For the first time, a team from the University of Washington has cooled down a liquid using a laser. They were able to cool down water by 20°C (36°F) using an infrared laser – a significant breakthrough in the decades-long quest of achieving laser refrigeration in real-life conditions.
"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 in a statement. "It was really an open question as to whether this could be done because normally water warms when illuminated."
The researchers shined an infrared laser onto a special microscopic crystal; the excited crystal then emits visible light (in a reddish-green colour) which is slightly more energetic than the light received from the laser. The extra energy needed for this shift from infrared to visible needs to come from somewhere, so the nanocrystal steals it from the liquid that surrounds it, effectively cooling it.
Laser refrigeration was first demonstrated in a vacuum in 1995, but this is the first time it has been shown to work on liquids. The effect was only demonstrated on a single nanocrystal; scaling the effect on multiple crystals would require more powerful lasers. "The laser refrigeration process is currently quite energy intensive," Pauzauskie said, "and future steps include looking for ways to improve its efficiency."
The success and applicability of this development has far-reaching consequences in science and technology, beyond threatening a city with terrible ice puns. For example, the ability to reduce temperature in a stable and controlled way can help scientists slow down biological and chemical processes.
"There’s a lot of interest in how cells divide and how molecules and enzymes function, and it’s never been possible before to refrigerate them to study their properties," added Pauzauskie. "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 team hopes that this research, to be published this week by the Proceeding of the National Academy of Sciences, will pique the interest of other scientists.
"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," Paden Roder, lead author of the study, commented. "We are interested in the ideas other scientists or businesses might have for how this might impact their basic research or bottom line."