Harmonics generation by surface plasmon polaritons on single nanowires

We present experimental observations of visible wavelength second- and third- harmonic generation on single plasmonic nanowires of variable widths. We identify that near infrared surface plasmon polaritons, which are guided along the nanowire, act as the source of the harmonics generation. We discuss the underlying mechanism of this nonlinear process, using a combination of spatially resolved measurements and numerical simulations to show that the visible harmonics are generated via a combination of both local and propagating plasmonic modes. Our results provide the first demonstration of nanoscale nonlinear optics with guided, propagating plasmonic modes on a lithographically defined chip, opening up new routes towards integrated optical circuits for information processing.