Laser initiated spark development in an air gap

Abstract

Spark development is studied by 20-nsec image converter photography. A diffuse and transparent prechannel bridges the gap from the top of the metal vapor jet, which has counterelectrode potential. The prechannel cuts off the development of the cone shaped jet with increasing gap voltage. The final breakdown is initiated by a z-axis, laser induced filament, which expands into the prechannel volume within ≲10 nsec. This interval represents the final high current thermalization phase of the breakdown. Thermal expansion of the initial spark channel (Braginskii) follows.