Laser-Driven Detonation Waves in Gases

Abstract

The plasma created by the output of a 2 to 10 J Q-switched ruby laser focused into air, argon, helium and hydrogen at pressures from 15 to 1000 psi has been photographically recorded during and after the laser heating pulse. The growth of the luminous plasma front during laser irradiation was in accordance with a prediction based on a radiatively supported detonation-wave model in which a Gaussian pulse shape was used for the instantaneous energy addition. With hydrogen at atmospheric pressure an appreciable fraction of the laser energy was transmitted. Consequently, the detonation-wave model had to include only partial absorption of the incident laser beam. This was done by using the inverse bremsstrahlung absorption coefficient and a constant depth of energy addition. The shock wave created by this sudden energy addition was observed by using a Schlieren system. The growth of the shock wave was not in accordance with that predicted by spherical-blast-wave theory. The shock-wave position from the initial point of breakdown varied as time from breakdown to the (0.20 ± 20%) power independent of gas species or operating condition.