Convective amplification of wake field due to self-modulation of a laser pulse induced by field ionization

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Abstract
By using a particle-in-cell simulation code which includes tunneling ionization, it is found that strong wake fields are excited and amplified due to the modulation of an intense laser pulse induced by an ionizing plasma in the regime where the matching condition between laser pulse length (LLaser) and plasma wavelength (λp), i.e. LLaser⩽λp is not satisfied. The modulation is characterized by a gradual steepening of the pulse front where there is a copropagating density gradient which is due to the rapid plasma formation 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.