Density and lifetime evaluation of weakly ionized plasma for lasertriggered lightning by means of laser absorption

Summary form only given. The potential ability of lasers to control lightning can be improved by using a train of pulses with sub-millisecond separations. Laser-triggered experiments in a small scale (10 mm gap) atmospheric discharge facility show that the triggering is dramatically enhanced when a five-pulse train of sub-Joule energy is used instead of a single pulse. This effect increases rapidly as the pulse interval is reduced. In order to evaluate the trigger effect quantitatively, the plasma density produced by a pulsed KrF excimer laser with high repetition rate of kHz order was measured by means of laser absorption. It appears that at a sub-millisecond pulse interval, sufficient positive and negative ions survive in subsequent pulses, thus enabling easy deionization. Hence, significant plasma build-up occurs from one pulse to the next. However, this persistence of ions would appear to imply that the rate of recombination (effectively a charge transfer between ions) is considerably lower than previously believed. The density measurement of weakly ionized plasma of the order of 10¹³ cm^-3 is applied for by means of laser absorption will also be discussed