Gasdynamic estimates of the critical parameters of plasma formations accompanying laser breakdown due to aerosols in air

Numerical solutions are found of the secular differential equations of conservation of momentum and energy for a spherical variable mass of expanding air in a region trapped by a shock wave and described by effective values of the radial velocity, pressure, and temperature during the supply of laser radiation energy. The results obtained for various initial conditions indicate the existence of two branches: a rapidly damped solution and a relatively long-lived one characterizing the experimentally observed plasma formations. It is found that for λ =10.6 μ the threshold intensity for the occurrence of plasma formations decreases logarithmically with increasing initial radius R₀ and for R₀ ~0.01 cm it is ~50–100 MW/cm². An analytic expression is derived for the threshold breakdown intensity. It is established that the plasma formations are opaque to radiation, which possibly corresponds to their complex spatial configuration and structure on transition from the shock wave regime supported by the laser radiation to the detonation regime. The influence of plasma nonequilibrium and the role of the radial temperature and density profile are discussed.