Lasers used as lightning rods in new study
by Christopher McFadden  /  Jan 16, 2023

“According to a report published in Nature Photonics, an intense laser pointed at the sky can act as a virtual lightning rod and alter the route of lightning strikes. The research could improve lightning protection strategies for vital infrastructure like power plants, airports, and launch pads. A “Franklin rod” an electrically conducting metal mast that intercepts lightning discharges and directs them safely to the ground, is now the most popular lightning protection device. These rods, also known as “rod and reel” lightning rods, work by attracting and conducting electrical charges from a thunderstorm to the ground.

They consist of a pointed metal rod placed on top of a building or other structure and a wire that runs from the rod down to a grounding system. When a thunderstorm approaches, the electrical charges in the storm clouds are attracted to the pointed rod, which acts as a conductor. The charges are then safely conducted down the wire to the ground, reducing the risk of damage from a lightning strike. Interestingly, if the research is anything to go by, an alternative might be a laser beam pointed at the sky. Such a virtual rod would also be highly mobile.

The use of lasers as lightning rods is a theoretical concept that is still being researched. The idea is that a high-powered laser beam could be directed into the atmosphere in order to ionize a path for lightning to follow, in effect “guiding” the lightning strike to a specific location where it can be safely grounded. This concept is based on the principles of laser-induced breakdown, where a high-intensity laser beam creates a plasma channel in a gas, which can then conduct electricity. That is, until now: Intense laser pulses have been used to guide lightning strikes in laboratory settings before; however, there has never been a field finding that experimentally shows lightning guidance by lasers.

On the Säntis Mountain in northeastern Switzerland, Aurélien Houard and associates conducted experiments in the summer of 2021 to determine whether a laser might direct a lightning strike. A massive car-sized laser that can fire up to 1,000 pulses per second was placed next to a communications tower that experiences lightning strikes about 100 times yearly. The scientists noted that during more than 6 hours of operation during thunderstorm activity, the laser changed the path of 4 upward lightning discharges.

High-frequency electromagnetic waves produced by lightning strikes were used to pinpoint the strikes to confirm their observations. Greater X-ray burst detection during the time of the impacts also confirmed successful lightning directing. High-speed cameras directly captured one of the strikes, which was later proved to have followed the laser path for more than 164 feet (50 meters). According to the scientists, the findings contribute to our present understanding of laser physics in the atmosphere and could be used to create fresh approaches to lightning protection.

“This 3-D reconstruction shows the moment the lightning bolt hit a metal rod atop a tower, its path guided by a powerful laser.”

You can read the study for yourself in the journal Nature Photonics.

Study abstract: “Lightning discharges between charged clouds and the Earth’s surface are responsible for considerable damages and casualties. It is, therefore important to develop better protection methods in addition to the traditional Franklin rod. Here we present the first demonstration that laser-induced filaments—formed in the sky by short and intense laser pulses—can guide lightning discharges over considerable distances.

We believe that this experimental breakthrough will lead to progress in lightning protection and lightning physics. An experimental campaign was conducted on the Säntis mountain in northeastern Switzerland during the summer of 2021 with a high-repetition-rate terawatt laser. The guiding of an upward negative lightning leader over a distance of 50 m was recorded by two separate high-speed cameras.

“a,b, Snapshot recorded by the two high-speed cameras located at Schwaegalp (a) and Kronberg (b). The trajectory of the laser path taken subsequently in clear sky through second harmonic generation is also overlaid.”

The guiding of negative lightning leaders by laser filaments was corroborated in three other instances by very high-frequency interferometric measurements, and the number of X-ray bursts detected during guided lightning events greatly increased. 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. 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.”

A powerful laser can redirect lightning strikes
by Maria Temming  /  January 16, 2023

“In a mountaintop experiment, a powerful laser bent lightning toward a lightning rod, researchers report online January 16 in Nature Photonics. Scientists have used lasers to wrangle electricity in the lab before, but this is the first demonstration that the technique works in real-world storms and could someday lead to better protection against lightning.

Today’s most common anti-lightning tech is the classic lightning rod, a meters-long metal pole rooted to the ground. The metal’s conductivity lures in lightning that might otherwise strike nearby buildings or people, feeding that electricity safely into the earth. But the area shielded by a lightning rod is limited by the rod’s height. “If you want to protect some large infrastructure, like an airport or a launching pad for rockets or a wind farm … then you would need, for good protection, a lightning rod of kilometer size, or hundreds of meters,” says Aurélien Houard, a physicist at Institut Polytechnique de Paris in Palaiseau, France.

Such a tall metal pole would be impractical. But a laser could reach that far, intercepting distant lightning bolts and ushering them down to ground-based metal rods. Houard and his colleagues tested this idea atop the Säntis mountain in northeastern Switzerland. They set up a high-power laser near a telecommunications tower tipped with a lightning rod that is struck by lightning around 100 times every year. The laser was beamed at the sky for about six hours total during thunderstorms from July to September 2021.

The laser blasted short, intense bursts of infrared light at the clouds about 1,000 times per second. This train of light pulses ripped electrons off air molecules and knocked some air molecules out of its way, carving out a channel of low-density, charged plasma. Sort of like clearing a path through the woods and laying down pavement, this combination of effects made it easier for electric current to flow along this route (SN: 3/5/14). That created a path of least resistance for lightning to follow through the sky. Houard’s team tuned their laser so that it formed this electrically conductive pathway just above the tip of the tower. This allowed the tower’s lightning rod to intercept a bolt snagged by the laser before it zipped all the way down to the laser equipment.

The tower was hit by lightning four times while the laser was on. One of those strikes happened in a fairly clear sky, allowing two high-speed cameras to capture the moment. Those images showed lightning zigzagging down from the clouds and following the laser light for some 50 meters toward the tower’s lightning rod. To track the paths of the three bolts that they could not see, the researchers looked at radio waves shed by the lightning. Those radio waves showed that the three strikes followed the path of the laser much more closely than other strikes that happened when the laser was off. This hinted that the laser guided these three strikes to the lightning rod, as well.

“Fairly clear skies allowed a high-speed camera to capture the moment that a laser bent the path of a lightning bolt between the sky and a lightning rod atop a tower. The lightning followed the route of the laser light for some 50 meters.”

“It’s a real achievement,” says Howard Milchberg, a physicist at the University of Maryland in College Park not involved in the work. “People have been trying to do this for many years.” Scientists’ main goal in bending lightning to their will is to increase safety, he says. But “if this thing ever became really, really efficient, and the probability of guiding a discharge was increased way beyond what it is now, it could potentially even be useful for charging things up.”

Atmospheric and space scientist Robert Holzworth is more cautious about imagining the applications. “They only showed 50 meters of [guiding] length, and most lightning channels are kilometers long,” says Holzworth, of the University of Washington in Seattle. So scaling the laser system up to have a useful reach may take a lot of work. Using a higher-frequency, higher-energy laser could extend its reach, Houard says. “This is a first step toward a kilometric-range lightning rod.”



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