DYNAMICS OF ALUMINUM PLASMA PRODUCED BY A NITROGEN LASER

13 mJ laser pulses from a nitrogen laser were focused onto an aluminum target in air. The target surface was perpendicular to the axis of th e laser beam. A peak energy density of 1.3 J/cm2 and a power density o f 80 MW/cm2 were achieved with a laser pulse duration of 16 ns. The hi gh power density produced a transient plasma cloud that expanded explo sively into the surrounding atmosphere. An initial electron density of about 1 x 10(19) cm3 and an electron temperature of about 2 eV were d etermined by optical spectroscopy. The line of sight was parallel to t he surface and perpendicular to the laser beam axis. The height of the line of sight above the target surface was varied in order to gather data about the whole plasma cloud. In about 500 ns the plasma cloud ex pands to about 0.5 mm above the target surface, cools down to about 1. 2 eV and is tenfold reduced in electron density. The initial expansion velocity was determined to be about 2 km/s. The experimentally determ ined plasma parameters were input into numerical models of target heat ing and plasma expansion. The numerical results outrule the so called outflow model of plasma expansion and show reasonable agreement with a n effusion model. The observed discrepancies in observed and calculate d plasma parameters are attributed to the fact that the theoretical mo dels describe the plasma expansion in vacuum only.