EXPANSION OF LASER-GENERATED PLUMES NEAR THE PLASMA IGNITION THRESHOLD

Expansion of laser-produced plumes on a solid-vacuum interface during and after the laser shot was investigated theoretically, incorporating several new features into our previous one-component one-dimensional hydrodynamic model. Time development of density, velocity, temperature, and pressure profiles was calculated at laser irradiances below and above the plasma ignition threshold. The estimated velocity of ions released from the plume was close to the measured values. The fast spreading of the blow-off material under the laser vaporization regime and the long lifetime of the relatively compact plasma core above the ignition threshold were predicted in agreement with experimental observations. Calculated surface recession due to evaporation provided a lower bound to the measured crater depth, whereas the calculated melt depth proved to be a realistic upper limit.