Energy transfer and expansion dynamics of a collisional laser plasma from planar, atomic and binary targets

Abstract

Time-of-flight spectra of ions from plasmas produced from planar, monoatomic targets of copper and tungsten, as well as binary targets of copper and tungsten, with two different stoichiometric compositions, have been obtained using a 125 mJ–5 ns, Nd : YAG laser, at a laser intensity of about 1010 W cm−2. Charge-resolved angular variations of the average velocity and kinetic energy of ions as well as the average integrated kinetic energy per ion from these plasmas are reported. The average degrees of ionization, summed over all the ions as well as over all the ions and neutrals, have been obtained as a function of angle with reference to the target-normal. It was observed that the significant energy transfer from the lighter to the heavier ions does take place, which is in good agreement with the results obtained from Monte Carlo simulations. Energy transfer among the ions of the same species, but with different degrees of ionization, has also been observed. Measurements on the average degree of ionization show the existence of a strong recombination mechanism indicating a definite role for it in the energy transfer. The effect of ion acceleration has been considered in detail and was found to be marginal in the present experiments. Supplementary results from monoatomic targets of aluminium and titanium and their binary targets with different stoichiometric compositions are presented.