Contour plots of electron density 2D PIC in units of

1. Relativistic self-focusing, electron acceleration and ultra-short laser pulse propagation in underdense plasmas 1 2 1 1 2 1 Neda Naseri , Paul-Edouard Masson-Laborde , Valery Bychenkov, Wojciech Rozmus , University of Alberta , Lebedev Physics Institute Abstract Wave breaking, acceleration (SP) Relativistic fluid model Self Focusing,Channeling Contour plot of electron density 2D PIC (SP). The picture on the left shows the wave breaking and the picture on the right shows injected electrons. Model equations in 1D: Maxwell + Full Hydro + Poisson Theoretical studies and particle-in-cell (PIC) simulations of nonlinear processes related to short pulse laser propagation in underdense plasmas. For the laser power above critical power for relativistic self-focusing in two spatial dimensions PIC simulation results converge to stationary laser filaments. Conditions for the formation of multifilament structures are discussed and demonstrated in simulations for relatively long pulses. For short laser pulses nonlinear propagation at relativistic intensities involves pulse erosion, frequency shift and characteristic steepening at the front of the pulse. Different mechanisms of particle acceleration are described including particle trapping at the front of the pulse, acceleration by the plasma wake fields and by the electromagnetic wave. These processes are simulated and discussed in the context of recent experiments with gas jet targets on the ALLS facility. wake • Underdense homogeneous plasma • Fixed ions • Maxwell’s equations+Equation of motion • Assuming laser pulse Maxwell Equation injected electrons wave breaking Hydro: continuity + motion equations These equations can be solved analytically in 2D (F. Cattani et al, PRE, 2001). Poisson equation Partial electron evacuation Complete evacuation Contour plots of electron density 2D PIC in units of Blue:electron density Relativistic self-focusing Pulse erosion, 1D in hydro Red: longitudinal electric field [n |e|] cr green: laser field half of channel width Strong steepening of longitudinal field Snapshots of laser intensity cross section Contour plot of Laser intensity 2D PIC (SP) wave breaking Pulse Field Density Longitudinal Field accelerating field pulseerosion Maximum intensity is 3 times bigger than maximum initial Intensity (SP). parameters as SP • Numerical models • Particle-in-cell code MANDOR (1D , 2D): Romanov et al. PRL, 2004 • Relativistic cold plasma approximation and Maxwell equations in 1D-limited by the absence • of kinetic effects • Standard parameters (SP) - consistent with experimental conditions: pulse duration, =30fs, spot size=13m, intensity, I=4*1018 W/cm2, density, n=5* 1019 cm-3, p-polarized. • The experiment carried out at the Advanced Laser Light Source (Z. L. Chen, Y. Y. Tsui, R. Fedosejves) • Homogeneous plasma slab with 40 microns linear ramp in the front. 400-800 microns in length - propagation distance is limited by laser pulse scattering and absorption. Wave-breaking and electron acceleration Numerical Results channel evacuated of electrons Phase space at time= 1031 fs Accelerated electrons After wave-breaking electrons are accelerated and injected into the pulse and the accelerating field. 4.8% of total number of electrons are accelerated. contour plot of electron density trapped electrons bubble accelerated electrons DLA electrons in front Comparison with theoretical results: time=1395 fs Plot of electron density vs. y accelerating field energy of accelerated electrons Red points correspond to analytical solution pulse erosion Greens and blue points correspond to • numerical results dN/dE [Arb. Units] 25 Mev evacuated channel n bubble at later time accelerated electrons cavity pulse erosion • From laser plasma accelerators, quasi monoenergetic • 70 – 170 MeV, Mangles et al. Nature 2004, Geddes et al. • ibid 2004, Faure et al. ibid 2004. Electron energy in ev Electron energy spectrum Phase space Strong electrostatic wake Filamentation of intense laser beam in plasma 100 Mev In 2D PIC, data taken from a cut along x in the middle of the box. Laser pulse enters from left and propagates along x. electrons in back of bubble By using transversely flat modulated laser pulse, filamentation instability is being studied. electrons in front part of bubble Laser pulse as it enters the plasma electrons in back of bubble dN/dE [Arb. Units] DLA electrons electrons in front part of bubble longitudinal filed 180 Mev E x Input modulated laser pulse Simulation parameters: Energy in ev DLA electrons Electron energy in ev Laser intensity (eE/mc) Contour plots of Laser intensity 2D PIC (SP) a in unit of(eE/mc) Threshold power for bubble regime electron density Gordienko, phys plasmas, 2005 I=1020,=20fs, n=1019cm-3 Laser pulse after propagating 240 micrometers P[TW] bubble filaments Contour plot of electron density 2D PIC (SP) in units of filaments Contour plot of Laser intensity 2D PIC a in unit of(eE/mc) [n |e|] cr Laser intensity (eE/mc) I=4 1018,=30fs, n=5 1019cm-3 ALLS [fs]