Theory of the Ionization of Gases by Laser Beams

Abstract

The ionization of gases by intense pulsed laser beams is discussed. In particular, the production of ions and electrons by direct multiple absorption of photons is considered in simple terms and it is concluded that the experimentally observed gas breakdown is probably initiated by this process, but that the subsequent growth of electron population is governed by some other process, such as inverse bremsstrahlung, or the acceleration of electrons in the oscillatory field. The theory predicts that the variation of threshold photon intensity for breakdown of a gas should exhibit almost pressure-independent low and high limits, that the range of intensities between these limits should be approximately $\frac{{\left({10}^{13}\right)}^1}{{}_{}{}^N{}_{}{}^{}\nu }$, where $N_{\nu }$ is the number of photons required to raise the atom to its lowest excited state, and that the threshold flux density will vary with change of focal volume as $V^{-\frac{1}{N_{\nu }}}$.