Ion dynamics and coherent structure formation following laser pulse self-channeling

Abstract

The propagation of a superintense laser pulse in an underdense, inhomogeneous plasma has been studied numerically by two-dimensional particle-in-cell simulations on a time scale extending up to several picoseconds. The effects of the ion dynamics following the charge-displacement self-channeling of the laser pulse have been addressed. Radial ion acceleration leads to the 'breaking' of the plasma channel walls, causing an inversion of the radial space-charge field and the filamentation of the laser pulse. At later times a number of long-lived, quasiperiodic field structures are observed and their dynamics is characterized with high resolution. Inside the plasma channel, a pattern of electric and magnetic fields resembling both soliton-and vortex-like structures is observed.

Observation of Magnetized Soliton Remnants in the Wake of Intense Laser Pulse Propagation through Plasmas

“…These structures initially appear as a quasiperiodical pattern aligned along the lowdensity channel drilled by the laser pulse, and evolve on a time scale much longer than the pulse duration, remaining visible for more than 100 ps after the interaction. Simulations of the laser-driven plasma evolution carried out with a two-dimensional (2D) particle-in-cell (PIC) code show the development of EM solitons and their evolution into PSs inside laser-generated plasma channels [9]. Most noticeably the simulations indicate that, besides exhibiting properties typical of solitons (e.g., trapping of EM radiation in their inside and spatial localization consistent with the laser-pulse-depletion generation mechanism), these structures are also accompanied by vortexlike electron currents and quasistatic magnetic field patterns similar to those of MDVs.…”

“…In order to infer on the nature of the observed patterns, the interaction of the laser pulse with the He plasma and the following plasma evolution were modeled with 2D PIC simulations [9]. The simulations were performed in a range of plasma densities and laser pulse parameters close to the experimental ones.…”

“…In the following, lengths are in units of the laser wavelength , times in units of the laser period T L ¼ =c ¼ 2=!, densities in units of the critical density n c ¼ m e ! 2 =4e 2 , and field amplitudes are expressed in terms of the dimensionless parameter a ¼ eE=m e !c (see [9] for conversions to standard units). The largest grid employed in the simulations was a 7750 Â 2400 mesh with a spatial resolution of =10, and the simulations were running up to a time t ¼ 1500T L .…”

“…In the simulation a low-density channel is ponderomotively bored into the plasma by the laser pulse, with the channel breaking into a number of secondary narrower channels in the higher background density region [9]. Following the initial evolution [9,10] and after the laser pulse has exited the simulation box, both the ion and electron densities are left with a depression on the channel axis while peaking at the channel edges, giving rise to a space-charge separation electric field, mainly in the y direction, E y .…”

“…Following the initial evolution [9,10] and after the laser pulse has exited the simulation box, both the ion and electron densities are left with a depression on the channel axis while peaking at the channel edges, giving rise to a space-charge separation electric field, mainly in the y direction, E y . At this stage (t > 650T L ) E y has evolved into two ambipolar fronts on each side of the channel; i.e., it points outwards outside the channel and inwards inside it.…”