A laser that redirects lightning could be used to protect critical buildings during storms.
When an electric charge builds up in clouds, lightning can either propagate downwards, from clouds to the ground, or upwards from tall objects towards the clouds. Regardless of the lightning鈥檚 direction of travel, conductors such as metal rods are generally used to redirect the electric current away from vulnerable targets and into the ground.
Efforts to control lightning have involved firing rockets with wires attached into clouds to force them to discharge their lightning. But in the 1990s, people started to experiment with using lasers to redirect the current instead. While the technique proved successful with artificial lightning, it had never been demonstrated in a real storm.
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Now, at the University of Geneva, Switzerland, and his colleagues have fired a series of very short, high-powered laser pulses from a 124-metre tower equipped with a standard metal lightning rod, on Switzerland鈥檚 S盲ntis mountain.
The terawatt laser was fired upwards during thunderstorms over a three-month period, for a total of 6.3 hours of operation time. During that period, the tower was hit by at least 16 lightning flashes, which propagated up to the clouds from the tower. Wolf and his team recorded the paths of four streaks of lightning heading up from the metal rod, along the path of the pulsing laser, using high-speed cameras, interferometry and X-ray detectors.
鈥淪cientifically, I think it鈥檚 really interesting,鈥� says at the University of Reading, UK. 鈥淚t will help us understand the processes by which lightning finds its way to ground.鈥�
Theoretically, the laser directs the lightning using filamentation, says Scott, which is when a laser pulse leaves long channels of ionised, low-density air for the lightning to travel along. This could be replicating the effect of cosmic rays in the atmosphere, which are thought to help seed conductive pathways for lightning to reach the ground, says Scott.
Lasers could potentially be used when a storm is brewing to trigger lightning at a safe distance from anything that needs protecting by having the current follow the path of the laser.
However, wielding a high-powered laser to fend off lightning would require careful safety assessments, adds Scott, and could be unsuitable for built-up areas.
at the University of Florida says the demonstration is important and the first of its kind, but that it isn鈥檛 certain to what extent the laser is guiding the lightning bolt.
鈥淚t is not clear whether the laser interaction produces a full triggered lightning, as in the rocket-and-wire case, which would be spectacular, or whether the laser interaction just serves to straighten out 100 metres of natural upward lightning from the tower,鈥� says Uman. 鈥淐learly, more experiments are needed, but the [experiment] is an excellent start.鈥�
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