Laser Wake Field Acceleration of relativistic electron bunches is a
promising method to produce a large amount of energetic particles with
table top equipment. One of the possible methods to inject particles in
the appropriate acceleration phase of the wake behind the pulse takes
advantage of the partial longitudinal breaking of the wake crests
across a density downramp. In this paper results of 2.5D PIC
simulations, showing the production of an electron bunch with reduced
energy spread, are reported. Also, a possible method to produce the
required plasma density transition by laser explosion of a suitable
couple of thin foils is discussed.