Controlling Surface Plasmon Propagation in Space and Time

We discuss directional control of surface plasmon polaritons (SPPs) propagating in space and time on noble metal surfaces using femtosecond laser photoemission electron microscopy (PEEM) and its and time-resolved variant. We demonstrate laser light coupling and interferometric focusing of SPPs using nanohole arrays and show how the array geometry (diameter, pitch, and number of rows/columns) influences plasmon focus and PEEM images. We demonstrate directed SPP launching, from both simple symmetric trench and hemispherical cap nanostructures. These studies reveal competition between SSPs and localized surface plasmon (LSP) modes and infer effects of laser polarization on the SPP and LSP coupling and interplay. Our time-resolved PEEM experiments use phase-locked femtosecond pump-probe pulses to generate movies with a 210 attosecond frame rate. The recorded movies of the PSP allow us to directly measure various SPP properties, including its carrier wavelength and group velocity (0.95c) in concert with finite-difference time domain simulations. Finally we discuss plasmon propagation across a material discontinuity (trench) and show enhanced plasmon signal detection using a heterodyne-like detection scheme.