As they are cooled by the laser, the nanocrystals developed by the UW team emit a reddish-green “glow” that can be seen by the naked eye. Credit: Dennis Wise/University of Washington
Since the first laser was invented in 1960, they’ve always given off heat, but have never been able to cool liquids. University of Washington researchers are the first to solve a decades-old puzzle – figuring out how to make a laser refrigerate water and other liquids under real-world conditions.
They used an infrared laser to cool water by about 36F – a major breakthrough in the field.
It could help industrial users “point cool” tiny areas with a focused point of light. Eg Microprocessors 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. Or they could cool a single neuron in a network – essentially silencing without damaging it – to see how its neighbors bypass it and rewire themselves. “Using laser cooling, it may be possible to prepare slow-motion movies of life in action. And the advantage is that you don’t have to cool the entire cell, which could kill it or change its behavior.”
The UW team 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 commonly used in genetic and molecular research.
METHOD: They 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.
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 UW 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. 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.
So far, they have demonstrated the cooling effect with a single nanocrystal, as exciting multiple crystals would require more laser power. Future steps include looking for ways to improve its efficiency. One day the cooling technology itself might be used to enable higher-power lasers for manufacturing, telecommunications or defense applications, as higher-powered lasers tend to overheat and melt down.
http://www.washington.edu/news/2015/11/16/uw-team-refrigerates-liquids-with-a-laser-for-the-first-time/
Recent Comments