The wakefield generation and electrons acceleration in the interaction of femtosecond chirped and double laser pulses with an underdense thin plasma slab is examined by numerical solution of the relativistic Vlasov-Maxwell system of equations using the backward semi-Lagrangian method (BSL). Unlike particle-in-cell methods, the BSL method is free of numerical noise and provides an accurate representation of the distribution function, even in very low density regions of phase space where acceleration and trapping occur. The effect of density fluctuations in low density regions of phase space are important, since they affect the acceleration processes over the following interactions. Therefore, a detailed structure of the distribution function is needed to investigate this process in these regions, which only can be obtained by Vlasov codes. Excitation of wakefields by chirped, chirp free, and double pulse lasers in an underdense plasma slab are simulated using the BSL code and the results are compared. It is shown that by making use of chirped laser pulses, the mean kinetic energy of plasma electrons can be enhanced up to 40% compared with the chirp free case. The investigation of wakefield generation by double laser pulses with a time repetition equal to one plasma period, exhibits amplification of wakefield amplitude after the entrance of the second laser pulse into plasma slab.
Magnetic fields from high-intensity laser pulses in plasmas