  We briefly report on the recently proposed [G. Fiore, R. Fedele, U. de
Angelis, Phys. Plasmas 21 (2014), 113105], [G. Fiore, S. De Nicola,
arXiv:1509.04656] electron acceleration mechanism named "slingshot effect":
under suitable conditions the impact of an ultra-short and ultra-intense laser
pulse against the surface of a low-density plasma is expected to cause the
expulsion of a bunch of superficial electrons with high energy in the direction
opposite to that of the pulse propagation; this is due to the interplay of the
huge ponderomotive force, huge longitudinal field arising from charge
separation, and the finite size of the laser spot.
