The adage 麻豆精品 S淓veryone complains about the weather but nobody does anything about it, 麻豆精品 S� may one day be obsolete if researchers at the University of Central Florida 麻豆精品 S檚 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 麻豆精品 S渄ress 麻豆精品 S� 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, 麻豆精品 S淓xternally refueled optical filaments, 麻豆精品 S� 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 麻豆精品 S渨hen a laser beam becomes intense enough, it behaves differently than usual 麻豆精品 S� it collapses inward on itself, 麻豆精品 S� said Matthew Mills, a graduate student in the Center for Research and Education in Optics and Lasers (CREOL). 麻豆精品 S淭he collapse becomes so intense that electrons in the air 麻豆精品 S檚 oxygen and nitrogen are ripped off creating plasma 麻豆精品 S� basically a soup of electrons. 麻豆精品 S�
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 麻豆精品 S渓ight string 麻豆精品 S� that only propagates for a while until the properties of air make the beam disperse.
麻豆精品 S淏ecause a filament creates excited electrons in its wake as it moves, it artificially聽seeds聽the conditions necessary for rain聽and lightning to occur, 麻豆精品 S� Mills said. Other researchers have caused 麻豆精品 S渆lectrical events 麻豆精品 S� in clouds, but not lightning strikes.
But how do you get close enough to direct the beam into the cloud without being blasted to smithereens by lightning?
麻豆精品 S淲hat would be nice is to have a sneaky way which allows us to produce an arbitrary long 麻豆精品 S榝ilament extension cable. 麻豆精品 S� It turns out that if you wrap a large, low intensity, doughnut-like 麻豆精品 S榙ress 麻豆精品 S� beam around the filament and slowly move it inward, you can provide this arbitrary extension, 麻豆精品 S� Mills said. 麻豆精品 S淪ince we have control over the length of a filament with our method, one could聽seed the conditions needed for a rainstorm from afar. Ultimately, you could artificially聽control the rain and lightning over a large expanse with such ideas. 麻豆精品 S�
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 麻豆精品 S檙e working to extend the filament even farther.
麻豆精品 S淭his work could ultimately lead to ultra-long optically induced filaments or plasma channels that are otherwise impossible to establish under normal conditions, 麻豆精品 S� said professor Demetrios Christodoulides, who is working with the graduate students on the project.
麻豆精品 S淚n 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. 麻豆精品 S�
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.