Ultrahigh intensity laser-plasma interaction: A Lagrangian approach

A Lagrangian analysis simplifies considerably the description of the ultrahigh intensity regime of laser-plasma interaction, and facilitates the identification of several new and important effects. First, the vacuum figure "8" orbit is shown to be unstable, with respect to a stochastic instability leading to collisionless heating. Second, in the generation of plasma wakes using ultrahigh intensity laser pulses, it can be shown that, for long-duration laser pulses, the plasma wake is insignificant, but, through proper phasing of a set of short-duration pulses, a dramatic amplification of the wake amplitude occurs. Third, in the generation of third-harmonic waves using ultrahigh intensity, long-duration laser pulses, it can be seen that a mismatch in the phase velocity limits severely the power conversion, but a conversion efficiency free from saturation might indeed be possible by employing either a density-modulated plasma or an ionized buffer gas.