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CHILL LASER

Now lasers can cool liquids down as well as heating things up

Laser Cooling
Dennis Wise/University of Washington
As they’re laser cooled, nanocrystals emit a reddish-green glow.
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Accompanied by traditional “pew pew” sound effects, we’re used to seeing lasers in sci-fi movies and TV shows blowing things up in a decidedly fiery way. But now scientists have worked out how to use real-life lasers to actually cool down liquids like water instead of heating them up.

Using an infrared laser, a University of Washington team has been able to cool liquids like water by as much as 36ºF  (2.2ºC). It sounds counter-intuitive because we’re used to thinking of lasers as highly focused, high-energy beams that are much more powerful than any other light source. Lasers blow missiles up, etch designs into wood, or cut incredibly precise holes in metal cases on the iPhone production line.

The new refrigeration trick involved shining a powerful infrared laser onto a single microcrystal suspended in water, exciting the crystal in a very particular way. The crystal glowed as a result. By a quirk of physics, glowing the crystal released just a bit more energy than it gained from being hit by the laser. The practical upshot of giving out more energy than you’re taking in is to cool down, and this is what happened to both the crystal and the water around it.

Dennis Wise/University of Washington
This instrument built by UW engineers (from left) Peter Pauzauskie, Xuezhe Zhou, Bennett Smith, Matthew Crane and Paden Roder (unpictured) used infrared laser light to refrigerate liquids for the first time.

Despite its futuristic-sounding name, laser refrigeration isn’t new, and research in the Los Alamos laboratory in the 1990s led to breakthroughs in laser cooling in a vacuum. But the setup wasn’t practical, and the new Washington research is the first time laser cooling has been seen in a “practical” environment.

But what’s it useful for? Right now the machinery required is complex, fiddly, and clumsily large and only works on one microcrystal. Don’t let this fool you: The first transistor was an impractical chunk of semiconductor the size of a fingernail. Scientists then advanced the technology so quickly that there are now countless billions of transistors sizzling away inside your super-skinny smartphone.

So while it’s currently a laboratory-scale task, laser cooling of liquids could one day allow ultra-precise cooling inside advanced computer chips, the cooling of high-power lasers themselves, because they have a tendency to overheat, or even enabling precise refrigeration of biological samples to boost experiments in fields like neuroscience.

You always knew lasers were cool. Now they’re even cooler.

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