Highlights from particle-in-cell simulations of superintense laser-plasma interactions

A selection of results from particle-in-cell simulation of laser-plasma interactions in two and three spatial dimensions are presented. The generation of coherent, long-living electromagnetic structures and the 3D dynamics of selfchanneling have been studied in low-density plasmas. The acceleration of ions driven by radiation pressure in high-density, thin targets is also investigated

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

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, quasi-periodic 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.Comment: 10 pages, 5 figures (visit http://www.df.unipi.it/~macchi to download a high-resolution version), to appear in Plasma Physics and Controlled Fusion (Dec. 2007), special issue containing invited papers from the 34th EPS Conference on Plasma Physics (Warsaw, July 2007

Radiation Pressure Acceleration by Ultraintense Laser Pulses

The future applications of the short-duration, multi-MeV ion beams produced in the interaction of high-intensity laser pulses with solid targets will require improvements in the conversion efficiency, peak ion energy, beam monochromaticity, and collimation. Regimes based on Radiation Pressure Acceleration (RPA) might be the dominant ones at ultrahigh intensities and be most suitable for specific applications. This regime may be reached already with present-day intensities using circularly polarized (CP) pulses thanks to the suppression of fast electron generation, so that RPA dominates over sheath acceleration at any intensity. We present a brief review of previous work on RPA with CP pulses and a few recent results. Parametric studies in one dimension were performed to identify the optimal thickness of foil targets for RPA and to study the effect of a short-scalelength preplasma. Three-dimensional simulations showed the importance of ``flat-top'' radial intensity profiles to minimise the rarefaction of thin targets and to address the issue of angular momentum conservation and absorption.Comment: 11 pages, 8 figures, accepted for publication to the special issue "EPS 2008" of PPC

Surface Oscillations in Overdense Plasmas Irradiated by Ultrashort Laser Pulses

The generation of electron surface oscillations in overdense plasmas irradiated at normal incidence by an intense laser pulse is investigated. Two-dimensional (2D) particle-in-cell simulations show a transition from a planar, electrostatic oscillation at $2\omega$, with $\omega$ the laser frequency, to a 2D electromagnetic oscillation at frequency $\omega$ and wavevector $k>\omega/c$. A new electron parametric instability, involving the decay of a 1D electrostatic oscillation into two surface waves, is introduced to explain the basic features of the 2D oscillations. This effect leads to the rippling of the plasma surface within a few laser cycles, and is likely to have a strong impact on laser interaction with solid targets.Comment: 9 pages (LaTeX, Revtex4), 4 GIF color figures, accepted for publication in Phys. Rev. Let

On the production of flat electron bunches for laser wake field acceleration

We suggest a novel method for injection of electrons into the acceleration phase of particle accelerators, producing low emittance beams appropriate even for the demanding high energy Linear Collider specifications. In this paper we work out the injection into the acceleration phase of the wake field in a plasma behind a high intensity laser pulse, taking advantage of the laser polarization and focusing. With the aid of catastrophe theory we categorize the injection dynamics. The scheme uses the structurally stable regime of transverse wake wave breaking, when electron trajectory self-intersection leads to the formation of a flat electron bunch. As shown in three-dimensional particle-in-cell simulations of the interaction of a laser pulse in a line-focus with an underdense plasma, the electrons, injected via the transverse wake wave breaking and accelerated by the wake wave, perform betatron oscillations with different amplitudes and frequencies along the two transverse coordinates. The polarization and focusing geometry lead to a way to produce relativistic electron bunches with asymmetric emittance (flat beam). An approach for generating flat laser accelerated ion beams is briefly discussed.Comment: 29 pages, 5 figure

Relativistic electromagnetic solitons produced by ultrastrong laser pulses in plasmas

Low frequency, relativistic sub-cycle localised (soliton-like) concentrations of the electromagnetic (em) energy are found in two-dimensional (2D) and in three-dimensional (3D) Particle in Cell simulations of the interaction of ultra-short, high-intensity laser pulses with homogeneous and inhomogeneous plasmas. These solitons consist of electron and ion density depressions and intense em field concentrations with a frequency definitely lower than that of the laser pulse. The downshift of the pulse frequency , due to the depletion of the pulse energy, causes a significant portion of the pulse em energy to become trapped as solitons, slowly propagating inside the plasma. In a earlier phase solitons are formed due to the trapping of the em radiation inside an electron cavity, while ions can be assumed to remain at rest. Later on, after (m_i/m_e)1/2 times the laser period, ions start to move and the ion depletion occurs producing a slowly growing hole in the plasma density. In inhomogeneous plasmas the solitons are accelerated toward the plasma vacuum interface where they radiate away their energy in the form of the bursts of low frequency em radiation. In the frame of a 1D cold hydrodynamic model for an electron-ion plasma, the existence of multipeaked em solitons has been investigated both analytically and numerically. The analytical expression for a sub-cycle relativistic soliton has been derived for circularly polarized pulses in a cold isotropic plasma, and in the presence of an externally applied magnetic field. Recently, em relativistic solitons in a hot multi-component plasma have been investigated in the frame of an hydrodynamic (adiabatic) model and of a kinetic (isothermal) model. An overview of the most recent analytical and numerical results on the soliton dynamics is give

Plasma Ion Evolution in the Wake of a High-Intensity Ultrashort Laser Pulse

International audienceExperimental investigations of the late-time ion structures formed in the wake of an ultrashort, intense laser pulse propagating in a tenuous plasma have been performed using the proton imaging technique. The pattern found in the wake of the laser pulse shows unexpectedly regular modulations inside a long, finite width channel. On the basis of extensive particle in cell simulations of the plasma evolution in the wake of the pulse, we interpret this pattern as due to ion modulations developed during a two-stream instability excited by the return electric current generated by the wakefield