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    Scientists use laser to guide lightning bolt

    PARIS (AFP) – Scientists said on Monday they have used a laser beam to guide lightning for the first time, hoping the technique will help protect against deadly bolts – and one day maybe even trigger them.

    Lightning strikes between 40-120 times a second worldwide, killing more than 4,000 people and causing billions of dollars worth of damage every year.

    Yet the main protection against these bolts from above is still the humble lightning rod, which was first conceived by American polymath Benjamin Franklin in 1749.

    A team of scientists from six research institutions have been working for years to use the same idea but replace the simple metal pole with a far more sophisticated and precise laser.

    Now, in a study published in the journal Nature Photonics, they describe using a laser beam – shot from the top of a Swiss mountain – to guide a lightning bolt for more than 50 metres.

    “We wanted to give the first demonstration that the laser can have an influence on lightning – and it is simplest to guide it,” said physicist at the applied optics laboratory of the ENSTA Paris institute and the study’s lead author Aurelien Houard.

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

    Lightning is a discharge of static electricity that has built up in storm clouds, or between clouds and the ground.

    The laser beam creates plasma, in which charged ions and electrons heat the air. The air becomes “partially conductive, and therefore a path preferred by the lightning”, Houard said.

    When scientists previously tested this theory in New Mexico in 2004, their laser did not grab the lightning. That laser failed because it did not emit enough pulses per second for lightning, which brews in milliseconds, Houard said.

    He added that it was also difficult to “predict where the lightning was going to fall”.

    For the latest experiment, the scientists left little to chance. They lugged a car-sized laser – which can fire up to a thousand pulses of light a second – up the 2,500-metre peak of Santis mountain in northeastern Switzerland.

    The peak is home to a communications tower that is struck by lightning around 100 times year.

    After two years building the powerful laser, it took several weeks to move it in pieces via a cable car.

    Finally, a helicopter had to drop off the large containers that would house the telescope.

    The telescope focussed the laser beam to maximum intensity at a spot around 150 metres in the air – just above the top of the 124-metre tower.

    The beam has a diameter of 20 centimetres at the beginning, but narrows to just a few centimetres at the top.

    During a storm in the summer of 2021, the scientists were able to photograph their beam driving a lightning bolt for 50 around metres.

    Three other strikes were also guided, interferometric measurements showed.

    Most lightning builds up from precursors inside clouds, but some can come up from the ground if the electric field is strong enough.

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