Two-Photon Luminescence of Gold Nanorods Mediated by Higher Order Plasmon Modes

Metallic nanorod antennas can be considered as an analogue to classical half-wave dipole antennas, constituting an important tool for manipulating linear and nonlinear light-matter interactions in nanoscale volumes. Using two-photon luminescence (TPL) scanning laser microscopy, we investigate such optical antennas beyond their fundamental dipole mode. The antenna mode dispersion is extracted from the nonlinear TPL measurement and reveals a TPL process that is dominated by plasmon-induced enhancement of the two-photon absorption in the metal. Additionally, a clear signature of the mode parity is observed in the TPL images. TPL maxima are observed outside the antenna boundaries for even parity modes, whereas they are located inside for odd modes. It is concluded that for even modes the two-photon luminescence emission is strongly mediated by retardation of the excitation field, a consequence moment. This selective excitation of different mode parities is highly relevant for nanoscale enhanced nonlinear of their zero net-dipole optics, as well as plasmonic nanosensor applications and tuning of radiative properties of quantum emitters.