Simple model of the slingshot effect

We present a detailed quantitative description of the recently proposed slingshot eect". Namely, we determine a broad range of conditions under which the impact of a very short and intense laser pulse normally onto a low-density plasma (or matter locally completely ionized into a plasma by the pulse) causes the expulsion of a bunch of surface electrons in the direction opposite to the one of propagation of the pulse, and the detailed, ready-for-experiments features of the expelled electrons (energy spectrum, collimation, etc). The eect is due to the combined actions of the ponderomotive force and the huge longitudinal eld arising from charge separation. Our predictions are based on estimating 3D corrections to a simple, yet powerful plane 2-fluid magnetohydrodynamic (MHD) model where the equations to be solved are reduced to a system of Hamilton equations in one dimension (or a collection of) which become autonomous after the pulse has overcome the electrons. Experimental tests seem to be at hand. If conrmed by the latter, the eect would provide a new extraction and acceleration mechanism for electrons, alternative to traditional radio-frequency-based or Laser-Wake-Field ones.