GENERATION OF SHOCK-WAVES BY LASER-INDUCED PLASMA IN CONFINED GEOMETRY

Confined plasmas induced by neodynium glass laser at 1.06 mum and pulse width of 3 and 30 ns are studied. The metallic target is covered with a dielectric layer, glass or water, transparent to the laser radiation. Experimental measurements of the pressure induced by the plasma have been performed. For a certain range of laser power density these measurements agree particularly well with an analytical model. At high power densities (10 GW/cm2), the dielectric breakdown appears to be the main limiting process of the confining method. It is observed that this breakdown induces a saturation of the pressure. It is shown that the use of a short-rise-time laser pulse is the only way to reduce the effects of the breakdown and to obtain much higher-pressure shock waves. This is due to the dependence of the dielectric breakdown threshold on the laser pulse rise time.