Plasma expansion studies in thin layer coated targets

Ion expansion analysis of the plasma produced from targets consisting of thin layers of aluminium on carbon substrates is used to estimate the thickness of the material ablated from the target. Ablation depth for aluminium in the flux range 1010-3x1012 w/cm2 (1GW Nd: glass laser, 5 nsec pulse) is around 1000A0 which is consistent with a steady state self regulatory, model for plasma heating. The total kinetic energy carried by the ions is estimated to be nearly 50% of the laser energy. Ion expansion velocity in case of bare targets scales with flux PHI as PHIsup(0.1) and PHIsup(0.35) in low and relatively higher flux range respectively. These variations in scaling which are different from PHIsup(2/9) scaling expected from a self regulatory model and relatively smaller kinetic energy with ions are shown to be occurring as a result of a significant fraction of absorbed laser energy being lost in X-ray emission from plasma. (author)