Resonant and Off-Resonant Light-Driven Plasmons in Metal Nanoparticles Studied by Femtosecond-Resolution Third-Harmonic Generation

We report on a femtosecond-resolution study of the plasmon fields in gold nanoparticles using third-harmonic generation. Controlled resonant and off-resonant plasmon excitation is achieved by tailoring the nanoparticle sample by an electron-beam-lithographic method. Comparing the measured third order interferometric autocorrelation function of the plasmon field with simulations based on a simple harmonic oscillator model we extract the temporal characteristic of the plasmon oscillation. For off-resonant excitation of particle plasmons we find a beating between the driving laser field and the plasmon field which demonstrates clearly the nature of the plasmon as a collective electron oscillation.