Confining medium and absorptive overlay: Their effects on a laser-induced shock wave

In this paper the characteristics (stich as amplitude, width) of a laser-induced shock wave under confining conditions is studied. For engineering applications, a physical study of this method is useful in ol del 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 between 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 paint 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 in our experiments for its beneficial effect on the plasma-generating process. 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 approximately equal. (C) 1998 Published by Elsevier Science Ltd. All rights reserved.