Electron Emission from Metal Surfaces Excited by Intense Femtosecond Pulses

Abstract

Electron emission from a metal surface excited by an intense visible laser pulse can be attributed to thermionic emission, thermally assisted photoemission, or quantum excitation channels (multiphoton photoemission). With intense sub-picosecond laser excitation, thermionic emission due to highly non-equilibrium electron heating can be the dominant process because of the small electronic heat capacity and brief uncoupling between the electron and lattice, as first predicted by Anisimov et al1. Experimental observations of such transient thermionic emission could potentially serve as a diagnostic of peak electron temperature Te. However, their interpre­tation is rendered difficult because the large electron emission rate introduces tremendous space-charge fields at the surface, which substantially suppress the electron yield, while simultaneously distorting the detected electron energy distribution from the initial thermal distribution. In order to understand quantitatively the electron yield and energy distribution in the intense femtosecond pulse regime and to develop a useful diagnostic technique, we present a combined experimental, analytical theory, and particle-simulation investigation of femtosecond pulse induced electron emission from Al, Ag and W surfaces. Both the analytical theory and simulation work incorporate the strong space-charge fields present in the experiment.