Mechanism of optical breakdown of a gas containing an easily ionizable substance as an impurity

A theoretical analysis is made of the process of optical breakdown in gases containing an easily ionizable substance as an impurity. It is shown that the breakdown may take place in two stages. As usual, the initial stage is an electron avalanche in the impurity, which ends by complete ionization of the impurity. In the second stage, when the gas temperature has reached a critical value, an ionization-thermal explosion of the gas takes place. An analysis is made of the experimental observations of the phenomenon of “self-ignition” of an optical discharge near a solid surface.