A Space-Time Analysis of Electron Emission From a Focusing Structure for Surface Plasmon Polaritons Using Photoemission Microscopy

A circular grating coupler on a single-crystalline Au platelet is used to create surface plasmon polariton waves with spherical phase fronts that form a focal point in the center of the circle. In a time-resolved photoemission microscopy experiment, the propagation and interaction of plasmon waves in the focusing structure is investigated with sub-femtosecond time-resolution. Several space-time signatures of propagating and transiently formed standing plasmon waves are identified. The method of contrast enhancement for the data-analysis is discussed, and all observed experimental features are explained. In addition to the known electron emission from the nonlinear superposition of light and plasmon field, we also observe plasmoemission signatures, i.e., emitted electrons that arise from a nonlinear emission process driven purely by the plasmonic field.