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

The potential ability of lasers to control lightning can be improved by using a train of pulses with sub-millisecond separations [1-2]. 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 [3-4]. 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. \newline References \newline [1] M.Yamaura, et al: J.Appl.Phys.\textbf{ 95}, 6007 (2004). \newline [2] M.Yamaura,et al : Appl.Phys Lett. \textbf{86} 131502 (2005). \newline [3] M.Yamaura: J.Appl.Phys.\textbf{98} 043101 (2005) \newline [4] M.Yamaura,et al : Appl.Phys Lett. \textbf{88 }to be appeared in June (2006)