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NTU team uses lasers to cool things down

The laser cooling discovery by Prof Xiong and his NTU team was featured in prestigious scientific journal Nature two weeks ago.
The Straits Times - February 5, 2013
By: Grace Chua
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NTU team uses lasers to cool things down The laser cooling discovery by Prof Xiong and his NTU team was featured in prestigious scientific journal Nature two weeks ago. -- PHOTO: NANYANG TECHNOLOGICAL UNIVERSITY

BULKY in-built computer fans and huge tanks of liquid helium used as industrial cryogenic coolants could one day be replaced by lasers as compact cooling agents.

Assistant Professor Xiong Qihua, 39, and his team from Nanyang Technological University's (NTU) physics and electrical and electronic engineering schools have found that some lasers can interact with a semiconductor called cadmium sulfide to cool it down.

This is the first time researchers anywhere have performed this work on a semiconductor material, which in turn means computer chips could one day be cooled by lasers instead.

The NTU team's work was published in and featured on the cover of prestigious scientific journal Nature less than two weeks ago.

Laser cooling works because the semiconductor material absorbs the laser's light energy and reflects considerably more light and energy (a combination known as luminescence) than it absorbs from the laser.

This unequal exchange results in the semiconductor shedding energy, because its molecules vibrate less, thus losing heat in the process.

In the lab, it takes half an hour to cool a semiconductor fragment smaller than a fingernail by 40 deg C, from 20 deg C to minus 20 deg C.

At the moment, the process works only on cadmium sulfide that Prof Xiong's team grew in laboratory conditions.

But the next steps for the team are to find other materials the process works on; cool them to even lower temperatures, on a par with liquid-helium cooling; and cool larger sheets of semiconductor material.

"Here, we are using a very unique process," Prof Xiong said.

"I doubt it will be replacing air conditioning, which is already very efficient.

"Its advantage is not cooling efficiency but compactness," he added, as well as the fact that it could potentially do away with bulky liquid refrigerants.

caiwj@sph.com.sg

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