Lightning strikes about 40 million times in the U.S. each year. This natural phenomenon is terrifyingly random, and we rely mainly on lightning rods—a nearly 300-year-old technology—to deal with it. But researchers are finally working on a more 21st-century solution: laser beams.

Pioneered by Benjamin Franklin, the lightning rod works well to defend a building. But it only has a limited ability to protect larger swaths of land or sprawling facilities such as wind farms, airports and rocket launch pads. So a team of scientists has tried using a high-powered laser to guide lightning strikes atop a mountain in Switzerland. This “laser lightning rod” technique that could one day deflect strikes from important large-scale infrastructure. The results of the researchers’ new study were published this week in Nature Photonics.

“What they’ve done is very impressive,” says Jerry Moloney, an optical scientist at the University of Arizona, who was one of the early pioneers of this laser application but was not involved in the study. It’s “a very, very sophisticated setup.”

Lightning occurs when friction among water droplets creates a static electric charge within clouds, usually during storms. This electricity builds before being discharged in a giant spark, which can travel between the cloud and the ground, either upward or downward, following the path of least resistance. Regular lightning rods are made of conductive metal, and they provide a preferential point for the lightning to strike and then safely channel the charge around a building and into the ground. But metal is not the only way to attract lightning away from more vulnerable targets.

Laser lightning rod
The laser lightning rod fires 1,000 times a second. Credit: TRUMPF/Martin Stollberg

In the new experiment, a high-powered laser turns a column of air into an electrical conductor. When the laser is fired, the air molecules in the beam’s path are stripped of their electrons in a process called ionization. This transforms the air, which is normally insulating, into an attractive point for the lightning to hit—effectively creating a giant, temporary and controllable lightning rod in the sky above the area to be protected. Scientists had dreamed of building laser lightning rods for decades, but previous experiments had largely failed. Lasers that were available at the time could only pulse around 10 times per second, explains Aurélien Houard, a physicist at the École Polytechnique in France and first author of the study. That rate is too slow to keep an air column ionized. The new laser can fire 1,000 times per second, with each pulse lasting one trillionth of a second.

[Explore Scientific American’s coverage of laser lightning rods in the 1990s]

“You can burn stone if you want with this laser,” says Houard. The laser has an average power of one kilowatt (roughly the amount of electricity required to operate a large oven or refrigerator), says the paper’s senior author Jean-Pierre Wolf, a physicist at the University of Geneva.

The researchers tested their laser’s ability to draw lightning atop Säntis, a prominent peak in the Swiss Alps that was chosen because lightning often hits a telecommunication tower at its summit. There, during the summer of 2021, the team observed 16 lightning strikes—four of which occurred while the laser was powered on. And in all four cases, sensors—either a high-speed camera or a high-frequency electromagnetic wave detector—captured the lightning following the beam’s path. The results are preliminary for now, and the authors hope to fine-tune the technique with more data from future studies.

“The next step will be closer to the real-world applications,” Wolf says, “basically redoing this experiment, say, close to a launching pad or close to an airport.”

Lightning strikes at airports are an “ongoing issue,” and they not only delay flights but can also injure or kill employees and travelers, says Irene Miller, an assistant professor of aviation at Southern Illinois University, who was not involved in the new study. Most airports currently rely on early-warning systems to prevent planes from taxiing or landing when the risk of a strike is high.

It remains unclear how laser lightning rod technology might be adapted to this setting because even tiny lasers aimed at the sky are notoriously dangerous to pilots. During their recent mountaintop experiment, the researchers worked with aviation authorities to designate a no-fly zone around Säntis. One way to address such concerns could be to adjust the laser’s wavelength and power, and the study authors hope to explore that idea in future projects. For now, though, Benjamin Franklin’s innovation will have to do.