Don’t try this at home, but shining a laser in the sky might turn you away lightning according to a new study by a team of scientists who experimented with the lasers on a Swiss mountain where a large metal telecommunications tower stands.
Physicist Aurélien Houard from the Laboratory of Applied Optics at the French Center for Scientific Research in Paris and his colleagues survived hours of thunderstorm activity to test whether a laser can deflect lightning strikes away from critical infrastructure. The telecommunications tower is struck by lightning around 100 times a year.
This corresponds to the number of lightning bolts that strike planet Earth or crackle between clouds every second. Collectively, these strikes can cause billions of dollars in damage to airports and launch pads, not to mention people.
Our best protection against lightning strikes is a Franklin staffnothing more than one in the 18thth Century by Benjamin Franklin, who discovered lightning strikes Zig zag lightning bolts of electricity. These rods are connected to metal cables that run down buildings and are anchored into the ground to dissipate the lightning’s energy.
Houard and his colleagues wanted to develop better protection against lightning strikes and fight electricity with light.
“Although this research area has been very active for more than 20 years, this is the first field result experimentally demonstrating laser-guided flash,” they said to write in their published work.
Driven by an increase in extreme weather events climate change lightning protection is becoming increasingly important on the radar.
The trial campaign started in the summer of 2021 from Säntis in north-eastern Switzerland. Short, intense laser pulses were launched into the clouds during a series of thunderstorms, and four upward bolts of lightning were successfully deflected away from the top of the tower.
Another 12 lightning strikes hit the tower during those thunderstorm periods when the laser was inactive.
On one occasion, when the sky was clear enough to capture the action with two separate high-speed cameras, a bolt of lightning was recorded following the path of the laser for 50 meters (164 feet).
Sensors on the telecom tower also recorded the electric fields and X-rays generated to detect lightning activity and confirm its path, which you can see reconstructed in the video below.
frameborder=”0″ allow=”accelerometer; autoplay; write clipboard; encrypted media; gyroscope; picture in picture; web-share” allowfullscreen>
For an idea First presented in 1974 and extensively tested in the lab, it’s exciting to see it finally working as designed in the real world. Several previous field trials, one in Mexico and another in Singapore, had found no evidence that lasers can deflect lightning strikes.
“These preliminary results should be confirmed by further campaigns with new configurations”, to write Horde and colleagues.
While the researchers are still figuring out why the lasers worked in their experiments but not in previous experiments, they have some ideas. The Laser Houard and his colleagues used fire at up to a thousand pulses per second, much faster than other lasers used, allowing the green beam to intercept any precursor lightning that was forming over the tower.
But the recorded laser events only appeared to deflect positive flashes generated by a positively charged cloud, creating negatively charged upward “guides.”
How does it work?
As Houard and colleagues explain in their paper, the laser sent skyward changes the refractive properties of the air, causing the laser pulse to shrink and intensify until it begins to ionize air molecules. This process is called filamentation.
The air molecules are rapidly heated along the laser’s path, absorbing its energy, and then are ejected at supersonic speeds. This leaves “durable” channels of less dense air that provide a path for electrical discharges.
“At high laser repetition rates, these long-lived charged oxygen molecules accumulate and retain a memory of the laser path” followed by the flash, the researchers said to write.
Meters of electrical discharges have been directed by lasers in the lab, but the technique first worked during a thunderstorm. The laser conditions were set such that initiation of filament behavior started just above the top of the tower.
“This work paves the way for new atmospheric applications of ultrashort lasers and represents an important step in the development of laser-based lightning protection for airports, launch pads or large infrastructures,” say Houard and colleagues conclude.
The study was published in nature photonics.
