Investigation of gasdynamic processes and recoil impulse produced by optical breakdown of air near a target surface by radiation of an electron-beam-controlled CO2laser

Abstract

An experimental investigation was made of gasdynamic processes resulting from the action of high-power (109 W) radiation of an electron-beam-controlled CO2 laser on a metal target. The large area of the resultant optical breakdown (up to 27 cm2), which appeared near the target surface, and the short duration of the laser pulses (τ1/2 = 120 nsec) made it possible to establish nearly one-dimensional gasdynamic motion. The development of a plasma jet under these conditions could be described by the model of a strong planar explosion. The breakdown threshold of air qth 5×107 W/cm2 decreased under the action of the radiation emitted from the plasma jet. The velocity of propagation of a wave of absorption of the laser radiation differed from the theoretical dependence predicted for an optical detonation wave. The ratio of the recoil impulse to the energy, 12.6 dynsecJ–1, was measured and it was found that high values of the impulse could be obtained in large focusing spots.