'Dressed' laser aimed at clouds may be key to inducing rain, lightning

Apr 18, 2014
This is an illustration of the dressed filament that fuels the high-intensity laser to travel farther. Credit: Courtesy of University of Central Florida College of Optics and Photonics

The adage "Everyone complains about the weather but nobody does anything about it," may one day be obsolete if researchers at the University of Central Florida's College of Optics & Photonics and the University of Arizona further develop a new technique to aim a high-energy laser beam into clouds to make it rain or trigger lightning.

The solution? Surround the beam with a second beam to act as an energy reservoir, sustaining the central beam to greater distances than previously possible. The secondary "dress" beam refuels and helps prevent the dissipation of the high-intensity primary beam, which on its own would break down quickly. A report on the project, "Externally refueled optical filaments," was recently published in Nature Photonics.

Water condensation and lightning activity in clouds are linked to large amounts of static charged particles. Stimulating those particles with the right kind of laser holds the key to possibly one day summoning a shower when and where it is needed.

Lasers can already travel great distances but "when a becomes intense enough, it behaves differently than usual – it collapses inward on itself," said Matthew Mills, a graduate student in the Center for Research and Education in Optics and Lasers (CREOL). "The collapse becomes so intense that electrons in the air's oxygen and nitrogen are ripped off creating plasma – basically a soup of electrons."

At that point, the plasma immediately tries to spread the beam back out, causing a struggle between the spreading and collapsing of an ultra-short laser pulse. This struggle is called filamentation, and creates a filament or "light string" that only propagates for a while until the properties of air make the beam disperse.

"Because a filament creates excited electrons in its wake as it moves, it artificially seeds the conditions necessary for rain and lightning to occur," Mills said. Other researchers have caused "electrical events" in clouds, but not .

But how do you get close enough to direct the beam into the cloud without being blasted to smithereens by lightning?

"What would be nice is to have a sneaky way which allows us to produce an arbitrary long 'filament extension cable.' It turns out that if you wrap a large, low intensity, doughnut-like 'dress' around the filament and slowly move it inward, you can provide this arbitrary extension," Mills said.

"Since we have control over the length of a filament with our method, one could seed the conditions needed for a rainstorm from afar. Ultimately, you could artificially control the rain and lightning over a large expanse with such ideas."

So far, Mills and fellow graduate student Ali Miri have been able to extend the pulse from 10 inches to about 7 feet. And they're working to extend the filament even farther.

"This work could ultimately lead to ultra-long optically induced filaments or plasma channels that are otherwise impossible to establish under normal conditions," said professor Demetrios Christodoulides, who is working with the graduate students on the project.

"In principle such dressed filaments could propagate for more than 50 meters or so, thus enabling a number of applications. This family of optical filaments may one day be used to selectively guide microwave signals along very long plasma channels, perhaps for hundreds of meters."

Other possible uses of this technique could be used in long-distance sensors and spectrometers to identify chemical makeup. Development of the technology was supported by a $7.5 million grant from the Department of Defense.

Explore further: New laser technology could divert lightning strikes

More information: Nature Photonics 8, 297–301 (2014) DOI: 10.1038/nphoton.2014.47

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Dr_toad
Apr 18, 2014
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nkalanaga
not rated yet Apr 18, 2014
"In principle such dressed filaments could propagate for more than 50 meters or so"

50 meters isn't far enough from an artificially induced lightning bolt. The laser would still be vaporized... If all one wants is to induce lightning, a rocket trailing a wire is easier and cheaper, and it leaves no expensive equipment at ground zero.
alfie_null
not rated yet Apr 19, 2014
"In principle such dressed filaments could propagate for more than 50 meters or so"

50 meters isn't far enough from an artificially induced lightning bolt. The laser would still be vaporized... If all one wants is to induce lightning, a rocket trailing a wire is easier and cheaper, and it leaves no expensive equipment at ground zero.

The beam was described as an ultra-short pulse. Would the lightning be able to follow the beam to its source? If it could, wouldn't it be effective to wrap the laser equipment in shielding, a wire mesh, a Faraday cage? Surround it with attractive, pointy grounded electrodes that would divert the strike?

If I wanted to induce lightning strikes dozens or hundreds of times, the laser would be cheaper. Makes me wonder, what would be the result if you could effectively "discharge" storm clouds?
Z99
1 / 5 (1) Apr 19, 2014
alfie...seriously? yes of course a Faraday Cage would work - for about a microsecond - then the current flow would vaporize the superheated metal. You should learn something about lightning and electricity, like resistance increases with temperature, temperature increases with current flow, and metals melt. Lightning is a really fascinating subject. But first, suggest you get up to speed on H.S. physics.
Sean_W
not rated yet Apr 19, 2014
alfie...seriously? yes of course a Faraday Cage would work - for about a microsecond - then the current flow would vaporize the superheated metal. You should learn something about lightning and electricity, like resistance increases with temperature, temperature increases with current flow, and metals melt. Lightning is a really fascinating subject. But first, suggest you get up to speed on H.S. physics.


It's just an engineering issue. Lightning hits metal objects all the time without vaporizing them. You just need to provide a path which lower resistance than the path passing through your device which is also capable of handling the current. A metal dome which is well grounded with a small hole for the laser should work.
Sean_W
not rated yet Apr 19, 2014
"It turns out that if you wrap a large, low intensity, doughnut-like 'dress' beam around the filament and slowly move it inward, you can provide this arbitrary extension," Mills said.


That sounds like the most important part of this research boiled down into a throw away comment. Is it easy to create doughnut-like 'dress' beams and slowly move them inward?
nkalanaga
not rated yet Apr 19, 2014
alfie_null: I think the lightning would be able to follow the beam back, because it would actually follow the residual ionization. The Faraday shield probably wouldn't work, but enough lightning rods likely would. After all, they survive strikes everyday.