Plasma–laser characterization by electrostatic mass quadrupole analyzer

A study of laser ablation of different metals (aluminium, zinc, tantalum and lead), in vacuum, by using 3 ns Nd:YAG laser radiation, at 532 nm wavelength, is reported. Laser pulse, at intensities of the order of 109 W/cm2, produces high non-isotropic emission of neutrals and ionic species. Mass quadrupole spectrometry, associated to electrostatic ion deflection, allows estimation of the energy distributions of the emitted species within the plume as a function of the incident laser energy. Neutrals show typical Boltzmann distributions while ions show Coulomb–Boltzmann-shifted distributions. The plasma characterization is rationalized in terms of kinetic energies of ejected particles, ion, electron and neutral temperatures, ion charge states, and plasma density. A special regard is given to the parameters which regulate the plasma temperature: the boiling point, the electron density and the ionization potentials of the ablated elements. The ion acceleration processes occurring inside the plasma due to the high electrical field generated in the non-equilibrium plasma conditions are presented and discussed.