CONVECTIVE AMPLIFICATION OF WAKE-FIELD DUE TO SELF-MODULATION OF A LASER-PULSE INDUCED BY FIELD-IONIZATION

By using a particle-in-cell simulation code which includes tunneling i onization, it is found that strong wake fields are excited and amplifi ed due to the modulation of an intense laser pulse induced by an ioniz ing plasma in the regime where the matching condition between laser pu lse length (L-Laser) and plasma wavelength (lambda(p)), i.e. L-Laser l ess than or equal to lambda(p) is not satisfied. The modulation is cha racterized by a gradual steepening of the pulse front where then is a copropagating density gradient which is due to the rapid plasma format ion from ionization there. Accordingly, the wake field is convectively amplified to a significant level. This amplification of plasma waves always occurs, more or less, for laser propagation in ionizing plasmas . (C) 1998 American Institute of Physics.