Modeling of plasma dynamics at the air-water interface: Application to laser shock processing

The gas-dynamic expansion stage of the plasma at the air-water interface is studied numerically for the setup corresponding to the laser shock process ing of materials in the water-confined regime. The plasma is induced by a l aser radiation of the intensity range 4-17 GW/cm(2) at the 1.06 and 0.353 m um laser wavelength. A mathematical description of the plasma is performed in the frame of transient two-dimensional radiative gas dynamics, which inc orporates the system of gas-dynamic equations and the radiation transfer eq uation. The studies performed indicate that the plasma evolution significan tly depends on the laser wavelength. For the IR laser effect the expansion mechanism is the fast propagation of the ionization wave toward the laser s ource, and for the UV laser effect the laser supported detonation wave is f ormed. The plasma radiation contributes significantly to the redistribution of energy inside the plasma domain and, for the UV effect, forms the domai n of preionization ahead of the shock wave. In both cases the plasma become s opaque: for the IR effect it occurs over a very short period of time, 3-5 ns, while for the UV effect the process takes much longer. When the laser intensity is increased, the peak intensity and the duration of the transmit ted pulse tend to reach a saturation level. (C) 2001 American Institute of Physics.