Evanescent-wave acceleration of femtosecond electron bunches

A 150-fs 800-nm 1-mu J laser was used to excited surface plasmons in the Kr etschmann geometry in a 500-Angstrom silver film. Multiphoton excitation re sults in the emission of femtosecond electron bunches (40 fC) as had been s een before. The electron beam is highly directional and perpendicular to th e prism surface. A time-of-flight setup has been used to measure the kineti c-energy distribution of the photoelectrons. Surprisingly, we find that thi s distribution extends to energies as high as 40 eV. Theoretical calculatio ns show that these high energies may be due to acceleration in the evanesce nt laser held that extends from the silver film out into the vacuum. These results suggest that femtosecond pulses with more energy per pulse or longe r wavelength may be used to accelerate electrons to the keV or even MeV lev el. (C) 2000 Elsevier Science B.V. All rights reserved.