![]() They also had to alert the nearby airport whenever they planned to fire the laser, as there was a risk that the light could damage the eyes of people in airplanes flying overhead. “We decided to sleep on the mountain to be ready to start the laser if lightning came in the night,” Houard says. In the beginning of their campaign, the researchers relied on weather reports to warn them of approaching thunderstorms, but the forecasts were often wrong, and the team missed some opportunities. During the summer of 2021, Houard and colleagues installed a car-sized terawatt laser on the mountain with the goal of testing whether lightning paths could be guided by the laser light. This 2500-m-high (8000-ft) mountain is capped by a 30-story-tall telecommunications tower that is struck by lightning about 100 times per year. To increase their chances, Houard and his colleagues performed their laser experiment in one of the most lightning-prone spots in Europe: Säntis Mountain, on the northeastern side of Switzerland. “You may have to wait a very long time to see a strike.” And just seeing one event isn’t enough: researchers need to build up the statistics to be sure that the laser is having a noticeable effect. ![]() “Lightning is very unpredictable,” Houard says. Some tests were unlucky and never had a storm come close enough to the laser. However, demonstrating the system in the field has proven more difficult. Laser-based lightning guidance was first proposed in 1974, and several experiments have confirmed the basic concept in a lab setting. Unlike a metal structure, the laser “rod” could be turned on only when the skies are threatening. “The idea of using a laser is to create an extension of a metal rod that could, in theory, be several hundreds of meters or a kilometer high,” Houard says. Building a higher rod would protect a larger area, but this solution is not always practical. But this protection is only afforded to objects within a certain distance of the rod, given roughly by the rod’s height. These tall metal rods are good conductors that provide a path of least resistance from the clouds to the ground. “Currently, the only available protection against lightning is a classical Franklin lightning rod,” says Aurélien Houard, a member of the research team from the École Polytechnique in Paris. The damage caused by lightning-estimated to cause billions of dollars of damage per year in the US-can be reduced by controlling where the electric discharge goes. Such a laser system could one day provide lightning protection to sensitive facilities, such as airports, rocket launchpads, and wind farms. Stationed on a Swiss mountain, researchers have shown that the beam from a high-powered laser provides a preferential path for lightning bolts. A 21st century update on Franklin’s kite is a laser fired up into the atmosphere. When Benjamin Franklin launched his famous kite into a stormy sky in 1752, he provided a preferential path for the charge accumulated in the clouds to reach the ground. ![]() To make the laser light visible in the photo, the researchers converted it from infrared to green wavelengths using a frequency-doubling device. ![]() Stollberg A laser fired into the sky near a communications tower has been shown to guide lightning strikes. ![]()
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