Simultaneous Experimental Observation of the Quantization and the Interference Pattern of a Plasmonic Near-Field

Tom Lummen Laboratory for Ultrafast Microscopy and Electron Scattering, École Polytechnique Fédérale de Lausanne, Lausanne, Vaud, Switzerland Luca Piazza Laboratory for Ultrafast Microscopy and Electron Scattering, École Polytechnique Fédérale de Lausanne, Lausanne, Vaud, Switzerland Erik Quiñonez Department of Physics, Trinity College, Hartford, Connecticut, USA Yoshie Murooka Laboratory for Ultrafast Microscopy and Electron Scattering, École Polytechnique Fédérale de Lausanne, Lausanne, Vaud, Switzerland Bryan Reed Physical and Life Sciences Directorate, Lawrence Livermore National Laboratory, Livermore, California, USA Brett Barwick Department of Physics, Trinity College, Hartford, Connecticut, USA Fabrizio Carbone Laboratory for Ultrafast Microscopy and Electron Scattering, École Polytechnique Fédérale de Lausanne, Lausanne, Vaud, Switzerland

Miniaturized plasmonic and photonic integrated circuits are generally considered as the core of future generations of optoelectronic devices, due to their potential to bridge the size-compatibility gap between photonics and electronics. However, as the nanoscale is approached in increasingly small plasmonic and photonic systems, the need to experimentally observe and characterize their behavior in detail faces increasingly stringent requirements in terms of spatial and temporal resolution, field of view, and acquisition time. This work focuses on a specific electron microscopy technique, Photon-Induced Near-Field Electron Microscopy (PINEM), which is capable of imaging optical evanescent fields and surface plasmon polaritons (SPPs) in nanoplasmonic structures with both nanometer and femtosecond resolution. To do so, an advanced electron energy filter is used to analyze the quantized energy exchange between a photo-induced SPP and an ultra-short bunch of probing electrons. In electron energy loss/gain spectroscopy mode, the exchange of up to 30 photon quanta with the photo-induced SPPs in silver nanoantennae is observed. In PINEM imaging mode, the spatial properties of the photo-induced standing SPP wave on a single silver nanoresonator are shown to be controlled by the polarization of the optical pump pulse. These results are guided and corroborated by extensive 3D finite-element modeling. Moreover, in a novel hybrid acquisition mode - which synchronously characterizes the electron-SPP interaction along both a spatial coordinate and energy - both the characteristic spatial interference and the energy quantization of the SPP are obtained in the same experiment, providing a unique visualization of the wave-particle duality of its electromagnetic near-field.

tom.lummen@epfl.ch