Scientists have demonstrated that laser-induced filaments — formed in the sky by short and intense laser pulses — can guide lightning discharges over considerable distances.
The 124-m-high telecommunication tower of Säntis in Switzerland; also shown is the path of the laser recorded with its second harmonic at 515 nm. Image credit: Houard et al., doi: 10.1038/s41566-022-01139-z.
Lightning has fascinated and terrified humankind since time immemorial.
Based on satellite data, the total lightning flash rate worldwide — including cloud-to-ground and cloud lightning — is estimated to be between 40 and 120 flashes per second, causing considerable damage and casualties.
The most widely used external protection against direct lightning strikes is still the lightning rod, also known as Franklin rod or lightning conductor.
The lightning rod, whose invention in the 18th century is attributed to Benjamin Franklin, consists of a pointed conducting mast connected to the ground.
It protects buildings and their immediate surroundings by providing a preferential strike point for the lightning and guiding its electric current safely to the ground.
A method to initiate lightning discharges with a small rocket trailing a long, grounded conducting wire was demonstrated in 1965.
In contrast to the classical lightning rod, which is intended to be struck by lightning that approaches the protected structure, the rocket-and-wire technique is intended to trigger lightning artificially.
However, it requires expendable rockets and wires, the falling debris of which presents a danger.
The idea of using a laser to trigger lightning was first suggested by Leonard Ball in 1974.
A first attempt to trigger and guide natural lightning with lasers was made in 1999 using a combination of three small lasers to form a 2-m- (6.6-foot) long plasma spark.
In the new experiments, Dr. Aurélien Houard from the Laboratoire d’Optique Appliquée-ENSTA Paris and colleagues used a laser the size of a large car that fires up to a thousand pulses per second.
They installed the laser in the vicinity of a 124-m- (407-foot) tall telecommunications tower, which is struck by lightning around 100 times a year, located on top of the Säntis mountain in north-eastern Switzerland.
Over more than 6 hours of operation during thunderstorm activity, the laser diverted the course of 4 upward lightning discharges.
The observations were corroborated using high-frequency electromagnetic waves generated by the lightning to locate the strikes.
Increased detection of X-ray bursts at the time of the strikes also confirmed successful guiding.
One of the strikes was directly recorded by high-speed cameras and shown to follow the laser path for over 50 m (164 feet).
“Although this research field has been very active for more than 20 years, this is the first field-result that experimentally demonstrates lightning guided by lasers,” the authors said.
“This work paves the way for new atmospheric applications of ultrashort lasers and represents an important step forward in the development of a laser based lightning protection for airports, launchpads or large infrastructures.”
The results were published in the journal Nature Photonics.
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A. Houard et al. Laser-guided lightning. Nat. Photon, published online January 16, 2023; doi: 10.1038/s41566-022-01139-z
