Photoemission electron microscopy of localized surface plasmons in silver nanostructures: Experiments and simulations

Abstract: In this work, spatially resolved localized surface plasmons (LSPs) in individual silver nanocubes and nanoellipsoids are imaged with a photoemission electron microscope (PEEM). Using broadband laser pulses with photon energies below the work function threshold of the material, multiphoton photoemission (MPPE) processes coupled to the LSPs governs the strong enhancement of the plasmonic near-field detected in the PEEM. For the nanocubes, the dependence of photoemission (PE) yield on laser polarization is investigated, and it is found that the local enhancement of the plasmonic near-field strongly depends on a superposition of localized plasmon modes excited in the nanocube. For the nanoellipsoids, the near-field dynamics are investigated using few-cycle laser pulses in an interferometric pump-probe setup, and it is found that the near-fields at the two ends of a particle dephase on a sub-3 fs timescale due to plasmon retardation across the particle. For both types of nanostructures, the results are supported by finite-difference time-domain electrodynamics simulations.