Scientists direct lightning with lasers for the first time | Physics

Scientists have conducted lightning with lasers in the field for the first time, according to a demonstration conducted during heavy storms atop a Swiss mountain.

The feat, which involved firing powerful laser pulses at thunder clouds for several months last year, paves the way for laser-based lightning protection systems at airports, airstrips and tall buildings.

“Metal rods are used almost everywhere to protect against lightning, but the area they can protect is limited to a few meters or tens of meters,” said Aurélien Houard, a physicist at École Polytechnique in Palaiseau. “The hope is to extend this protection to a few hundred meters if we have enough energy in the laser.”

Lightning bolts are huge electrical discharges that usually send sparks over two to three miles. The charge carried in a screw is so intense that it reaches 30,000C, about five times hotter than the surface of the sun. More than a billion bolts strike the Earth each year, causing thousands of deaths, 10 times as many injuries and tens of billions of dollars in damage.

The traditional lightning rod dates back to Benjamin Franklin, who used to ride out storms on horseback before his famous kite experiment in 1752. But in more recent times, scientists have looked for other ways to protect buildings and objects from damaging strikes.

Writing in the journal Nature Photonics, Houard and colleagues from Switzerland describe how they carried a powerful laser to the top of Mount Säntis in northeastern Switzerland and parked it next to a 124m-tall telecommunications tower that is struck by lightning for about 100 times a day. year.

The scientists waited for the storms to gather, and between July and September of last year, they fired fast laser pulses at the thunderclouds for a total of more than six hours. Instruments installed to record lightning strikes showed that the laser deflected the course of four lightning discharges upwards during the experiments.

A single strike, on July 21, occurred in conditions clear enough for researchers to film the lightning’s path from two directions using high-speed cameras several kilometers away. The recordings show that the flash followed the path of the laser for about 50 meters, suggesting that the pulses helped direct the strike.

The laser deflects the lightning creating an easier path for the electrical discharge to flow down. When the laser pulses are fired into the sky, a change in the refractive index of the air causes them to shrink and become so intense that they ionize the air molecules around them. This leads to a long chain of what researchers call filaments across the sky, where air molecules heat up quickly and blow away at supersonic speeds, leaving a channel of low-density, ionized air. These channels, which last milliseconds, are more electrically conductive than the surrounding air and thus form an easier path for lightning to follow.

The laser is powerful enough to pose a risk to the eyes of pilots flying overhead, and air traffic was closed over the test site during the experiments. But scientists believe the technology could still be useful because airstrips and airports often have designated areas where no-fly restrictions apply. “It’s important to consider this aspect of safety,” Houard said.

More powerful lasers operating at different wavelengths could guide lightning over longer distances, he added, and even trigger lightning before it becomes a threat. “You avoid it going somewhere else where you can’t control it,” Houard said.

“The cost of the laser system is very high compared to that of a single rod,” said Professor Manu Haddad, director of the Morgan-Botti Lightning Laboratory at Cardiff University. “However, lasers could be a more reliable way to direct the lightning discharge, and this can be important for lightning protection of critical ground-based facilities and equipment.”

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