Abstract

The new generation of short duration lasers provides pulses in excess of the terawatt level, that can be focused up to 10¹⁸ W/cm² [1]. For such an intensity, the quiver motion of a free electron becomes relativistic and numerous new physical effects are expected, such as harmonic generation [2], particle acceleration [3] and relativistic self-focusing [4,5]. In order to observe these effects resulting from laser-electron interaction, a high electron density (N_e) is required. In fact, with regard to the small laser-electron interaction cross-section, a large number of electrons is needed for any significant field emission. Furthermore, using a high density, a collective response of electrons is driven that induces intense longitudinal fields required to accelerate particles. A significant change of the refractive index should also occur that will influence beam propagation if the electron density is large enough.

© 1994 Optical Society of America