Thursday, September 9, 2010

Lightning From Laser Beams

Lightning From Laser Beams

A team of European scientists has used high-power laser pulses to deliberately triggered electrical activity in thunderclouds for the first time, according to a paper in the latest issue of Optics Express.

At the top of South Baldy Peak in New Mexico during two passing thunderstorms, the researchers used ultrashort laser pulses from a femtosecond terawatt laser to create plasma filaments that could conduct electricity--akin to Benjamin Franklin's silk kite string. The laser beam diameter was 3 cm, and the energy per pulse was 270 mJ at a center wavelength of 800 nm. The 150 fs pulses were negatively chirped to 600 fs. No air-to-ground lightning was triggered because the filaments were too short-lived, but the laser pulses generated discharges in the thunderclouds themselves.By tweaking these laser pulses in the future, Kasparian thinks they should be able to create charged channels of molecules that act like conducting wires, and provide the lightning with a path to the ground.

In these experiments, the channels generated by the current laser didn't last long enough. The team estimates that they'll need to boost the power of the laser pulses ten-fold. The ability to generate laser-triggered strikes on-demand could make it easier for scientists to study lightning itself.Triggering lightning strikes is an important tool for basic and applied research because it enables researchers to study the mechanisms underlying lightning strikes. Moreover, triggered lightning strikes will allow engineers to evaluate and test the lightning-sensitivity of airplanes and critical infrastructure such as power lines.

"This was an important first step toward triggering lightning strikes with laser beams," says Jérôme Kasparian of the University of Lyon in France. "It was the first time we generated lighting precursors in a thundercloud." The next step of generating full-blown lightning strikes may come, he adds, after the team reprograms their lasers to use more sophisticated pulse sequences that will make longer-lived filaments to further conduct the lightning during storms.

Pulsed lasers represent a potentially very powerful technology for triggering lightning because they can form a large number of plasma filaments--ionized channels of molecules in the air that act like conducting wires extending into the thundercloud.
During the tests, the research team quantified the electrical
activity in the clouds after discharging laser pulses. Statistical analysis showed that their laser pulses indeed enhanced the electrical activity in the thundercloud where it was aimed. In effect they generated small local discharges located at the position of the plasma channels.

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