The dynamics of air breakdown initiated by a particle in a laser beam

Abstract

An experimental study was made of air breakdown induced by a single 50-μm particle at the focus of a 5-J pulsed 10.6-μm laser beam. The breakdown thresholds for 50-μm carbon and NaCl particles were ?5×107 and 8×107 W/cm2. The dynamics of plasma formation were studied with an image-converter camera. At low intensities the plasma grew as an axisymmetric volume surrounding the particle. At higher intensities the plasma formed as a thin disk which propagated towards the laser. The growth rates were measured as a function of beam intensity. The transmitted laser energy was measured as a function of beam parameters and compared to an idealized dynamics model.