In a recent experiment Shegai et al.1 have shown that a bimetallic particle dimer composed of gold and silver atoms may work as a directional frequency filter which scatters light of different frequencies in different directions. A phase difference between emitters required for the directional scattering of light was determined by the complex particle polarizabilities and therefore varies with the size, shape and material composition of the particles in accordance with their plasmon resonance characteristics. In this paper, we give a theoretical explanation of the experimental results in terms of interference between light fields emitted by nonidentical radiators.
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.