The influence of pre-pulse plasma on ion and x-ray emission from Ta plasma produced by a high-energy laser pulse

The paper describes studies of ion and x-ray emissions from plasma produced by the PALS laser system at different parameters of pre-plasma generated by a laser pre-pulse. The plasma was produced by 0.4-ns laser pulses of about 140 J at 438 nm (3rd harmonic frequency) focused on a slab Ta target. The main laser pulse was preceded by a pre-pulse having either 0.7 main-pulse energy. The main pulse was delayed by 0.6 ns, 1.2 ns, 2.3 ns, or 4.6 ns with reference to the prepulse. The characteristics of the ion streams (energies, charge states and angular distributions of ion emission) were investigated using diagnostics based on the time-of-flight method. The x-rays were measured using various types of semiconductor detectors covered with different filters. It was found that, at small delay times, Δt 0.2 A cm−2 at 1 m) ion stream having angular divergence and ion energy spread significantly smaller than those for the case without the pre-pulse.