Aluminum plasma produced by a nitrogen laser

Abstract

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 the laser beam. A peak energy density of 1.3 J/cm2 and a power density of 80 MW/cm2 were achieved with a laser pulse duration of 16ns. This high power density produced a transient plasma cloud that expanded explosively into the surrounding atmosphere. An initial electron density of about 1 × 1019 cm−3 and an electron temperature of about 2 eV were determined by optical spectroscopy. The line of sight was parallel to the 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 expands 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.