Laser lures lightning away

一个“虚拟避雷针”,可以引导闪电to strike a safe conductor has been demonstrated successfully by researchers in France. Writing in Nature Photonics, Paris’ Ecole Polytechnique scientist Aurélien Houard, has built one of the world’s most powerful lasers. Fired into the air during an electrical storm, it can ionise the atmosphere to produce a short-lived conductive thread through the air that effectively extends the working height of a lightning conductor and lures the lightning bolt to that target. It’s just a proof of principle at this stage, but the long term vision is to use devices like this to protect high value and sensitive sites, like airports or power systems, where lightning strikes can prove highly disruptive…

Aurelien - A lightning rod will concentrate the electric field by bending the electric field around it. But the action of this lightning rod is limited in space. So if you want to protect a very large area, for example, an airport or a power plant, you would need a higher lightning rod. The the idea for our technology is to be able to generate virtually this conductive lightning rod with the laser and hopefully, over several hundreds of kilometres be able to protect.

Chris - So in essence then the laser effectively turns a patch of atmosphere that it goes through into a surrogate extension of that lightning rod for a while, so that you are more likely to make a path of the lightning there rather than in another patch of sky.

Aurelien - Yes, exactly.

Chris - And how does the laser do that? What's it doing to the atmosphere that makes you have an atmospheric lightning rod?

Aurelien - The effect of this laser, which is particularly intense, is that when it's propagatiing the atmosphere it has enough intensity to detach electrons from the molecule. You create what we call plasma, a bit similar to a conductor, and this effect will create a conducting path for any electricity.

Chris - And did your experiment suggest that this can work?

Aurelien - Yes, exactly. Our experiment demonstrated for the first time that this conducting path created by the laser is powerful enough to guide the lightning over more than 50 metres. So it is the first time that people have managed to have an influence on the real lightning with just light and, demonstrated that, on a scale of almost a hundred meteres, you can now control the path of the lightning.

Chris - How did you actually do it? And where?

Aurelien - First we had to develop a specific laser with a lot of power. It is the biggest one in this category. It took us two years to develop this laser, and then one year to test. And finally we installed everything in Switzerland on top of a mountain. And we choose this specific location, which is called Mount Santis because it's one of the places in Europe with the highest number of lightning strikes. And that was successful because we managed to observe several events where we had all the diagnostics working perfectly and the laser generating the conducting path.

Chris - Just speculating about how this might be used in the future in some way: you'd have to fire the laser whenever there were the correct conditions for a potential strike. You just put the lasers on and they would provide this thread through the clouds and the atmosphere towards the lightning conductor that you wanted to be the target. And then you just hope that when lightning does discharge, it's going to come down the pathway, the conduit that you've created with the laser, and you do that whenever you think there's a high risk of a storm strike.

Aurelien - Yes, exactly. You can use a detector to measure the electric field on the ground, and when the value is high enough, you know that the clouds have a possibility to generate lightning, and then you can start to shoot your laser and wait for lightning to develop eventually. If the laser is powerful enough, you could even imagine that it could trigger the lightning before it appears.

Chris - Presumably it's going to cost quite a bit to run a laser of this sort of power. Could you make it self powering by grabbing enough energy from the lightning and tapping it off to then help to offset the power bill for running the laser?

Aurelien - Yeah, that would be a nice idea, to collect the energy from the lightning. But the difficulty actually is that you receive a lot of current in one shot and there is no battery that can support such a large current and that could store it to reuse it later. So, for the moment, there is no real project to harvest the lightning electricity since it's not doable for real application.