Dynamics of plasma expansion in the pulsed laser material interaction (Q601056)

A pulse Nd: YAG laser with pulse duration of 5-10 ns, beam radius at focal point of 0.2-0.4 mm, wavelengths of 1064 nm, 532 nm, and 238 nm with linearly polarized radiation and Gaussian beam profile, was impacted on a thin foil of titanium metal for generating a plasma plume. Numerically, the above parameters were linked with the average kinetic energy of the electrons and ions in the laser-induced plasma. In the present model, electrons having higher velocities are assumed to escape from the plasma, so that a negatively charged sheath is formed around the plasma. It is seen from the present computations that the forward directed nature of the laser evaporation process results from the anisotropic expansion velocities associated with different species. These velocities are mainly controlled by the initial dimension of the expanding plasma. An attempt was undertaken to estimate the length of the plume at different ambient gas pressures using an adiabatic expansion model. The rate of the plasma expansion for various Ar\(^+\) ion energies was derived from numerical calculations. The numerical description of this plasma includes effects like collisional/radiative, excitation/de-excitation, and ionization/recombination processes involving multiples of energy levels with several ionization stages. Finally, based on a kinetic model, the plasma expansion rate across the laser beam axis was investigated.