Physicists fire a dangerously powerful laser down their corridor in the middle of the night

What happens when physicists decide that their lab is too small? Some start to fire powerful lasers down the corridor in the middle of the night.

This wasn’t just a bunch of undergraduates playing laser skirmish when they got bored.

The US researchers had been investigating “optical guiding”: a method of directing light through air, which could be used for long-range laser communication.

They’d shown that this works over distances smaller than a metre, but they couldn’t expand their reach because their lab was too small, and the extremely powerful laser they used couldn’t be easily moved.

Their solution? Make a hole in the wall and fire the laser into the 50-metre long hallway.

“There were major challenges: the huge scale-up to 50 metres forced us to reconsider the fundamental physics of air waveguide generation, plus wanting to send a high-power laser down a 50-meter-long public hallway naturally triggers major safety issues,” says Professor Howard Milchberg, a physicist at the University of Maryland, US.

Three people in sunglasses standing in corridor working on laser
Left to right: Eric Rosenthal, a physicist at the U.S. Naval Research Laboratory; Anthony Valenzuela, a physicist at the U.S. Army Research Lab; and Andrew Goffin, a UMD electrical and computer engineering graduate student, align optics at a porthole in the wall in order to send the laser beam from the lab down the hallway. Credit: Intense Laser-Matter Interactions Lab, UMD

“Fortunately, we got excellent cooperation from both the Physics (Department) and from the Maryland environmental safety office!”

This is important, because the laser is powerful enough to burn paper and skin.

The researchers did their work at night, so they could block off the corridor with minimal inconvenience to their co-inhabitants.

“It was a really unique experience,” says Andrew Goffin, an electrical and computer engineering graduate student at the University of Maryland.

“There’s a lot of work that goes into shooting lasers outside the lab that you don’t have to deal with when you’re in the lab – like putting up curtains for eye safety. It was definitely tiring.”

Read also: Powerful lasers can control lightning strikes

After several nights of testing, the researchers found their waveguide technique could conserve roughly 20% of the light that would normally be dissipated through the air. With more testing, they believe they can make the guide more efficient.

“If we had a longer hallway, our results show that we could have adjusted the laser for a longer waveguide,” says physics graduate student Andrew Tartaro.

Two laser points with picture on the right more concentrated
Distributions of the laser light collected after the hallway journey without a waveguide (left) and with a waveguide (right). Credit: Intense Laser-Matter Interactions Lab, UMD

“Based on new lasers we are soon to get, we have the recipe to extend our guides to one kilometer and beyond,” says Milchberg.

A paper describing their experiment has been accepted by Physical Review X.

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