Coupled Nanoantenna Plasmon Resonance Spectra from Two-Photon Laser Excitation

We report on the two-photon excitation and subsequent plasmonic mode relaxation of coupled optical gold nanoantennas. Using pulsed laser excitation at a constant wavelength of 810 nm, we observe two-photon-induced plasmon emission spectra, find them to match dark-field microscopy scattering spectra, and show that the emission intensity is enhanced by up to a factor of 65 compared to single gold rods of equal dimensions. This study shows the link of nonlinear optical excitation schemes with radiative relaxation pathways that match plasmonic mode emission of resonant optical gold antennas.