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HomeSciencePhysicsA Laser-Based “Lightning Rod”

A Laser-Based “Lightning Rod”

• Physics 16, 12

Experiments on a Swiss mountain show {that a} high-powered laser can affect the trajectory of lightning strikes—a step towards laser-based lightning safety.

TRUMPF/M. Stollberg

A laser fired into the sky near a communications tower has been shown to guide lightning strikes. To make the laser light visible in the photo, the researchers converted it from infrared to green wavelengths using a frequency-doubling device.

When Benjamin Franklin launched his well-known kite right into a stormy sky in 1752, he supplied a preferential path for the cost collected within the clouds to achieve the bottom. A twenty first century replace on Franklin’s kite is a laser fired up into the ambiance. Stationed on a Swiss mountain, researchers have proven that the beam from a high-powered laser gives a preferential path for lightning bolts [1]. Such a laser system might someday present lightning safety to delicate amenities, similar to airports, rocket launchpads, and wind farms.

The harm brought on by lightning—estimated to trigger billions of dollars of damage per year within the US—could be diminished by controlling the place the electrical discharge goes. “Currently, the only available protection against lightning is a classical Franklin lightning rod,” says Aurélien Houard, a member of the analysis crew from the École Polytechnique in Paris. These tall steel rods are good conductors that present a path of least resistance from the clouds to the bottom. But this safety is simply afforded to things inside a sure distance of the rod, given roughly by the rod’s peak. Building a better rod would defend a bigger space, however this resolution just isn’t all the time sensible.

“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. Unlike a steel construction, the laser “rod” might be turned on solely when the skies are threatening.

Laser-based lightning steering was first proposed in 1974, and several other experiments have confirmed the fundamental idea in a lab setting. However, demonstrating the system within the area has confirmed tougher. Some assessments had been unfortunate and by no means had a storm come shut sufficient to the laser. “Lightning is very unpredictable,” Houard says. “You may have to wait a very long time to see a strike.” And simply seeing one occasion isn’t sufficient: researchers have to construct up the statistics to ensure that the laser is having a noticeable impact.

To improve their possibilities, Houard and his colleagues carried out their laser experiment in some of the lightning-prone spots in Europe: Säntis Mountain, on the northeastern facet of Switzerland. This 2500-m-high (8000-ft) mountain is capped by a 30-story-tall telecommunications tower that’s struck by lightning about 100 occasions per yr. During the summer season of 2021, Houard and colleagues put in a car-sized terawatt laser on the mountain with the purpose of testing whether or not lightning paths might be guided by the laser mild.

In the start of their marketing campaign, the researchers relied on climate reviews to warn them of approaching thunderstorms, however the forecasts had been typically improper, and the crew missed some alternatives. “We decided to sleep on the mountain to be ready to start the laser if lightning came in the night,” Houard says. They additionally needed to alert the close by airport each time they deliberate to fireplace the laser, as there was a threat that the sunshine might harm the eyes of individuals in airplanes flying overhead.

Laser Lightning Rod challenge

This photo from July 24, 2021, shows a lightning strike that follows a straight trajectory in line with the laser path.

When the meteorological circumstances had been ripe, the crew aimed their laser into the sky and fired picosecond pulses at a repetition fee of 1 kHz. By focusing the infrared laser mild at some extent close to the highest of the tower, the researchers reached the depth obligatory to supply a nonlinear optical impact by which the laser mild divides up into a number of, skinny “filaments” that propagate with out spreading out (see Viewpoint: Air Waveguide from “Donut” Laser Beams). These high-intensity streams warmth the air, creating channels of ionized fuel, or “plasma,” that may be so long as 50 m. Such plasma channels are conducting, like a steel rod, so they’re anticipated to supply a preferential path for lightning.

Over the course of two months, the researchers operated their laser for a complete of six hours. During that point, the tower was struck by 16 lightning strikes. Based on visible and radio observations, the crew discovered that 4 of those strikes had been guided by the laser for a portion of their trajectories. Photos of one in every of these occasions clearly present a lightning bolt with a straight part that corresponded to the 50-meter plasma channel from the laser. The different three strikes had been measured with antennae on the mountain that report radio emissions from lightning discharges. The crew’s evaluation of those radio information revealed that, once more, these strikes had been aligned with the laser path.

The outcomes point out that the laser can affect the trail of lightning on its method to a continuously focused object (the tower). The subsequent step is to point out {that a} laser can defend extra delicate objects by “drawing fire” from the thunderclouds. “We would like to demonstrate that we can trigger lightning,” Houard says. For this utility, he imagines a extra highly effective laser, in a position to generate a plasma channel that extends 500 meters or extra into the sky. Such a tall laser rod might steer lightning away from a row of wind generators or a rocket readying for takeoff.

“It is a promising technology for lightning protection,” says lightning researcher Adonis Leal from New Mexico Tech. He questions how value efficient will probably be, provided that conventional lightning rods require no power to function. “We need more field campaigns such as this [experiment] to have reliable statistics on the efficiency of the laser system against the standard lightning-protection systems,” Leal says.

–Michael Schirber

Michael Schirber is a Corresponding Editor for Physics Magazine based mostly in Lyon, France.

References

  1. A. Houard et al., “Laser-guided lightning,” Nat. Photonics (2023).

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