Numerical study of the wave-break in the vacuum-plasma interface during the interaction of an intense laser pulse

Abstract

In this paper, the wave break in the plasma-vacuum interface during the intense laser interaction is investigated. Since the nonlinear wave breaking is a non-adiabatic process, the fully kinetic 1D-3V Particle-In-Cell (PIC) simulation experiments are performed to identify whether that the origin of this mechanism is electromagnetic or electrostatic. Our simulation results show that the nonlinear wave breaking on the vacuum-plasma interface has electrostatic origin. In addition, it is found that for pulse lengths exceeding the plasma wavelength this electrostatic phenomenon comes in conjunction with some active electromagnetic effects having the same impact on the electron acceleration. In these regards, we conduct sophisticated simulations isolating these electromagnetic effects and study the effects of the pulse parameters such as the pulse rise time, pulse length, and pulse shape on the boundary nonlinear wave breaking. The study of the pulse rise-time variation effects shows that as the rise time of the laser pulse decreases, the number of the electrons involved in the nonlinear wave breaking, maximum energy of the trapped electrons and the path length of the accelerated electrons in the phase space are increased. Also, the study of phase space and field patterns in our simulation indicates that the reduction of the pulse flat top duration time causes that the smaller part of the electrons and the smaller portion of the wake wave involve in the nonlinear wave breaking.

Numerical investigation of plasma heating during the entrance of an intense short laser pulse into a density profile

“…Because of the density inhomogeneity, space-charge oscillations are subjected to nonlinear wave-brake in the vacuum-plasma interface [17]. This wave-brake formed at the vacuum-plasma interface toward the vacuum region, which is electrostatic in nature [16], and can accelerate electrons and could be considered as a generic mechanism being active at the front of the target spatially for a sharp step-like density profile. In the case of the laser pulse with τ L = 60 fs, the boundary wave-brake cannot be isolated and therefore, at the very early time of interaction, electrostatic effects such as the longitudinal field's oscillations along with the boundary wake-break could be possible acceleration mechanisms even in the absence of electromagnetic pulse evolution [23].…”

“…For this purpose, we have made a series of parametric simulations for different laser intensities and also variable scale lengths. Temporal evaluation of total radiations, figures 3(a) and (b), and normalized phase-space diagram, figures 3(c) and (d), have been depicted in the fully electromagnetic mode (EM) and electrostatic mode (ES) [16], for laser intensities ranging from a 0 = 2 to a 0 = 5 at 17.5 fs after interaction for the short scale length L p = 3 µm. We have chosen ES mode, to ignore the nonlinear pulse evolution effect and particularly to study electron acceleration at a phase-space diagram resulting from wave-break at the vacuum-plasma interface and longitudinal plasma oscillations.…”

“…It has been observed that a meaningful correlation exists between the density scale length and the observed spectrum of accelerated electrons [13]. A number of generically one-dimensional mechanisms have been suggested by many authors, including nonlinear wave-break in the vacuum-plasma interface [16,17], non-wake field interaction [18] and stochastic pattern [13,19,20].…”

“…It has been suggested that the wake-wave break at the vacuum-plasma interface (boundary wave break) could be predominant as a generic acceleration mechanism [16]. However, the nature and the contribution of nonlinear pulse evolutions, together with boundary wave breaking in electron acceleration and plasma heating, need to be further specified in detail at a very early time after interaction for pre-plasma with variable density scale lengths.…”