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Posted: May 17, 2010
Laser cooling of solids for sensitive sensors
(Nanowerk News) The sensors that allow satellites to take measurements are happiest when cold. Mechanical pumps onboard keep sensors' semiconductor elements at temperatures hundreds of degrees below zero. But these cryogenic pumps also produce noisy vibrations that interfere with the collection of data by the sensitive sensors.
Mansoor Sheik-Bahae of the University of New Mexico and colleagues are developing a technique to cool semiconductors loads that would use a vibration-free solid-state technology: laser cooling, which has traditionally been used to lower the temperature of dilute gases but can also cool transparent solids doped with rare-earth ions by kicking out energetic photons (or fluorescence up conversion). In January the group set a record by cooling a crystal down to 155 Kelvin, research published in Nature Photonics. At the upcoming CLEO meeting, Denis Seletskiy, the lead author and a senior graduate student from the group, will describe a new experiment in which the temperature of a GaAs semiconductor load was lowered down to 165 Kelvin, a useful temperature for some kinds of detectors.
"This is the only solid-state technology that can reach these temperatures, the coldest that any semiconductor has gotten without the use of cryogens and/or mechanical coolers," says Sheik-Bahae.
In addition to cutting down on vibrations, this optical refrigeration technique offers a number of other technical advantages. The laser could be guided through an optical fiber to a lightweight cooling head convenient for sensors mounted on delicate gimbals. It could also be used to selectively cool tiny areas of components much too small for other cooling technologies to selectively target.
"Our goal is to try to get colder and colder, to get to 123 Kelvin -- the NIST-defined standard for cryogenic -- and then next to 77 Kelvin, the boiling temperature of liquid nitrogen," says Sheik-Bahae. "With the right laser and the right power, we know we can get to 120 Kelvin."
"The U.S. military is interested in applying this new research," says Sheik-Bahae. "This is quite exciting as this is a young field and more research still remains to be done in parallel to transitioning the mature components to industry. In the long term, the application of this technology to cool superconducting devices is also extremely tantalizing."