Laser REMPI Triggering of an Air Spark Gap with Nanosecond Jitter

Abstract

A laser-triggering scheme for air spark gap switches was conceived and investigated for its potential to reduce shot-to-short time jitter. The scheme utilizes a pulsed ultraviolet laser of relatively low energy to generate resonant enhanced multi-photon ionization (REMPI) within the atmospheric air medium of the spark gap switch. With an applied voltage below the self-breakdown level, the laser-induced pre-ionization initiated avalanche breakdown within the gap and the subsequent triggering of the switch. This laser induced pre-ionization process relied solely on gas phase ionization and not surface effects, since the laser does not strike either electrode. This triggering scheme produced sub-nanosecond jitter with low enough laser power that it could be transmitted through fiber optics, which would be advantageous for multi-switch triggering of a high current pulse. The laser pre-ionization effects of space charge, electric field distribution, and active species within the gap were analyzed for their role in driving electron multiplication leading to avalanche breakdown below the self-breakdown voltage. Experimental results will be presented, including arc timing and statistical jitter measurements, as well as optical images and spectral analysis of the arc emission.