Density effects on collimation of energetic electron beams driven by two intense laser pulses

When an intense laser pulse irradiates solid targets, the light energy is deposited at the relativistic critical density and relativistic electrons are produced. However, these fast electrons are generally divergent. In this paper, a scheme to reduce the divergence of laser-driven energetic electron beams in solid-density plasmas is investigated by two-dimensional particle-in-cell simulation. In the scheme, two intense laser pulses and a plasma target consisting of two parts with different densities are employed. The first laser pulse induces a strong interface magnetic field by generating fast electron flow along the density interface. The magnetic field collimates the electrons generated by the second laser pulse. The simulation results show that the strong interface magnetic field can change the direction of the energetic beam electrons and considerably reduce their divergence. (C) 2009 American Institute of Physics. [DOI: 10.1063/1.3112706]