Lightning discharges between charged clouds and the Earth’s surface are responsible for significant damage and casualties. It is therefore important to develop better protection methods in addition to the traditional Franklin bar.
A European consortium comprising the University of Geneva (UNIGE), École Polytechnique (Paris), EPFL, the School of Engineering and Management HEIG-VD and TRUMPF Scientific Lasers (Munich) has developed a promising alternative: the Laser Lightning Rod or LLR. This laser lightning rod can deflect lightning over tens of meters, even in bad weather.
The LLR was used to direct lightning along its beam by producing channels of ionized air, which is electrically conductive, using strong laser pulses. By extending upwards from a conventional lightning rod, it can essentially increase both the height and the area of the area it shields.
As part of the LLR project, a new laser has been created with an average power of one kilowatt, a pulse energy of one joule and a pulse duration of one picosecond. The rod is 8 meters long, 1.5 meters wide and weighs more than 3 tons. It is made by TRUMPF Scientific Lasers.
The LLR’s terawatt laser was tested at the top of Säntis (2,502 meters above sea level), close to a Swisscom communications tower that is 124 meters high, and equipped with instruments from EPFL and HEIG-VD/HES-SO to observe lightning. The tower experiences lightning strikes about 100 times a year and is one of Europe’s lightning hotspots.
Scientists began to study the initiation of upward lightning discharges. They then deployed the experimental facilities for lightning observation in collaboration with the HEIG-VD/HES-SO. High-speed video cameras, X-ray sensors, electromagnetic field antennas, lightning current measurements on the tower, and an interferometric system to image the lightning discharge were among the instruments used.
Farhad Rachidi, in the School of Engineering, said: “This was a remarkable experimental achievement due to the multitude of measurement stations in a mountainous area with harsh weather conditions, all of which required time synchronization, monitoring and control capabilities.”
“These simultaneous observations allowed us to confirm the conduction of the lightning using the powerful laser.”
Aurélien Houard, a research scientist at the Laboratoire d’Optique Appliquée (LOA) and coordinator of the project, said: “Every time storm activity was predicted between June and September 2021, the laser was activated. The area had to be closed to air traffic in advance. The goal was to see if there was a difference with or without the laser.”
“We compared the data collected when the laser filament was produced above the tower and when the tower was naturally struck by lightning.”
It took scientists almost a year to analyze the collected data. They found that the LLR laser can effectively conduct lightning.
Jean-Pierre Wolf, UNIGE professor of physics and the study’s final author, said: “From the first lightning strike using the laser, we found that the discharge could follow the beam for almost 60 meters before reaching the tower, which means that the radius of the protection surface increased from 120 m to 180 m.”
- Houard, A., Walch, P., Produit, T. et al. Laser-guided lightning. Wet. Photon. (2023). DOI: 10.1038/s41566-022-01139-z