Ultrafast Time-Resolved Spatial Mapping of Field-Enhanced Two-Photon Photoemission from Metal Surfaces (original) (raw)

Abstract

ABSTRACT Field enhancement effects at metallic nanostructures are crucial for experimental techniques such as surface-enhanced Raman spectroscopy and scanning near-field optical microscopy that detect optical signals (e.g., due to Raman scattering, surface plasmon resonances, fluorescence, or frequency mixing) to interrogate surface chemical and physical interactions at the nanoscale. However, the spatial resolution of these all- optical techniques is limited to tens of nanometers due to the low photon yield from small sample volumes. We report on a new approach that uses the probe tip of a scanning tunneling microscope to detect electrons emitted during time-resolved ultrafast laser excitation of a metal surface. We show how we have used this technique to image two-photon field enhancements near the surfaces of single nanoparticles with sub-nanometer spatial resolution. We also describe how this approach may enable the simultaneous sub-nanometer spatial and sub- picosecond temporal resolution of surface electron dynamics.

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