  The use of nanophotonics for optical manipulation has continuously attracted
interest in both fundamental research and practical applications, due to its
significantly enhanced capabilities at the nanoscale. In this work, we showed
that plasmonic particles can be trapped at off-axis location in Gaussian beams
assisted by surface plasmon resonance. The off-axis displacement can be tuned
at the sub-wavelength scale by the incident light beams. Based on these, we
propose that a superfast orbital rotation of particles in continuous-wave laser
beam can be realized in tightly focused circularly polarized Gaussian beams.
The rotation has a tunable orbital radius at the sub-wavelength scale and a
superfast rotation speed (more than 10^4 r/s in water under common laboratory
conditions). Our work will aid in the development of optically driven
nanomachines, and find applications in micro/nano-rheology, micro-fluid
mechanics, and biological research at the nanoscale.
