Nanostructured Potential of Optical Trapping Using a Plasmonic Nanoblock Pair

We
performed two-dimensional mapping of optical trapping potentials experienced
by a 100 nm dielectric particle above a plasmon-resonant gold nanoblock
pair with a gap of several nanometers. Our results demonstrate that
the potentials have nanoscale spatial structures that reflect the
near-field landscape of the nanoblock pair. When an incident polarization
parallel to the pair axis is rotated by 90°, a single potential
well turns into multiple potential wells separated by a distance smaller
than the diffraction limit; this is associated with super-resolution
optical trapping. In addition, we show that the trap stiffness can
be enhanced by approximately 3 orders of magnitude compared to that
with conventional far-field trapping.