Scientists use laser to steer lightning bolts

The demonstration was considered the first time that humans have been able to guide lightning with lasers, a technology that could help protect wider areas against dangerous strikes.  

The Laser Lightning Rod (LLR) is a new laser system with an average power of 1kW, pulsing about 1,000 times per second while unleashing one joule of energy per pulse.

To test the technology, a team of scientists from six research institutions set up the LLR on the summit of Säntis, in the Swiss Alps, near a 124m-high telecoms tower that is struck by lightning about 100 times a year. Between June and September 2021, the researchers beamed a laser into the clouds, aiming to create a path of least resistance for the electricity to flow through.

The system was used during four lightning strikes over the course of the summer, in which it was able to bend the bolt successfully and divert its path over 50 metres.  

Lightning bolts are huge electrical discharges that typically spark over two to three miles. Their charges can reach temperatures of as high as 30,000ºC, about five times hotter than the surface of the Sun.

“When very high power laser pulses are emitted into the atmosphere, filaments of very intense light form inside the beam,” said Jean-Pierre Wolf, one of the team’s researchers. “These filaments ionise the molecules of nitrogen and oxygen present in the air, which then release free electrons to move. This ionised air, called ‘plasma’, becomes an electrical conductor.

“We found, from the first laser lightning event, that the discharge could follow the beam for almost 60m before reaching the tower, thus increasing the radius of the protection surface from 120m to 180m. 

At the moment, more than a billion bolts strike Earth each year, causing over 4,000 deaths, 10 times as many injuries, and damage that runs into tens of billions of dollars.

Although previous research has pointed out the potential benefits of using laser technologies instead, this is reportedly the first time that this use case has been put to the test. 

“We wanted to give the first demonstration that the laser can have an influence on lightning – and it is simplest to guide it,” said Aurelien Houard, the project’s leader. 

When laser pulses are fired into the sky, a change in the refractive index of the air makes them shrink and become so intense that they ionise air molecules around them, causing them to heat up and race away at supersonic speeds, leaving a channel of low density, ionised air.

The channels created by LLR are therefore more electrically conductive than the surrounding air, and so form an easier path for the lightning to follow, changing its original trajectory. 

Eventually, the team behind the LLR project aims to use a laser to extend a 10-metre lightning rod’s influence by 500m, which could pave the way for laser-based lightning protection systems at airports, launchpads and tall buildings.

“Metal rods are used almost everywhere to protect from lightning, but the area they can protect is limited to a few metres or tens of metres,” said Houard. “The hope is to extend that protection to a few hundred metres if we have enough energy in the laser.”

But for future applications “it would be even better if we could trigger lightning,” Houard told AFP.

The research was published in the journal Nature Photonics.