Energy distribution of particles ejected by laser-generated aluminium plasma

A study of laser-generated plasma by visible laser ablation of aluminium, in high vacuum (3 × 10−7 mbar), by using 3 ns Nd:YAG laser radiation, is reported. Nanosecond pulsed ablation, at intensity of the order of 1010 W/cm2, gives an emission of neutral and charged particles. A special mass quadrupole spectrometer, operating in the 1–300 amu mass range, was used to analyse the energetic atomic emission produced by the laser ablation. Neutrals show typical Boltzmann distributions, directly correlated to the plasma temperature, while ions show Coulomb–Boltzmann-shifted distributions depending on their charge state. Surface profiles of the craters and microscopy investigations permitted to study the ablation threshold and the ablation yields. The multi-component structure of the plasma plume emission is investigated in terms of charge state, neutrals and ions temperature. A special regard is given to the study of the ion acceleration process occurring inside the plasma due to a high electrical field generated in the non-equilibrium plasma. The angular distributions of the neutral and ion particles are also presented and discussed.