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ScienceSwiss researchers manage to guide lightning with a laser
During an experiment carried out at Mount Säntis, in Appenzell, in particular by the University of Geneva, a laser beam could be used as a lightning rod. A scientific first.
In these photographs taken at the Schwägalp pass (left) and Kronberg (right), you can see the powerful laser beam attracting lightning like a lightning rod.
AFP/ENSTA Paris – Polytechnic Institute of Paris
Guide lightning, and why not trigger it one day: this is the bet of scientists who bring the first experimental demonstration with a laser at the top of a Swiss mountain, as reported in a study published Monday.
“We wanted to make a first demonstration that the laser can have an influence on lightning, and the simplest thing is to guide it”, explains Aurélien Houard, from the Applied Optics Laboratory at ENSTA-École Polytechnique in the region. Parisian.
It is the culmination of a twenty-year collaboration with physicist Jean-Pierre Wolf, from the Applied Physics Group at the University of Geneva, and involving six institutes.
Lightning kills more than 4,000 people a year worldwide
Lightning strikes, which occur 40 to 120 times per second around the globe, cause more than 4,000 deaths each year and economic damage amounting to billions of dollars, recalls the study published in “Nature Photonics”.
Since the invention of the lightning rod attributed to Benjamin Franklin in the 18the century, science has only made progress in protecting itself from it by building ever higher masts to guide it.
Aurélien Houard and Jean-Pierre Wolf’s team used a laser as a lightning rod. Its beam creates a plasma, air charged with ions and electrons, which is also heated by this process. The air crossed by the beam “then becomes partially conductive, and thus a preferential path for lightning”, a bit like a cable, explains Aurélien Houard.
First failed attempt in 2004
Scientists had unsuccessfully tested this theory during a campaign in New Mexico in 2004. The fault was a poorly adapted laser, and terrain where it is difficult to predict where the lightning will fall.
The solution? They found it at the top of Mount Säntis, 2500 m above sea level in the Prealps of northeastern Switzerland. The icing on the cake, the place is equipped with a 124 m high telecommunications tower, struck with the quasi-regularity of a clock at the rate of 100 lightning strikes per year.
Two years to build a super-powerful laser
After two years of building a very powerful laser, made by the German Trumpf, and several weeks of mounting it in pieces by cable car, the largest helicopter in Switzerland has deposited containers there to house a telescope. The telescope is used to focus the laser beam to obtain the strongest intensity at 150 meters high. The green beam of the laser goes from a diameter of 20 cm at the start to a few centimeters.
In the summer of 2021, the scientists tuned their laser to create a plasma above the tip of the tower. And managed to photograph the guidance of a flash of lightning by the laser for about 50 meters. Three other guidances were corroborated by interferometry measurements.
Better protect airports or rocket launch pads
Lightning develops with precursors (similar to branches) that start from the clouds, and from the ground when the electric field is strong enough. It is through the junction of these precursors that “the current and the power of a lightning bolt really appear, once the ground is connected with the cloud”, explains Aurélien Houard.
The laser guides one of these precursors. Thanks to this, “he will go much faster than the others and straighter. He will then be the first to connect with the cloud before lighting up. In the end, this precursor becomes the lightning bolt.”
Once the demonstration has been made that a flash of lightning can be guided, it remains to be confirmed by other experiments. And then to try to trigger lightning, to better protect strategic installations, such as airports or rocket launch pads. It would suffice in theory to launch precursors, and in practice to have a fairly high conductivity in the plasma. What researchers do not think they have yet mastered.
(AFP)