Scientists have controlled lightning with lasers for the first time in the field, according to a demonstration carried out during severe storms on top of a Swiss mountain.
The feat, which involved firing powerful laser pulses at thunderstorm clouds over several months last year, paves the way for laser-based lightning protection systems at airports, launch pads and tall buildings.
“Metal rods are used almost everywhere for lightning protection, but the area they can protect is limited to a few meters or tens of meters,” said Aurelien Howard, a physicist at Ecole Politechnikue in Palaiseau. “We hope to extend that protection to a few hundred meters if we have enough energy in the laser.”
Lightning bolts are huge electrical discharges that usually spark more than two to three miles. The charge carried in the bolt is so intense that it reaches 30,000C, about five times hotter than the surface of the sun. More than a billion bolts hit the Earth each year, causing thousands of deaths, 10 times more injuries, and damage running into the tens of billions of dollars.
Traditional lightning rods date back to Benjamin Franklin chasing thunderstorms on horseback before his famous kite experiment in 1752. But more recently, scientists have looked for other ways to protect buildings and structures from damaging lightning strikes.
Writing in the journal Nature Photonics, Howard and his colleagues in Switzerland describe how they drove a powerful laser to the top of Mount Sentis in northeastern Switzerland and parked it near a 124-meter-tall telecommunications tower that was struck by lightning about 100 times a day. years.
The scientists waited for the storms to gather and between July and September last year they fired fast laser pulses at thunderclouds for a total of more than six hours. Instruments set up to record the lightning strike showed that during the experiments, the laser redirected the flow of four discharges upwards.
Only one strike, on July 21, occurred in clear enough conditions for researchers to record the lightning’s path from two directions using high-speed cameras several kilometers away. The video shows that the lightning followed the laser path for about 50 meters, suggesting that the pulses helped steer the strike.
A laser redirects lightning by creating an easier path for the electrical discharge to flow. When the laser pulses are fired into the sky, the change in the refractive index of the air causes them to gather and become so intense that they ionize the air molecules around them. This leads to a long chain of what researchers call filaments in the sky, where air molecules are rapidly heated and raced at supersonic speeds, leaving behind 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.
The laser is powerful enough to pose a danger to the eyes of pilots flying over it, and air traffic was closed over the test site during the experiments. But scientists believe the technology could still be useful, as launch pads and airports often have designated areas where no-fly restrictions apply. “It’s important to consider this aspect of security,” Howard said.
More powerful lasers operating at different wavelengths could guide lightning over greater distances, he added, and even initiate lightning before it becomes a threat. “You avoid it going somewhere else where you can’t control it,” Howard said.
“The cost of a laser system is very high compared to the cost of a simple rod,” said Professor Manu Haddad, director of the Morgan-Botti Lightning Laboratory at Cardiff University. “However, lasers may be a more reliable way to direct lightning discharges, and this may be important for lightning protection of critical ground installations and equipment.”