State-to-state modeling of ultrashort laser-induced plasmas

At high argon pressure (105 Pa), the relaxation of the plasma takes place according to a rather low departure from LTE, as revealed by the thorough examination of the Boltzmann plots derived from the state-to-state models. This relaxation occurs at temperature higher for aluminum than for tungsten, but close to 10,000 K from 200 ns. Conversely, at low pressure (10 Pa), the extinction of the plasma is observed at ∼ 500 ns, just after a phase corresponding to significant departure from equilibrium. These results support the idea of the choice of short gate delays close to the laser pulse for the LIBS characterization of tungsten matrices in tokamak-like conditions.