  Remote excitation and emission of two-photon luminescence and second-harmonic
generation are observed in micrometer long gold rod optical antennas upon local
illumination with a tightly focused near-infrared femtosecond laser beam. We
show that the nonlinear radiations can be emitted from the entire antenna and
the measured far-field angular patterns bear the information regarding the
nature and origins of the respective nonlinear processes. We demonstrate that
the nonlinear responses are transported by the propagating surface plasmon at
excitation frequency, enabling thereby polariton-mediated tailoring and design
of nonlinear responses.
