title: Dissecting the Few-Femtosecond Dephasing Time of Dipole and Quadrupole Modes in Gold Nanoparticles Using Polarized Photoemission Electron Microscopy.
abstract: Dipole and quadrupole modes are the two lowest orders of localized surface plasmon resonance (LSPR) eigenmodes in metallic nanoparticles. Of these two modes, the quadrupole mode is forbidden for symmetric metallic nanoparticles excited by linearly polarized light at normal incidence. Here, we demonstrate excitation of the quadrupole mode in symmetrical gold (Au) nanoblocks shined with s-polarized light at oblique incidence. In particular, we probe the near-field LSPR in Au nanoblocks using photoemission electron microscopy (PEEM) and find that at oblique incidence, the dipole and quadrupole modes can be selectively excited, in terms of near-field enhancement, by manipulating the light polarization state. More importantly, by time-resolved PEEM measurements, we experimentally demonstrate that the quadrupole mode in symmetrical Au nanoblocks has longer dephasing time than that of the dipole mode.
authors.affiliation: Research Institute for Electronic Science, Hokkaido University , Sapporo 001-0021, Japan.|Creative Research Institution, Hokkaido University , Sapporo 001-0021, Japan.
authors.forename: Quan
authors.initials: Q
authors.lastname: Sun
authors.affiliation: Research Institute for Electronic Science, Hokkaido University , Sapporo 001-0021, Japan.
authors.forename: Han
authors.initials: H
authors.lastname: Yu
authors.affiliation: Research Institute for Electronic Science, Hokkaido University , Sapporo 001-0021, Japan.
authors.forename: Kosei
authors.initials: K
authors.lastname: Ueno
authors.affiliation: Institute of Physics, University of Tsukuba , Tsukuba 305-8571, Japan.
authors.forename: Atsushi
authors.initials: A
authors.lastname: Kubo
authors.affiliation: Research Institute for Electronic Science, Hokkaido University , Sapporo 001-0021, Japan.
authors.forename: Yasutaka
authors.initials: Y
authors.lastname: Matsuo
authors.affiliation: Research Institute for Electronic Science, Hokkaido University , Sapporo 001-0021, Japan.|Department of Applied Chemistry & Institute of Molecular Science, National Chiao Tung University , Hsinchu 30010, Taiwan.
authors.forename: Hiroaki
authors.initials: H
authors.lastname: Misawa
keywords: dark plasmon mode; dephasing; near-field imaging; photoemission electron microscopy (PEEM); surface plasmon resonance