CONFINING MEDIUM AND ABSORPTIVE OVERLAY - THEIR EFFECTS ON A LASER-INDUCED SHOCK-WAVE

In this paper the characteristics (stich as amplitude, width) of a las er-induced shock wave under confining conditions is studied. For engin eering applications, a physical study of this method is useful in ol d el to optimize this technique. We have first introduced a new pressure gauge - PVDF (polyvenyliden fluoride) gauge with short rise time and wide linear response range. Experimentally, by measuring the generated pressures under different confining materials, the relationship betwe en the pressures and the acoustic impedance of confining materials, is illustrated, which somewhat agrees with the theoretical calculation. We have also found that under confining conditions laser-induced shock waves persist longer than a laser pulse. Then, the effects of black p aint overlay (absorptive overlay) is studied. We experimentally point out that a black paint overlay placed before an irradiated target can greatly increase the generated pressure under any confining material i n our experiments for its beneficial effect on the plasma-generating p rocess. To our surprise, comparing the impulse (P-max.tau), which the shock wave induced under absorptive overlay executes on the target, to thar induced under no black paint overlay, the increase ratio is appr oximately equal. (C) 1998 Published by Elsevier Science Ltd. All right s reserved.