Tunable plasmon modes in single silver nanowire optical antennas characterized by far-field microscope polarization spectroscopy

Performing far-field microscope polarization spectroscopy and
finite element method simulations, we investigated experimentally
and theoretically the surface plasmon modes in single Ag nanowire
antennas. Our results show that the surface plasmon resonances in
the single Ag nanowire antenna can be tuned from the dipole plasmon
mode to a higher order plasmon mode, which would result in the
emission with different intensities and polarization states, for
the semiconductor quantum dots coupled to the nanowire antenna. The
fluorescence polarization is changed with different polarized
excitation of the 800 nm light beam, while it remains parallel to
the Ag nanowire axis at the 400 nm excitation. The 800 nm incident
tight interacts nonresonantly with the dipole plasmon mode with the
polarized excitation parallel to the Ag nanowire axis, while it
excites a higher order plasmon mode with the perpendicular
excitation. Under excitation of 400 nm, either the parallel or
perpendicular excitation can only result in a dipole plasmon mode.
In addition, we demonstrate that the single Ag nanowire antenna can
work as an energy concentrator for enhancing the two-photon excited
fluorescence of semiconductor quantum dots.