Plasmon-enhanced four-wave mixing by nanoholes in thin gold films.

Nonlinear plasmonics opens up for wavelength conversion, reduced interaction/emission volumes, and nonlinear enhancement effects at the nanoscale with many compelling nanophotonic applications foreseen. We investigate nonlinear plasmonic responses of nanoholes in thin gold films by exciting the holes individually with tightly focused laser beams, employing a degenerated pump/probe and Stokes excitation scheme. Excitation of the holes results in efficient generation of both narrowband four-wave mixing (FWM) and broadband multiphoton excited luminescence, blueshifted relative to the excitation beams. Clear enhancements were observed when matching the pump/probe wavelength with the hole plasmon resonance. These observations show that the FWM generation is locally excited by nanoholes and has a resonant behavior primarily governed by the dimensions of the individual holes.