Articles
Credit: Dennis Wise / University of Washington
Researchers have used a laser for the first time to chill water, opening up the possibility of higher-powered lasers and the ability to chill materials with pinpoint accuracy.
The study by scientists at the University of Washington, used an infrared laser to cool water by about 36 degrees Fahrenheit by illuminating a single microscopic 'nanocrystal' suspended in water, and essentially “running the laser in reverse”.
The crystal, which the University of Washington said is a material commonly found in commercial lasers, emits a glow that carries heat away from both the crystal and the water surrounding it.
The process was first demonstrated in vacuum conditions at Los Alamos National Laboratory in 1995, but it has taken nearly 20 years to demonstrate in liquids.
Paden Roder, lead researcher on the project, said: "The real challenge was building an instrument and devising a method capable of determining the temperature of these nanocrystals using signatures of the same light that was used to trap them,"
The team designed and used a laser trap to 'hold' a single nanocrystal surrounded by liquid in a chamber and illuminate it with the laser. 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. They also designed the crystal to change from a blueish-green to a reddish-green color as it cools, like a built-in color thermometer.
The research also 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.
Possible applications for the cooling technology could be to enable higher-power lasers for manufacturing, telecommunications or defence applications, as higher-powered lasers tend to overheat and melt down. The research could help industrial users "point cool" tiny areas with a focused point of light, opening up the possibility of cooling computer chips and other components in computers.
Peter Pauzauskie, assistant professor of materials science and engineering, at the University of Washington, said: "Few people have thought about how they could use this technology to solve problems because using lasers to refrigerate liquids hasn't been possible before. We are interested in the ideas other scientists or businesses might have for how this might impact their basic research or bottom line."
So far, the researchers have demonstrated the cooling effect with a single nanocrystal, as exciting multiple crystals would require more laser power. The laser refrigeration process is currently quite energy intensive, Pauzauskie said, and future steps include looking for ways to improve its efficiency.