Lasers can cool stuff, not just fry them
Washington: In a breakthrough, scientists have for the first time used a laser to refrigerate water and other liquids under real-world conditions.
University of Washington researchers used an infrared laser to cool water by about two degrees Celsius, becoming the first to solve a decades-old puzzle.
“Typically, when you go to the movies and see Star Wars laser blasters, they heat things up. This is the first example of a laser beam that will refrigerate liquids like water under everyday conditions,” said senior author Peter Pauzauskie, UW assistant professor of materials science and engineering.
The discovery could help industrial users “point cool” tiny areas with a focused point of light. Microprocessors, for instance, might someday use a laser beam to cool specific components in computer chips to prevent overheating and enable more efficient information processing. Scientists could also use a laser beam to precisely cool a portion of a cell as it divides or repairs itself, essentially slowing these rapid processes down and giving researchers the opportunity to see how they work.
Researchers chose infrared light for its cooling laser with biological applications in mind, as visible light could give cells a damaging “sunburn.” They demonstrated that the laser could refrigerate saline solution and cell culture media that are commonly used in genetic and molecular research.
To achieve the breakthrough, the UW team used a material commonly found in commercial lasers but essentially ran the laser phenomenon in reverse. They illuminated a single microscopic crystal suspended in water with infrared laser light to excite a unique kind of glow that has slightly more energy than that amount of light absorbed. This higher-energy glow carries heat away from both the crystal and the water surrounding it.
The laser refrigeration process was first demonstrated in vacuum conditions at Los Alamos National Laboratory in 1995, but it has taken nearly 20 years to demonstrate this process in liquids. The UW team demonstrated that a low-cost hydrothermal process can be used to manufacture a well-known laser crystal for laser refrigeration applications in a faster, inexpensive and scalable way. The team also designed an instrument that uses a laser trap—akin to a microscopic tractor beam - to “hold” a single nanocrystal surrounded by liquid in a chamber and illuminate it with the laser.
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To determine whether the liquid is cooling, the instrument also projects the particle’s “shadow” in a way that allows the researchers to observe minute changes in its motion. As the surrounding liquid cools, the trapped particle slows down, allowing the team to clearly observe the refrigerating effect. The study was published in the journal PNAS.
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