The modulation effect of transverse, antibonding, and higher-order longitudinal modes on the two-photon photoluminescence of gold plasmonic nanoantennas.

Plasmonic nanoantennas exhibit various resonant modes with distinct properties. Upon resonant excitation, plasmonic gold nanoantennas can generate strong two-photon photoluminescence (TPPL). The TPPL from gold is broadband and depolarized, and may serve as an ideal local source for the investigation of antenna eigenmodes. In this work, TPPL spectra of three arrays of single-crystalline gold nanoantennas are comprehensively investigated. We carefully compare the TPPL spectra with dark-field scattering spectra and numerically simulated spectra. We show the modulation effect of the transverse resonant mode and the nonfundamental longitudinal mode on the TPPL spectrum. We also demonstrate suppression of TPPL due to the subradiant antibonding modes and study the influence of antenna resonant modes on the overall TPPL yield. Our work provides direct experimental evidence on nanoantenna-mediated near-to-far-field energy coupling and gains insight into the emission spectrum of the TPPL from gold nanoantennas.