Dependency of the stochastic heating of electrons on the pulse rise-time in intense laser-plasma interaction

In this paper, the effects of the pulse rise-time in the performance of the electron heating in the interaction of intense laser pulse with under-dense plasma have been investigated using the particle-in-cell (PIC) simulation code. In this way, two laser pulses with a length of 200 fs and different pulse rise-time of 80 fs and 40 fs have been selected. The laser intensity and the plasma density are I=1018 w/cm2 and n=0.02 ncr (ncr is the plasma critical density), respectively. To correctly characterize the local plasma temperature in different regions of plasma, the stress tensor elements have been used. Our results show that the electron heating and the temperature of the electrons are strongly dependent on the laser pulse rise-time and increase significantly with decreasing the pulse rise-time. In other words, when the pulse rise-time is initially smooth (80 fs), the scattering fields can provide the necessary condition for stochastic heating. Whereas, in the quickly rising pulses (40 fs), the electron heating is initiated by the wave breaking. In the following, the effect of increasing the laser pulse intensity on the electron heating is investigated for the pulses with different rise-times, hence these effects are more severe for the pulses with the short rise-time.