Hot electron generation enhancement by long duration positive chirped laser pulses

Interaction of the chirped circularly polarized laser pulse with ramped density plasma is presented by particle-in-cell simulation. The obtained results indicate that the laser penetration depth into the plasma target and hot-electron generation can be improved by chirped induced transparency (CIT). Positive chirped pulses penetrate more deeply in the plasma leading to the hot electron enhancement and improvement of the maximum separation accelerating fields at the rear side of the target. For laser pulse with 150 fs time duration, there is 40% increase in the laser penetration depth in the target and the maximum amount of the electrostatic field is improved by a factor of 5 in the present of optimum chirp parameter. It is also noticed that the effect of CIT is more prevailing for long duration pulses. Penetration depth, electron heating and maximum of the electrostatic fields are promoted significantly by introducing positive chirp to pulses with longer duration. Although, the unchirped laser pulses with intensity lower than the self-induced transparency threshold cannot propagate through the plasma directly, the long duration chirped pulses can compensate low intensities and induce the lasers penetration by irradiating the long positive chirp pulses with suitable intensity. (paper)