Lasers Used to Cool Liquid for First Time

Researchers have created a specially designed crystal that glows with more energy than is contained in the light that illuminates it. It gradually uses up heat and cools its surroundings. Dennis Wise / University of Washington

Lasers are often used to heat things up, to melt and burn materials. But for the first time, researchers have used a laser and a small crystal to cool water, by a total of 36 degrees Fahrenheit (20 degrees Celsius).

Usually water "warms when illuminated," and "it was really an open question as to whether this could be done," said Peter Pauzauskie, a materials scientist and engineer at the University of Washington, in a statement.

The researchers accomplished the feat by reverse engineering a laser. First, they used a strong source of infrared light (or "laser"). Next, they designed a crystalline material called a laser crystal that, upon absorbing infrared radiation, was stimulated to emit light of a slightly higher energy content. They placed the small crystal in the liquid, and as it was illuminated with infrared light, it glowed red, emitting higher-energy light. This process uses up energy in the form of heat, gradually draining heat from the liquid and cooling it.

Often lasers work in the reverse way: Crystals emit a focused type of light when stimulated to do so, say by an electric field, creating a laser beam. But in this case, the crystal uses up heat as it emits light with a higher frequency, as it's stimulated by the infrared radiation, as noted in a study describing the finding published in the journal Proceedings of the National Academy of Sciences.

The effect is rather small and localized, but the scientists explain that this actually gives it a distinct upside. The advance could be used to cool small objects, like individual cells, for use in research or medical applications, or to prevent microprocessors from overheating.