title: Mode imaging and selection in strongly coupled nanoantennas.
abstract: The number of eigenmodes in plasmonic nanostructures increases with complexity due to mode hybridization, raising the need for efficient mode characterization and selection. Here we experimentally demonstrate direct imaging and selective excitation of the "bonding" and "antibonding" plasmon mode in symmetric dipole nanoantennas using confocal two-photon photoluminescence mapping. Excitation of a high-quality-factor antibonding resonance manifests itself as a two-lobed pattern instead of the single spot observed for the broad "bonding" resonance in accordance with numerical simulations. The two-lobed pattern is observed due to the fact that excitation of the antibonding mode is forbidden for symmetric excitation at the feedgap, while concomitantly the mode energy splitting is large enough to suppress excitation of the "bonding" mode. The controlled excitation of modes in strongly coupled plasmonic nanostructures is mandatory for efficient sensors, in coherent control as well as for implementing well-defined functionalities in complex plasmonic devices.
authors.affiliation: Nano-Optics and Biophotonics Group, Experimentelle Physik 5, Physikalisches Institut, Wilhelm-Conrad-Röntgen-Center for Complex Material Systems, Universität Würzburg, Am Hubland, D-97074 Würzburg, Germany. jhuang@physik.uni-wuerzburg.de
authors.forename: Jer-Shing
authors.initials: JS
authors.lastname: Huang
authors.forename: Johannes
authors.initials: J
authors.lastname: Kern
authors.forename: Peter
authors.initials: P
authors.lastname: Geisler
authors.forename: Pia
authors.initials: P
authors.lastname: Weinmann
authors.forename: Martin
authors.initials: M
authors.lastname: Kamp
authors.forename: Alfred
authors.initials: A
authors.lastname: Forchel
authors.forename: Paolo
authors.initials: P
authors.lastname: Biagioni
authors.forename: Bert
authors.initials: B
authors.lastname: Hecht