Surface plasmon assisted electron acceleration in photoemission from gold nanopillars

Electron photoemission from lithographically prepared gold nanopillars using few-cycle, 800 nm laser pulses is measured. Electron kinetic energies are observed that are higher by up to tens of eV compared to photoemission from a flat gold surface at the same laser intensities. In addition, ionization from the nanopillar sample scales like a two-photon process, while three photons are needed to overcome the work function taking into account the shortest wavelength within the laser bandwidth. A classical electron acceleration model consisting of nonlinear ionization followed by field acceleration qualitatively reproduces the electron kinetic energy data and suggests average enhanced electric fields due to the nanopillars that are between 25 and 39 times greater than the experimentally used laser fields. Implications for plasmon-enhanced attosecond streaking are discussed. (c) 2012 Elsevier B.V. All rights reserved.