UW Researchers refrigerate liquids with a laser for the first time

The UW team has only demonstrated the cooling effect with a single nanocrystal.

AB Wire

Since the first laser was invented in 1960, they’ve almost always given off heat — either as a useful tool, a by-product or a fictional way to vanquish intergalactic enemies.

But those concentrated beams of light 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.

In a study to be published the week of Nov. 16 in the Proceedings of the National Academy of Sciences, the team used an infrared laser to cool water by about 36 degrees Fahrenheit — a major breakthrough in the field.

“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.

“It was really an open question as to whether this could be done because normally water warms when illuminated.”

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 real challenge of the project 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,” said lead author Paden Roder, who recently received his doctorate from the UW in materials science and engineering and now works at Intel Corp.

So far, the UW team has only 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.

“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,” Pauzauskie said.

“We are interested in the ideas other scientists or businesses might have for how this might impact their basic research or bottom line.”