Lightning on demand, drawing down a bolt of lightning for performing scientific studies, is usually done by firing a rocket into an overhead cloud. The rocket spools out a long wire, providing a conducting path between the charged-up cloud and the earth below. Soon this might be done using laser pulses.
A team of French and German scientists has performed experiments in the lab in which a laser beam ionizes air molecules between an artificial thunderhead (a high voltage electrode) with another electrode, the equivalent of “earth” (a grounded electrode), several meters away.
The experiment is unique in that it can trigger megavolt discharges across self-guided plasma filaments in air generated by laser pulses. (Here are the potent characteristics of natural lightning: peak power of ten megawatts, peak voltage of 100 MV, peak currents of tens of kilo-amps.) One of the lab results is the surprising discovery that rain does not much perturb the triggering or guiding of the discharge process.
Next the team will perform open-air lightning experiments. The aim of this work will be to obtain the ability to trigger lightning before it occurs naturally at sensitive sites such as airports or electrical substations. (Ackermann et al., Applied Physics Letters, 6 December 2004; contact Jerome Kasparian, Universite Lyon, jkaspari@lasim.univ-lyon1.fr