Particle-in-cell simulations indicate that attosecond electron bunches are efficiently generated when relativistically strong tightly focused p-polarized laser pulses interact with sharp boundaries of over-dense plasmas. This effect is demonstrated with 15 fs laser pulse incident obliquely at 70^o on a plasma layer (Fig.1). Under the action of the incident and reflected wave the electron concentration is abruptly peaked. A group of counterstreaming electrons is pushed away from the plasma through nulls in the electromagnetic field. These electrons inherit a peaked density distribution and form relativistic ultrashort bunches in vacuum. Escaping the target with relativistic velocities, electrons in their turn compress the reflected radiation, generating the train of attosecond electromagnetic pulses. The synchronism of attosecond electromagnetic pulses and attosecond electron bunches increases their applicability, opening the path to relativistic attosecond optoelectronics.

Fig.1 Attosecond electron bunches (energies between 20 and 30MeV shown) generated synchronously with attosecond electromagnetic pulses.

References:

1) Attosecond Electron Bunches
N. Naumova, I. Sokolov, J. Nees, A. Maksimchuk, V. Yanovsky, and G. Mourou Phys. Rev. Lett. 93, 195003 (2004).
American Physical Society abstract