Scientists announced Monday that they had used a laser beam to guide lightning for the first time, in the hopes that the technique will help protect against deadly bolts – and perhaps one day even trigger them.
Every year, lightning strikes between 40 and 120 times per second, killing over 4,000 people and causing billions of dollars in damage.
However, the most effective protection against these bolts from the sky is still the humble lightning rod, which was invented in 1749 by American polymath Benjamin Franklin.
For years, a group of scientists from six research institutions has been working on the same concept but replacing the simple metal pole with a far more sophisticated and precise laser.
They describe using a laser beam shot from the top of a Swiss mountain to guide a lightning bolt for more than 50 meters in a study published in the journal Nature Photonics.
"We wanted to give the first demonstration that the laser can have an influence on lightning — and it is easiest to guide it," said Aurelien Howard, the study's lead author and a physicist at the ENSTA Paris institute's applied optics laboratory.
However, "it would be even better if we could trigger lightning for future applications," Howard told AFP.
Lightning is caused by the discharge of static electricity that has accumulated in storm clouds or between clouds and the ground.
The laser beam generates plasma, which is made up of charged ions and electrons that heat the air. The air becomes "partially conductive, and thus a path preferred by lightning," according to Howard.
When scientists tested this theory in New Mexico in 2004, their laser failed to capture the lightning. According to Howard, the laser failed because it did not emit enough pulses per second for lightning, which brews in milliseconds.
It was also difficult to "predict where the lightning would strike," he said.
The scientists left little to chance in their most recent experiment. They carried a car-sized laser capable of firing a thousand pulses of light per second up the 2,500-meter Santis mountain in northeastern Switzerland.
A communications tower on the peak is struck by lightning approximately 100 times per year. After spending two years developing the powerful laser, it took several weeks to transport it in pieces via cable car.
Finally, the large containers that would house the telescope had to be dropped off by helicopter. The telescope directed the laser beam to a point about 150 meters above the ground, just above the top of the 124-meter tower. The beam begins with a diameter of 20 centimeters and narrows to a few centimeters at the top.
The scientists were able to photograph their beam driving a lightning bolt for 50 meters during a storm in the summer of 2021. Interferometric measurements revealed that three other strikes were also guided.
Most lightning is generated by precursors within clouds, but some can be generated from the ground if the electric field is strong enough.
"Once the ground is connected to the cloud, the current and power of a lightning bolt really become clear," Howard said.
One of these precursors is guided by the laser, making it "much faster than the others — and straighter," he says. "Before it lights up, it will be the first to connect to the cloud."
This means that, in theory, this technique could be used not only to repel lightning but also to initiate it. This could allow scientists to better protect strategic installations like airports or rocket launchpads by triggering strikes at their leisure.
In practice, this would necessitate a high conductivity in the laser's plasma, which scientists do not believe they have yet mastered.
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