Ionization, ion distribution, and ion focusing in laser plasmas from atomic and diatomic targets

Charge-resolved measurements of the total number of particles from plasmas produced from planar, monoatomic targets of copper and tungsten as well as the binary targets of copper and tungsten are reported, using a 125mJ, 5ns, Nd:YAG laser, at a laser intensity of about 1010W∕cm2. The measurements show a severe quenching of the ionization states in the case of the diatomic targets. These measurements and their variations with ionization state support the theoretical investigations of plasma motion under the influence of the viscous force in case of plasmas consisting of light and heavy particles. Gaussian width measurements of the angular particle distribution showed a focusing effect towards the target normal, the width decreasing as the ion mass and ionization state increased. From the analysis of the theoretical results on self-similarity expansion it is concluded that the ion acceleration due to the built-in electrostatic potential is not significant.