PROPAGATION OF A LASER-SUPPORTED DETONATION-WAVE

Experiments were performed in order to determine the aerodynamic values of the gas velocity, pressure and temperature which are produced by a radiation driven wave in air. The wave is initiated on a plane target surface area of 2 cm2 by the focussed 10.6 μ laser light energy (maximum of 280 joules in 3 μ sec). The resulting flux intensity which was approximately constant during 1 μ sec of the pulse, varied between 107 and 1.5 × 108 W/cm2 as related to the emitted laser energy. Comparison of the incident and transmitted pulses permitted the determination of the deposited light energy on the target surface and of the characteristic time for plasma formation. The plasma front propagation velocity was measured by a streak camera. A piezoelectric gage of a relatively small diameter compared to the impact cross-section measured the pressure applied to the target during the interaction. The temperature was deduced from an analysis of the plasma spectra emission which was measured at different distances from the target. From measurements of laser line absorption at 488 nm and 633 nm the plasma density was estimated. The time between the beginning of the laser pulse and the beginning of the front propagation in air was found to be about 100 ns. This time did not seem to depend upon the target material. Considering that the cross-section was sufficiently large, these measurements give the necessary information to illustrate that, for the range of laser flux considered, a one-dimensional model of a detonation wave correctly describes the aerodynamic flow during the time of laser-light energy deposition. © 1979.