Investigation of gasdynamic processes and recoil impulse produced by optical breakdown of air near a target surface by radiation of an electron-beam-controlled CO$_2$ laser

An experimental investigation was made of gasdynamic processes resulting from the action of high-power (10$^9$ W) radiation of an electron-beam-controlled CO$_2$ laser on a metal target. The large area of the resultant optical breakdown (up to 27 cm$^2$), which appeared near the target surface, and the short duration of the laser pulses ($\tau_{1/2}=120$ 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 $q_{\text{th}}\lesssim5\times10^7$ W/cm$^2$ 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 dyn$\cdot$sec$\cdot$ J$^{-1}$, was measured and it was found that high values of the impulse could be obtained in large focusing spots.