Evanescent-wave acceleration of ultrashort electron pulses

High-power femtosecond laser pulses have been used to excite surface plasmo ns in 500 Angstrom silver and gold films. Nonlinear excitation results in t he emission of electron bunches through multiphoton excitation at low power and laser-induced field emission at high power. The energies of photoelect rons are found to extend as high as 0.4 keV. Calculations show that these h igh energies are due to ponderomotive acceleration in an evanescent field e xtending from the metal film out into the vacuum. The theoretical calculati ons suggest that femtosecond electron pulses with relativistic energies can be generated using longer wavelengths or by developing the surface morphol ogy. (C) 2001 American Institute of Physics.