Regensburg 2010 – wissenschaftliches Programm
DS 27.8: Vortrag
Mittwoch, 24. März 2010, 12:15–12:30, H32
Dark-Mode Plasmonic Nanorod Cavity — •Johannes Kern, Swen Großmann, Jer-Shing Huang, Paolo Biagioni, and Bert Hecht — Experimental Physics 5, University of Würzburg, Germany
We report ultra-small nanoplasmonic cavities consisting of a self-assembled, side-by-side aligned gold nanorod dimer. The rods are 50-70 nm long and are separated by a 3 nm gap. The structure corresponds to a finite piece of a two-wire transmission line with two highly reflective open ends which supports a quasi-TE fundamental mode which propagates along the transmission line. Reflection at the end caps leads to length-dependent Eigenmodes, whose energies are determined by the cavity length and the phaseshift introduced upon reflection. Unlike the dipolar longitudinal and transverse plasmon resonances that are also supported by the structure, the fundamental cavity mode is a dark quadrupol mode.
Nevertheless the cavity mode is experimentally accessible by excitation of electron-hole pairs in the gold bandstructure, which act as local dipole sources. The ultra-small mode volume and comparatively high Q-factor leads to a high selectivity of the cavity and the electron-hole pairs preferentially decay into the cavity resonance. Therefore luminescence spectra of the cavities clearly show the peak of the cavity mode. The wavelength of the cavity mode depends on the cavity length and lies in the VIS region, consistent with FDTD simulations and analytical modeling.
The ultra-small mode volume and high Q-factor make our cavities promising candidates to study lasing and/or strong coupling effects.