How to Bend Lightning with a Laser Beam

Controlling lightning is a monumental ambition, but that's just what a group of European scientists has done—albeit briefly and at enormous expense. By firing a laser into a Swiss thunderstorm, they gained a glimpse into how we might one day wield the gargantuan forces of the atmosphere.

"It's the first convincing evidence of how we can control lightning in a real-life environment."

"What they managed to do is impressive," said Matteo Clerici, a professor of photonics at the University of Glasgow who was not involved in the research. "It's the first convincing evidence of how we can control lightning in a real-life environment."

To do so, the team, whose work was recently published in Nature Photonics, created what's known as a laser filament. A filament arises from the self-focusing effect of the laser as it passes through air, which, like sunlight passing through a convex magnifying glass, concentrates its power. The energy becomes so intense that it "boils" the electrons off air molecules, or ionizes them, to create a plasma—a soup of superheated matter. That beam of hot plasma is called a filament.

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"When you have a very powerful laser, if you shoot it in the air, it will spontaneously form a filament," said study coordinator Aurélien Houard from the Laboratory of Applied Optics at École Polytechnique in Paris.

Filaments eject air molecules, a process which clears the path to funnel in lightning. "You create a lower-density channel," said Houard. "In this channel, the [lightning] charge can go faster than outside." The filament becomes a path of least resistance along which electricity will preferentially travel in the manner of a traditional metal lightning rod.

The ultimate goal, the researchers say, is to use the device to divert lightning away from sensitive areas like airports. Because of their far greater reach, lasers would be able to protect a much larger area than metal lightning rods.

The result is the culmination of more than 2 decades of research and experimentation.

To create filaments in the atmosphere, researchers use lasers that fire quick pulses that are less than 1 trillionth of a second in duration. It's the brevity that gives these lasers their power, simply because it's possible to cram more power into the peak of a shorter pulse than a continuous beam. "The idea of a short laser is that with a relatively small amount of energy, you can reach very high intensity," said Houard.

Previous attempts to control lightning failed in New Mexico in 2008 and Singapore in 2011. Houard believes that failure was, in part, because the lasers used could not pulse rapidly enough to maintain a low-density channel in the filament.

Those lasers could pulse only up to 10 times per second. But in Houard's study, the researchers teamed up with a German company, TRUMPF Scientific Lasers, to design a laser that could pulse 1,000 times per second. The device, the first of its kind ever made, cost more than 2 million euros to build. "The development of the laser was 2 years, then we had almost 2 years of testing," said Houard.

The 3-ton laser was installed next to a telecommunications tower at the top of Mount Säntis in Switzerland, a locality known for frequent lightning strikes. The scientists had to dismantle the machine, transport the pieces in a gondola, and deploy a large helicopter to position it on the mountain.

The installation took 3 months. "After so much time, effort, and money," said Houard, "there was a good chance to see absolutely nothing. It was quite a risky experiment."

After firing up the laser and pointing it toward the sky, however, the team's fears were soon allayed. Over a 2-month period, they recorded lightning bolts following the path of the laser four times. On one occasion, the sky was clear enough to allow cameras to capture a lightning bolt following the laser for around 50 meters (160 feet).

Despite the breakthrough, Houard concedes it will be a long time before lasers could replace conventional metal lightning rods. For starters, they need to address a number of safety issues. And beyond that, the device is incredibly expensive. "It would be mostly available to protect a very large infrastructure…like a launch pad or a nuclear power plant," Houard said.

The achievement could have far-reaching applications beyond protection from lightning. "The demonstration that it's possible to control such a large atmospheric event opens the door to other things," said Clerici.

For example, Houard is part of a team that is using laser filaments to reduce drag on supersonic aircraft, and colleagues, including Jean-Pierre Wolf, who was a contributor to this study, have discovered how laser filaments can punch holes in clouds, allowing for uninterrupted communication with satellites. Laser filaments can even create rain and snow.

"That's how science advances. Someone demonstrates the possibility, and once you have the possibility, there are going to be opportunities."

"It seems to me that this work is still quite foundational," said Miro Erkintalo, a laser physicist with the University of Auckland who was not involved in the study. "That's how science advances. Someone demonstrates the possibility, and once you have the possibility, there are going to be opportunities."

"I think the human mind is not particularly good at extrapolating the next decade," he said. "Most pioneering scientists are the ones that do things because they want to know if they can. The opportunities will come after."

—Bill Morris, Science Writer