Metallic plasma production by laser ablation

Laser production of plasma at the surface of a metallic target was modeled. The mechanism of plasma production comprises several common phenomena at the target surface, at the plasma-target interface and in the plasma expansion region. Atom vaporization and electron emission due to target heating by high intensity laser radiation and the plasma were considered. The heat flux from the plasma is convected by ions and returned electrons. At the plasma-target interface, an electrical sheath appears in which all charged particles are accelerated. The accelerated electron emission beam conveys energy into the plasma and together with partial absorption of the laser energy heats the plasma electrons. A mathematical model was formulated, which describes the phenomena in the solid target, space charge sheath, electron beam relaxation region, plasma expansion region and the Knudsen layer, where the vapor flux from the target was formed. The model allows determination of the target temperature, plasma density and plasma temperature, potential drop in the sheath and electrical field at the target surface, electron and ion current density, the rate of target vaporization, vapor degree of ionization and plasma velocity for the model was applied to an example of an Al target, with laser pulse durations of 1 ns, 10, 103 and 10 ms and laser power density of qL=10-3-1 GW/cm2. The plasma parameters and rate of target ablation were compared with the experimental data.