Role of quantum effects in the breakdown of gases by laser radiation

A theoretical investigation is made of the development of avalanche ionization of a gas by an optical pulse. The nonmonotonic dependence of the optical breakdown threshold on the radiation frequency is shown to be related to the quantum nature of changes in the electron energy in the field of an optical wave. A steep fall of the threshold in the ultraviolet range is due to a high probability of penetration of an electron to an ionization region as a result of a quantum jump across the zone representing losses due to excitation of the atomic levels. This theory is compared with experimental results on the breakdown of rare gases. An investigation is reported of the optical breakdown in the presence of lf, microwave, or static fields. It is shown that the reduction in the optical breakdown threshold under these conditions is due to quantum effects.