  The power-flow lines of light interacting with a metallic nanoparticle, in
the proximity of its plasmon resonance, form whirlpool-like nanoscale optical
vortices. Two different types of vortex have been detected. The outward vortex
first penetrates the particle near its centerline then, on exiting the
particle, the flow-lines turn away from the centerline and enter a spiral
trajectory. Outward vortexes are seen for the wavelengths shorter then the
plasmon resonance. For the wavelengths longer that the plasmon resonance the
vortex is inward: the power-flow lines pass around the sides of the particle
before turning towards the centerline and entering the particle to begin their
spiral trajectory.
