguerre-Gaussian beams due to the gradient coupling, particularly, in the case of a relatively large winding number. Here, we consider the trapping and the dynamics of atoms in the optical quadrupole potential generated by two coaxial counterpropagating optical vortex beams. We focus on the atomic transition $6{\phantom{\rule{0.16em}{0ex}}}^{2}{S}_{1/2}\ensuremath{\rightarrow}5{\phantom{\rule{0.16em}{0ex}}}^{2}{D}_{5/2}$ in Cs which is a dipole-forbidden but a quadrupole-allowed transition. We show how this atomic transition engages with the optical vortex fields at near resonance, leading to atom trapping in the optical quadrupole potential well accompanied by translational motion. We show how the optical forces generate the motion of the atoms trapped within the quadrupole potential, illustrating the results using typical experimentally accessible parameters.