Researchers cool a liquid for the first time by laser

Novel laser cooling could create cold spots in electronics and cell research

Upon irradiation with an infrared laser, the nanocrystal gives off green light and removes heat from the surrounding liquid. © Dennis Wise / University of Washington
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Cooled by light: For the first time, US researchers have succeeded in cooling down a saline solution by laser. Instead of heating the drop, the laser lowered its temperature by 15 degrees. This was made possible by a special crystal, which starts to shine through the laser light and thus withdraws heat from the surrounding liquid. Once optimized, this laser cooling system could be used to cool even the smallest computer components or even individual cell processes, according to the scientists.

It is highly pure, radiates thousands of miles without fanning and can even cut steel: lasers emit light in its most concentrated form and this is correspondingly high in energy. That's why lasers are ideal for cutting, drilling and welding - even as a weapon you could use them. The fact that one can also cool with a laser, therefore seems paradoxical at first. "Typically, when you see a laser blaster in a movie, for example, they heat things up, " says Peter Pauzauskie of the University of Washington.

But for gases and atomic clouds, for example in atomic clocks, laser cooling has long been common. Certain crystals can also be cooled by this method. For liquids, however, it seemed impossible. "It was an open question if you could do that because water normally heats up when you use a laser, " says Pauzauskie.

The YLF crystal under the microscope during laser bombardment Pauzauskie et al. / PNAS

Nanocrystal as heat dissipator

In their experiment, however, the researchers used a trick: They first generated a microscopic crystal of yttrium-lithium fluoride (YLF). These crystals are known to be cooled in vacuo by infrared lasers. They place this crystal in a saline solution, as it corresponds, for example, to the liquid in cells and tissues.

When the crystal was irradiated with an infrared laser, it released excess energy in the form of a blue-green glow. This process not only removed heat from the crystal itself, but also from the surrounding saline solution. This cooled by up to 15 degrees Celsius. "This is the first example of a laser that can cool liquids like water under all conditions, " says Pauzauskie. display

Application in electronics and cell biology

The whole thing still only works with a single nanocrystal and a correspondingly small amount of liquid. In addition, the laser needs a lot of energy for this. But the researchers are sure that this process can be optimized. Then this laser cooling could prove useful in several ways.

"Potential applications range from precise temperature control of microchips, photonic or microfluidic circuits to triggering and exploring basic metabolic processes at the cellular level, " said the researchers. Thus, with such a cooling laser, tiny cooling points can be generated, by means of which, for example, a single cell or even only cell components can be cooled down. As this causes the cell processes to run in quasi-slow motion, this allows the targeted observation of these processes.

"With laser cooling, it could be possible to make slow motion films of life into action, " says Pauzauskie. "And the advantage of this is that you do not have to refrigerate the entire cell, which could kill them, or change their behavior." (Proceedings of the National Academy of Sciences (PNAS), 2015; doi: 10.1073 / pnas.1510418112)

(University of Washington, 18.11.2015 - NPO)