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.