Spatiotemporal Imaging of Surface Plasmons Using Two-Color Photoemission Electron Microscopy

Abstract

Time-resolved photoemission electron microscopy images recorded using a combination of ultrafast 800 nm (red) and 400 nm (blue) pulses track surface plasmon polaritons launched from lithographic patterns etched into silver thin films with joint femtosecond temporal and nanometer spatial resolution. The nondegenerate two-color scheme is found to significantly enhance photoelectron yields relative to single-color approaches. This enables both an enhanced visualization of surface plasmons and a more accurate determination of surface plasmon properties compared to single-color measurements. Power-dependent photoemission yield measurements reveal that the overall signal is linear with respect to blue excitation and slightly nonlinear for analogous red excitation. A numerical model based on wave packet propagation reproduces the experimental results and rigorously establishes that the polarization fields from both laser colors and their conjugate surface plasmons account for the observed photoelectron yield enh...