Lasers Eyed To Cool Satellite Cameras, Night-Vision Goggles

January 23rd, 2013 | by Charles Q. Choi

Instead of using lasers to heat targets, now researchers are shooting light beams that cool what they shine on.

Scientists want to see if novel refrigerators based on this research could reach temperatures just a few degrees above the coldest possible—absolute zero.
Normal refrigerators use motors to pump compressed gas through tubes lining them. As these gases expand, they remove heat from inside the appliance.

Laser refrigerators

The technique whereby lasers can be used to cool targets is called optical refrigeration. It works like this: lasers focused on an object can make it fluoresce, which causes it to lose energy as light and decrease in temperature. Optical refrigerators potentially have a number of advantages over conventional units. Since they require neither gas nor moving parts, they can be more compact, free from vibration and not prone to mechanical failure.

Although optical refrigeration of solids was first predicted in 1929, it was not seen experimentally until 1995 with glassy and crystalline materials doped with rare earth metals. In less than 20 years, research using these materials has advanced optical refrigeration enough to achieve cooling from room temperature to about -260 degrees Fahrenheit. Still, that is significantly warmer than the -321 degrees F at which liquid nitrogen boils.

Scientists wanted to accomplish optical refrigeration with semiconductors instead of rare-earth-metal-doped glasses and crystals. Semiconductors are the basis of modern electronics, and so researchers strove to directly integrate optical refrigerators into existing devices. Calculations also suggested that optical refrigerators that used semiconductors could achieve much lower temperatures. However, attempts to develop the units based on the semiconductor gallium arsenide failed. Although this semiconductor does fluoresce when hit by lasers, the emitted light does not escape from the material efficiently, so it heats up instead of cooling down.

Now, using the semiconductor cadmium sulfide, researchers have shown that lasers could trigger cooling, from about 62 degrees F to about -9 degrees F.

Read more: txchnologist.com: Lasers Eyed To Cool Satellite Cameras, Night-Vision Goggles.

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