Laser-guided lightning rod takes Ben Franklin’s invention to new heights

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Benjamin Franklin is credited with inventing the lightning rod, and for some 270 years it has remained the main tool for protecting buildings from destructive and potentially deadly thunderbolts. But now an ambitious experiment on a Swiss mountaintop has demonstrated that a laser beam can also help guide the path of lightning, extending the effectiveness of the Franklin rod high into the sky.

Lightning rods are made of metal, which conducts electricity much better than the surrounding air and helps guide lightning to the ground harmlessly. The protection offered by a traditional lightning rod covers an area with a radius roughly equal to the height of the rod.

The idea behind laser-guided lightning is to extend that protective area by making the lightning rod function as if it soared hundreds of feet taller, to heights that would be impractical and costly for a physical object.

The report, published Monday in the journal Nature Photonics, claims that powerful lasers could be deployed to help protect sensitive sites such as airports and launchpads.

Decades of laser experiments in laboratories previously showed that, in principle, lasers would be useful for taming the heavens. The report states that this is the first time the concept has been demonstrated in the real world amid an actual tempest.

Joseph Dwyer, a University of New Hampshire physicist who was not part of the research and has expertise in the physics of lightning, praised the report as “a big step forward.”

“People have been trying to do things like this with lasers for a long time,” Dwyer said. “Using lasers instead of a lightning rod, or using lasers to trigger or steer lightning, is a fascinating idea. It seems like a no-brainer but it turns out to be really hard to do.”

The experiment was performed on Säntis Mountain, in northeastern Switzerland. A 407-foot (124-meter) communications tower there, equipped with a lightning rod, is struck roughly a hundred times a year.

The researchers positioned a car-size device for generating a high-power, rapid-fire laser next to the communications tower and fired pulses into the sky during stormy weather. The laser created not only a beam of light, but also a channel of thinned-out air that beckoned the lightning.

As the laser fired, air molecules absorbed and expelled the laser energy very rapidly, leaving behind long-lived channels of heated air with reduced density. Those channels functioned as a preferred path for the lightning.

Over a cumulative six hours during a multiweek stretch of summer storms, the atmospheric channel created by the laser diverted four lightning bolts.

A rendering shows what happened in 2021 when scientists used a laser as a lightning rod. (Video: Scientify – UNIGE)

High-speed cameras captured images from two different angles of one of the lightning strikes. They obviously show the bolt diving into the laser channel and traveling along it for more than 160 feet.

Despite the successful test, laser-based lightning rods are not about to pop up at Home Depot.

“It’s a technology that can be used to protect very large structures,” the study’s lead author, Aurélien Houard of École Polytechnique in Paris, told The Washington Post. “It’s quite expensive. It costs about 1 million euros. You would not use it for any small protection. You would use it for an airport, where you have a lot of planes, or a launching pad for rockets.”

The laser used in the experiment is not the kind of thing a professor would use during a PowerPoint presentation. It produced up to a thousand pulses per second. That unusually rapid firing of the laser was crucial to making this experiment succeed when previous efforts did not, Howard said.

The researchers believe the rapidity of those pulses produced the atmospheric changes in the nick of time to create a column of hot air that favors electric discharge. “The lightning apparition can be very fast,” Howard said. The laser’s rapid pulsing improves the odds of snatching the lightning bolt into the artificially created atmospheric channel.

Lightning is an electrostatic discharge that can take many forms — sometimes descending from the cloud to the ground, sometimes rising from the surface, sometimes meandering within a single cloud or jumping from one cloud to another. It’s dangerous. Upward of 4,000 lightning deaths are confirmed annually worldwide, according to the Nature Photonics report.

Jean-Pierre Wolf, a physicist at the University of Geneva and leader of the experiment, said in an email that in the United States alone, lightning damage costs more than $3 billion annually.

Lightning strikes also present a danger to electronics, including the sensitive equipment on commercial planes and space-bound rockets.

Launchpads typically deploy multiple lightning rods in a perimeter around the launch tower. But lightning storms remain a concern for NASA and the military, which face costly delays when rockets have to be pulled back from the pad to lower the risks of a damaging thunderbolt.

The Switzerland experiment may have demonstrated the principle of laser-guided lightning, “but we’re a long ways away from having the technology to keep everybody safe from lightning,” said Dwyer, the University of New Hampshire physicist.

He pointed out that for most people there is a simple, traditional, non-technological way to lower lightning risk: “If you hear thunder, go inside.”

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