Onset of self-steepening of intense laser pulses in plasmas

Abstract

The self-steepening of laser pulses with intensities in excess of 1018 W cm-2 and with typical durations shorter than 30 fs propagating in underdense plasmas is examined by resorting to the framework of photon kinetics. Thresholds for self-steepening at the back/front of short laser pulses are determined, along with the self-steepening rates, and the connection between self-steepening, self-compression and frequency chirps is established. Our results are illustrated with particle-in-cell simulations, revealing the key physical mechanisms associated with the longitudinal laser dynamics, critical for the propagation of intense laser pulses in underdense plasmas.