the transition of a substance to the state of a strongly ionized hot gas—a plasma—under the action of an electromagnetic field of optical frequency. Such laser-induced breakdown is similar to microwave breakdown and was first observed in 1963 when the radiation of a powerful pulsed ruby laser was focused in air.
When the phenomenon occurs, a spark arises at the focus of the lens; the observer perceives a bright flash accompanied by a loud sound. For gases, the values of the light flux intensity in the laser beam that are needed to reach the breakdown threshold are ∼ 109-1011 watts/cm2, corresponding to an electric field strength of 106-107 volts/cm. The observation of laser sparks stimulated research on the propagation and maintenance of a gas discharge by a laser beam for the purpose of creating optical plasmatrons (seeLASER RADIATION, EFFECTS OF).
Laser sparks are also observed in condensed media when powerful laser radiation is propagated in such media. Laser sparks can cause damage to materials and optical parts in laser devices.
REFERENCESRaizer, Iu. P. Lazernaia iskra i rasprostranenie razriadov. Moscow, 1974.
MacDonald, A. Sverkhvysokochastotnyiproboi v gazakh. Moscow, 1969. (Translated from English.)
V. B. FEDOROV