Plasmonic near-field spatiotemporal characterizations of an asymmetric copper bowtie nanostructure

Photon-induced near-field electron microscopy (PINEM), developed from ultrafast transmission electron microscopy, enables near-field imaging with nanometer spatial resolution and femtosecond temporal resolution. We report the plasmonic near-field distribution and lifetime analysis for an asymmetric copper bowtie nanostructure having unequal opening angles. The PINEM images show surface plasmon polaritons and local surface-plasmon resonance excitations with various polarizations. Combined with finite-element simulations, the polarization- and structure-dependent distribution and intensity variations of the near-field were analyzed. The lifetime difference of a plasmonic near-field excited by different polarizations is also discussed. The temporal and spatial characterization of the plasmonic near-field is important for the further studies of plasmonic near-field manipulation and designs of plasmonic devices having specific functions.