Plasma inhomogeneity effects on particles energization by high-power laser pulse in a finite-size plasma

Abstract

In this paper, the plasma inhomogeneity effects on the nonlinear laser energy absorption in a finite-size plasma have been studied in details, using two-dimensional relativistic electromagnetic PIC (Particle-In-Cell) simulation code. To this end, the effects of inhomogeneity characteristics on the nonlinear phenomena involved in the nonlinear laser absorption such as phase-mixing, wave-breaking, and parametric instabilities have been investigated. The simulation results show that the inhomogeneity causes the phase-mixing time to be reduced, in agreement with the results of recent theoretical works. As a more significant result, it is illustrated that although the plasma inhomogeneity increases the nonlinear absorption of laser in a finite-size plasma at the early time due to the phase-mixing/wave-breaking phenomenon, it eventually reduces the absorption rate because of the growth of parametric instabilities, in contrast to the interaction of laser with an infinite plasma where the laser scattering enhances the laser energy absorption. The results of the present investigation can greatly contribute to the further progression of knowledge in the experiments on the interaction of high-power lasers with inhomogeneous finite-size plasmas where the laser energy absorption is of crucial importance.