Scientists have developed a new technology that can send high-intensity laser beams through the atmosphere much farther than was possible before, and it could one day be used to guide lightning away from buildings.
The breakthrough, by scientists at the University of Arizona and the University of Central Florida, was made possible by embedding the primary, high-intensity laser beam inside a second beam of lower intensity.
As the primary beam travels through the air, the second beam - called dress beam - refuels it with energy and sustains the primary beam over much greater distances than were previously achievable.
"Think of two airplanes flying together, a small fighter jet accompanied by a large tanker," said Maik Scheller, an assistant research professor in the UA College of Optical Sciences.
"Just like the large plane refuels the fighter jet in flight and greatly extends its range, our primary, high-intensity laser pulse is accompanied by a second laser pulse - the "dress" beam - which provides a constant energy supply to compensate for the energy loss of the primary laser beam as it travels farther from its source," Scheller said.
Unlike conventional lasers, the laser bursts used in this research pack extremely high energy into very short timespans on the order of a femtosecond; a billionth of a millionth of a second, researchers said.
"Usually, if you shoot a laser into the air, it is limited by linear diffraction. But if the energy is high enough and condensed into a few femtoseconds, creating a burst of light of extremely high intensity, it propagates through the air in a different way due to self-focusing," Scheller said.
"The problem is that as it also ionises the air and creates a plasma, so the laser loses energy," Scheller said.
The filament doesn't go very far because of the energy loss that ultimately causes the laser to dissipate. The dress beam used in Scheller's research overcomes this limitation.
Similar to the principle of noise-cancelling headphones, the energy loss of the primary laser beam and the energy supply from the dress laser beam cancel each other out.
In the lab, the researchers were able to extend the range of filament lasers tenfold - from about 10 inches to 7 feet.
Simulations performed by Matthew Mills at the University of Central Florida have shown that by scaling the new laser technology to atmospheric proportions, the range of the laser filaments could reach 50 metres or more.
As the filaments travel through the air, they leave a channel of plasma in their wake - ionised molecules stripped of their electrons.
Such plasma channels could be used as a path of least resistance to attract and channel lightning bolts. Ultimately, this technology could be used to control lightning bolts during a thunderstorm and steer them away from buildings, researchers said.