DYNAMICS OF LASER-ABLATED IRON IN NITROGEN ATMOSPHERE

Fast photography with a framing streak camera is applied to investigat e the dynamics of ablated Fe particles by a pulsed excimer laser when a nitrogen atmosphere is present. Two stages of expansion are found in the generated plume. The first one starts just after the laser irradi ation where the hemispherical and unidirectional plumes are found simu ltaneously. The dynamics of the unidirectional plume is described by a drag model for 300 ns. The second stage occurs at 300 ns, and the uni directional plume expands again in agreement with a delayed blast wave model. The thickness distribution of the deposited Fe-N film is well correlated with the change in the plume geometry, then with the nitrog en pressure.