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

Surface plasmon optical vortices and their influence on atoms

An optical mode is generated in vacuum by the total internal reflection of a beam, at the planar surface of a dielectric on which a metallic film is deposited. When the beam impinging on the surface is a Laguerre–Gaussian (LG) mode, the resulting surface mode with field components in the vacuum region possesses vortex properties, in addition to surface plasmon features. Such surface plasmon optical vortex (SPOV) modes have well-defined orbital angular momentum, residing in an azimuthal phase relative to the propagation direction of the internally reflected light. Significantly, as SPOVs are characterized by a small mode volume, they can strongly couple to atomic or molecular systems in the vicinity of the surface. In particular, SPOVs generated by single or counter-propagating, symmetrically incident laser fields give rise to optical forces that can restrict the lateral in-plane motion of such atoms, thus acting as a trap. Typical atom trajectories, evaluated for sodium atoms initially localized in the vicinity of the metallized surface, exhibit a variety of rotational, vibrational and translational effects, as well as trapping

Optical ferris wheel for ultracold atoms

We propose a versatile optical ring lattice suitable for trapping cold and quantum degenerate atomic samples. We demonstrate the realisation of intensity patterns from pairs of Laguerre-Gauss (exp(i-ө) modes with different - indices. These patterns can be rotated by introducing a frequency shift between the modes. We can generate bright ring lattices for trapping atoms in red-detuned light, and dark ring lattices suitable for trapping atoms with minimal heating in the optical vortices of blue-detuned light. The lattice sites can be joined to form a uniform ring trap, making it ideal for studying persistent currents and the Mott insulator transition in a ring geometry