Third-harmonic spectroscopy and modeling of the nonlinear response of plasmonic nanoantennas.

We perform third-harmonic (TH) spectroscopy on rod-type gold nanoantenna arrays using widely tunable sub-30 fs laser pulses. We find the peak of the TH generation efficiency of the antenna arrays always slightly redshifted with respect to the peak of their linear extinction spectrum. We model the wavelength-dependent TH response quantitatively using a nonlinear harmonic oscillator model.