Physicists have just set a new record by trapping a self-focused laser pulse in an air cage along a 45-meter-long university corridor.
Led by physicist Howard Milchburg of the University of Maryland (UMD), the new experiment breaks new ground in confining light in channels called air waveguides.
The results of this research have been accepted by Physical Review X and are available on the arXiv preprint server. This result may provide new hints for realizing long-distance communication using lasers and advanced weapons technology using lasers.
“Our results show that if we had a longer waveguide, we could have tuned the laser,” says UMD physicist Andrew Tartaro.
“But we did the right thing with the passage guidance we have now.”
Lasers can be used in a variety of applications, but an ordered, coherent beam of light must be somehow collected and focused. If left unattended, the laser will scatter, reducing power and efficiency.
Waveguide, as the name suggests, is a technology that guides electromagnetic waves to a specific path and prevents scattering.
One example is fiber optics. It consists of a glass tube that allows electromagnetic waves to pass through. The outer cladding of the tube has a lower refractive index than the center of the tube, so light that would otherwise be scattered is deflected inside the tube, keeping the beam along its length.
In 2014, Milchberg and colleagues successfully demonstrated what they call an air waveguide. Instead of using a physical structure like a tube, they used laser pulses to focus the laser light.
As a result, they found that a pulsed laser generates a plasma that heats the air on its path, leaving a path of less dense air. As the less dense air expands, it creates tiny thunderous sounds that follow the laser to form what is called a filament.
Less dense air has a lower refractive index than the surrounding air, like the cladding of a fiber optic tube. So, by launching these filaments in a specific arrangement to “cradle” the laser light, it is possible to form a waveguide out of the air.
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