| 研究実績の概要 |
The extraordinary optical properties of coupled plasmonic nanostructures make these materials potentially useful in many applications. Coupled plasmon modes have been characterized predominantly using far-field spectroscopy. In near-field spectroscopy, the spectral response of local field enhancement in coupled plasmonic nanostructures remains largely unexplored, especially experimentally. Here, we have experimentally investigated the coupled gold dolmen nanostructures in near fields using photoemission electron microscopy (PEEM) with wavelength-tunable femtosecond laser pulses as the excitation source.
The spatial evolution of near-field mapping of an individual dolmen structure with the excitation wavelength was successfully obtained by our unique PEEM measurements, and the near-field plasmon coupling could be revealed. In particular, the evolution of the near-field patterns at high spatial resolution with the excitation wavelength revealed that the coupled bonding and anti-bonding plasmon modes hybridize from a dipole mode in the monomer part and the quadrupole mode in the dimer part. We observed that the hybrid anti-bonding and bonding modes dominated the near-field enhancement. Furthermore, the measurement of near-field spectral properties allow to distinguish the difference between Fano resonances and plasmon hybridization. The results deepen our understanding of plasmon hybridization and plasmonic Fano resonances and are expected to facilitate further development of potential applications.
|
