Influence of nonlinear refraction on the dynamics and optimum performance of long optical discharges

The parameters and dynamics of breakdown are altered by the nonlinear refraction of the initiating beam by neutral and ionized particles in the path of the beam. The effects of nonlinear refraction are analyzed under various conditions, and it is shown that the thermal defocusing of the beam in the atmosphere prevents the formation of long optical discharges of 'beaded' structure whose behavior is dominated by heat conduction. However, collective effects at higher aerosol concentrations can give rise to a continuous plasma channel. The influence of thermal and Kerr nonlinearity on the dynamics of the focal region is analyzed for atmospheric discharges, and total internal reflection from the breakdown channel is also considered. The motion of the boundaries of the discharge channel is shown to be correlated with the polydisperse structure of the aerosol.