Directed Coulomb explosion effect on proton acceleration by an intense   laser pulse from a double-layer target
  We examine ion acceleration by irradiating a hundred TW laser pulse on a double-layer target. It is shown analytically and by three-dimensional particle-in-cell simulations that higher energy protons are obtained by using material with a high charge-to-mass ratio in the first layer of a double-layer target, because a strong Coulomb explosion occurs in such a material. As a result, the protons keep accelerating for a longer time. Using the optimal conditions for the target, it is shown that high energy and high quality protons can be generated. 
Toshimasa Morita, Sergei V. Bulanov, Timur Zh. Esirkepov, James Koga,   Masaki Kando
physics.plasm-ph physics.acc-ph