Optical Refrigeration: Researchers Achieve Milestone in Laser Cooling

January 19, 2010
Researchers Achieve Milestone in Laser Cooling
Students Denis Seletskiy and Seth Melgaard in the lab. The pair, along with Professor Mansoo Sheik-Bahae and other researchers made a promising breakthrough in optical refrigeration with a novel alternative to bulky mechanical cryo-coolers.

(PhysOrg.com) -- Researchers at the University of New Mexico have established a new low in temperature cooling through laser cooling of solids to cryogenic temperatures. Under an AFOSR, MURI grant, a team led by UNM Professor, Mansoor Sheik-Bahae, created the first-ever all-solid-state cryocooler (temperatures that can only be obtained by liquefying gases and mechanical refrigerators) that can be used for a variety of applications ranging from cooling infrared sensors to superconducting electronics.

This work was just published in the January (online) issue of . To view the paper visit: of solids to cryogenic temperatures.

Graduate students Denis Seletskiy and Seth Melgaard designed and performed the experiments at UNM's Department of Physics and Astronomy in collaboration with researchers from Los Alamos National Lab and the University of Pisa, Italy.

The consortium research project grew out of a collaboration with Los Alamos National Labs more than seven years ago. Laser cooling of solids, also known as "optical refrigeration", is the process of lowering the temperature of a solid by shining laser light on it. The heat is carried away from the material via fluorescence that follows the laser absorption.

Early experiments at Los Alamos back in 1995 led to a cooling of about 1 degree cooling. Subsequent improvements led to an absolute temperature of 208 (K) or -65 degrees Celsius starting from room temperature. Further improvements, including extremely high-purity materials, together with gaining better insight into the physics of luminescent crystals have enabled the researchers at UNM to reach a new milestone by cooling to temperatures below what is achievable by standard thermoelectric (also known as Peltier) coolers.

“We obtained cooling down to 155 Kelvin (equivalent to -118 C or -180 F) from room temperature using optical refrigeration in a crystal containing Ytterbium ions. Ytterbium is an element from a group in the period table known as the rare-earths that are extremely efficient in their fluorescence, an essential requirement for optical refrigeration” said Sheik-Bahae. “We expect that material research may soon lead to temperatures dipping below 77K, the boiling point of liquid nitrogen, and in the future, maybe as low as 10K will be possible.”

To achieve their results, the scientists enhanced cooling efficiency by exploiting resonances in the absorption spectrum, growing pure crystals, delicate thermal load management and by trapping laser light in an optical cavity.

“We tune high power lasers to excite sharp resonances of Ytterbium ions sitting in a fluoride crystalline host,” explained Seletskiy. “We trap by careful alignment of the optical cavity mirrors inside of a high vacuum chamber. A specially designed and coated sample chamber allows us to minimize parasitic heat load from the environment.

“We infer crystal temperature using a technique we developed that allows to measure temperature without making a contact with the sample, further avoiding unnecessary parasitic heat load on the sample. Combination of all of these ideas and tricks has allowed us to reach 155K, breaking ‘Peltier barrier.’

“We’ve set the bar high or low in this case,” said Sheik-Bahae. “We feel 100K is within reach and also 77K, the melting point of liquid nitrogen. In the end, it is primarily materials science that is allowing this breakthrough. Reaching those temperatures is achievable using high purity crystals.”

Further advances in this technology may lead to applications in cooling superconducting electronics, infrared and gamma-ray sensors. Many other novel applications where miniaturized cryocoolers are needed will also benefit from this technology. Previously, solid-state coolers, based on standard thermoelectric (Peltier) devices, have only been able to reach temperatures as low as 170K, however with minimal efficiency.

Sheik-Bahae and his team will continue collaborations with Professor Mauro Tonelli and his researchers at the University of Pisa in Italy as well as with Richard Epstein and Markus Hehlen of the Los Alamos National Lab, and Prof. Kevin Malloy from UNM to further this research towards achieving lower temperatures and developing the technology for practical, compact and efficient cryocoolers.

Explore further: New gallium nitride film method beats the heat

More information: To view the paper visit: Laser cooling of solids to cryogenic temperatures -- www.nature.com/nphoton/journal/vaop/ncurrent/full/nphoton.2009.269.html

Related Stories

New gallium nitride film method beats the heat

February 21, 2006

A team of Los Alamos National Laboratory scientists have developed a method for growing crystalline gallium nitride films at lower temperatures than industry standards. By eliminating the higher temperatures and harsh, reactive ...

Towards the magnetic fridge

April 21, 2006

Researchers at the University of Cambridge have discovered a material that gives a whole new complexion to the term 'fridge magnet'. When this alloy is placed in a magnetic field, it gets colder. Karl Sandeman and his co-workers ...

Scientists succeed in cooling solid material with laser

July 26, 2006

A team of researchers at the University of the Basque Country have experimentally demonstrated something that other scientists have been trying to achieve for decades: the cooling of erbium-doped materials with laser light.

Race for better superconductors heats up

October 20, 2008

Scientists have discovered a new family of superconductors -- materials that carry electricity more efficiently than copper and other metals -- whose properties rekindle enthusiasm about the possibility that these exotic ...

Scientists cool gas by laser bombardment

September 2, 2009

Three decades ago, American and Finnish scientists came up with a very powerful method for cooling gases by "laser bombardment." Only now were physicists at the University of Bonn able to demonstrate that it actually works. ...

Recommended for you

CERN collides heavy nuclei at new record high energy

November 25, 2015

The world's most powerful accelerator, the 27 km long Large Hadron Collider (LHC) operating at CERN in Geneva established collisions between lead nuclei, this morning, at the highest energies ever. The LHC has been colliding ...

'Material universe' yields surprising new particle

November 25, 2015

An international team of researchers has predicted the existence of a new type of particle called the type-II Weyl fermion in metallic materials. When subjected to a magnetic field, the materials containing the particle act ...

Exploring the physics of a chocolate fountain

November 24, 2015

A mathematics student has worked out the secrets of how chocolate behaves in a chocolate fountain, answering the age-old question of why the falling 'curtain' of chocolate surprisingly pulls inwards rather than going straight ...


Adjust slider to filter visible comments by rank

Display comments: newest first

not rated yet Jan 19, 2010
Has anyone looked at the applications of these techniques to improve basic refrigerators or heat pumps for homes or businesses? That is, might these techniques be more efficient and/or less expensive at cooling (or possibly heating) than current methods? Or might this be as inefficient as, say, opening your hot oven to heat your home?
not rated yet Jan 19, 2010
dk2009: "Or might this be as inefficient as, say, opening your hot oven to heat your home?"

That's a bad example. The heating efficiency of an electric or gas range is about the same as an electric or gas heater. There are *many* other safety reasons not to do this though.

I think the analogy you're going for is that cooling your house by opening your fridge would be pointless, as the net heat would increase.
not rated yet Jan 20, 2010
Great tech, useful in cooling the walls of thermonuclear fusion reactors, i also envision on the flipside; the potential of laser field interferrometry to catalyze quantum atomic fission for fusion reactor processes.
not rated yet Jan 20, 2010
"Melting point of liquid nitrogen"?? Not sure how a liquid melts:)
On a serious note, the temp of LN2 is also a convenient way to cool to superconducting temperatures so there may be a lot of those kind of applications, for instance, suppose you have a kind of fiber optic cable doped with Ytterbium interacting with a pump laser in such a way as to cool down the fiber, perhaps it can lead to a way to make superconductive electronics or my favorite, superconducting antenna's.
not rated yet Jan 20, 2010
A device like a microwave oven in reverse that quickly chills any hot objects placed in it would be very welcome in the kitchen. Could laser cooling achieve this?

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.