EXPERIMENTAL-OBSERVATIONS AND SIMULATIONS ON RELATIVISTIC SELF-GUIDING OF AN ULTRA-INTENSE LASER-PULSE IN UNDERDENSE PLASMAS

The experimental images of the sidescattered light from a plasma, crea ted by the multiterawatt laser pulse propagating in a hydrogen gas jet , exhibit clear dependence on both gas jet pressure and laser power. T wo- and three-dimensional simulations of wave propagation, in presence of the relativistic electron mass increase and the ponderomotive expe l of electrons, have been performed to reproduce the Thomson radiation from the plasma electrons. They show electron cavitation induced by t he beam focusing, self-focusing, self-guiding, smoothing of the beam n onuniformities and, at larger power, beam filamentation. A bremsstrahl ung model with account of the ionization, heating, expansion, and reco mbination dynamics of the gas, provides the plasma emission background . Both Thomson emission and bremsstrahlung are required to recover the experimental emission patterns. Among the interpretations, a scenario of laser self-guiding over five Rayleigh lengths can be found for 10 TW laser power and 5 x 10(18) cm(-3) electron density, which surprisin gly disappears at larger powers and densities. (C) 1996 American Insti tute of Physics.