Normal-Incidence Photoemission Electron Microscopy (NI-PEEM) for Imaging Surface Plasmon Polaritons

We introduce a novel time-resolved photoemission-based near-field illumination method, referred to as femtosecond normal-incidence photoemission microscopy (NI-PEEM). The change from the commonly used grazing-incidence to normal-incidence illumination geometry has a major impact on the achievable contrast and, hence, on the imaging potential of transient local near fields. By imaging surface plasmon polaritons in normal light incidence geometry, the observed fringe spacing directly resembles the wavelength of the plasmon wave. Our novel approach provides a direct descriptive visualization of SPP wave packets propagating across a metal surface.