Relativistic electron generation in laser produced ion channels

Abstract

This contribution is concerned with the channeling of a relativistic laser pulse propagating in an underdense plasma, and with the subsequent generation of fast electrons in the cavitated ion channels. Specifically, we study the interaction of laser pulses of duration of several 10 2 femtoseconds, having their intensity I λ 2 in the range [10 19 ; 10 20 ] Wcm −2 μm 2 and focused in underdense plasmas, with electron densities n 0 such that the ratio n 0 = n c lies in the interval [10 −3 , 10 −1 ], n c denoting the critical density. The laser power P L exceeds the critical power for laser channeling P ch = 1:09 P c , P c denoting the critical power for relativistic self-focusing. The laser-plasma interaction under such conditions is investigated by means of three dimensional (3D) Particle-In-Cell (PIC) simulations. It is observed that the steep laser front gives rise to the excitation of a surface wave which propagates along the sharp radial boundaries of the electron free channel created by the laser pulse. The mechanism responsible for the generation of relativistic electrons observed in the PIC simulations is then analyzed by means of a 3D test particles code. The fast electrons are thus found to be generated by the combination of the electron acceleration caused by the surface wave and of the betatron mechanism. The maximum electron energy observed in the simulations is scaled as a function of P L / P c ; it reaches 350 - 400 MeV for P L / P c = 70 - 140.