Toward a self-consistent model of the interaction between an ultra-intense, normally incident laser pulse with an overdense plasma

Following a recent work by Sanz et al. [Phys. Rev. E 85, 046411 (2012)], we elaborate upon a one-dimensional model describing the interaction between an ultra-intense, normally incident laser pulse and an overdense plasma. The analytical solutions of the reflected laser field, the electrostatic field, and the plasma surface oscillation are obtained within the cold-fluid approximation. The high-order harmonic spectrum is calculated from the exact solution of the plasma surface oscillations. In agreement with particle-in-cell simulations, two regimes of harmonic generation are predicted: for moderately relativistic laser intensities, or high plasma densities, the harmonic spectrum is determined by the discontinuity in the derivative of the reflected field when the electron plasma boundary oscillates across the fixed ion boundary. For higher intensities, the electron plasma boundary is confined inside the ion region and oscillates at relativistic velocities, giving rise to a train of reflected attosecond pulses. In both cases, the harmonic spectrum obeys an asymptotic omega(-4) scaling. The acceleration of electrons and the related laser absorption efficiency are computed by a test particle method. The model self-consistently reproduces the transition between the "anomalous skin effect" and the "J x B" heating predicted by particle-in-cell simulations. Analytical estimates of the different scalings are presented. (C) 2013 AIP Publishing LLC.