Don’t try this at home, but beaming a laser into the sky can prevent lightning strikes, according to a new study by a group of scientists who conducted laser experiments on the top of a Swiss mountain that is home to a large metal telecommunications tower. Physicist Aurelien Houart of the Applied Optics Laboratory of the French National Center for Scientific Research in Paris and his colleagues endured hours of storm activity to test whether the laser could deflect lightning strikes from critical infrastructure. Lightning strikes a telecommunications tower about 100 times a year.
This is similar to the number of lightning bolts striking planet Earth or cracking through clouds. every second Combined, these attacks can cause billions of dollars in damage to airports and launchpads, not to mention humans. Our best protection against lightning strikes is the Franklin rod, which is nothing more than a metal nail invented in the 18th century by Benjamin Franklin, who discovered that lightning strikes are zigzag electrical discharges. These rods are attached to metal cables that lower buildings and are fixed to the Earth, dissipating lightning energy.
Howard and his colleagues wanted to develop a better way to protect against lightning strikes by combating electricity with light.
“Although this area of research has been very active for over 20 years, this is the first field result to experimentally demonstrate laser-guided lightning,” they write in their published paper.
With the increase in extreme weather events caused by climate change on the radar, lightning protection is becoming more and more important. The experimental campaign took place on Sentis Mountain in northeastern Switzerland in the summer of 2021. Short, intense laser pulses were directed into the clouds during a series of thunderstorms and successfully deflected four lightning bolts upward from the top of the tower.
During those stormy periods when the laser was out, 12 more lightning struck the tower. Once, when the sky was clear enough to capture the event on two separate high-speed cameras, lightning struck 50 meters (164 feet) from the path of the laser. The sensors in the telecommunications tower also picked up electric fields and X-rays designed to detect lightning activity and verify its path, as you can see in the video replay below.
For an idea first proposed in 1974 and extensively tested in the lab, it’s exciting to see it finally working as intended in the real world. Several previous field tests, one in Mexico and another in Singapore, have found no evidence that lasers can deflect lightning strikes.
“These preliminary results should be confirmed by additional campaigns with new configurations,” Howard and colleagues write.
While the researchers are still figuring out why lasers worked in previous experiments and not in their tests, they have a few ideas. Howard and his colleagues’ laser used up to a thousand pulses per second, much faster than any other laser used, allowing the green beam to block any lightning precursors forming above the tower. But the recorded laser events only deflect positive lightning flashes, which are created by the positively charged cloud and create negatively charged “leaders”.
So how does it work?
As Howard and colleagues explain in their paper, a laser aimed at the sky changes the light-bending properties of the air, causing the laser pulse to compress and condense until it begins to ionize the air molecules. This process is called filamentation. Air molecules are rapidly heated in the path of the laser, absorbing its energy, and then ejected at supersonic speed. This leaves “long-life” channels of less dense air that offer a pathway for electrical discharges.
“At a high laser repetition rate, these long-lived charged oxygen molecules accumulate, preserving the memory of the laser path,” followed by lightning, the researchers write.
Experimental setup (left) and image (right) showing the filamentation zone above the tower. (Howard et al., Nature Photonics2023)
Meter-scale electrical discharges powered lasers in the lab, but this is the first time this technique has worked during a storm. The laser conditions were adjusted so that the beginning of the filamentous behavior started just above the tower.
“This work paves the way for new applications of ultrashort lasers in the atmosphere and is an important step forward in the development of laser lightning protection for airports, launchpads or large infrastructures,” Howard and colleagues said.
Source: Port Altele
