Nonlinear relativistic interaction of an ultrashort laser pulse with a cold plasma

We investigate the nonlinear, relativistic dynamics that result when intense (1018W/cm2 and above) and ultrashort (one plasma period or shorter) laser pulse travels through a cold underdense plasma. Using a Lagrangian analysis of the plasma response, it can be demonstrated that the nonlinear wake, the collective dissipation, the nonlinear Compton losses, and the harmonic generation, are all determined by a finite set of integrated scalar quantities. This result holds for one-dimensional, short pulses of arbitrary amplitude, shape, and polarization, so that these very short intense laser pulses in a plasma can be viewed essentially as a quasiparticle characterized by a small set of global parameters