Laser lightning rod

With a peak power of 10 MW, a peak voltage of 100 MV, and peak currents of tens of kiloamps, natural lightning is notoriously unpredictable. Producing lightning on demand—for performing scientific studies or protecting sensitive sites—is usually done by firing a rocket into an overhead cloud. The rocket spools out a long wire, which provides a conducting path between the charged cloud and the grounded Earth. Soon, however, ultrashort laser pulses might accomplish the same thing. A team of scientists from France and Germany has used 170-fs laser pulses in the lab to generate self-guided plasma filaments that triggered and guided high-voltage discharges across a 1.2-m gap, even with a dense rain cloud in the experimental chamber, as shown here. Compared to dry air, a cloud’s presence reduced the discharge probability for a given laser shot. But according to the researchers, with many laser-shot repetitions per second, the real-world effectiveness of the technique should be undiminished. Next, the team will perform open-air lightning experiments. (R. Ackermann et al., Appl. Phys. Lett. 85, 5781, 2004 http://dx.doi.org/10.1063/1.1829165 .)