Researchers cool semi membrane by laser interaction

January 24, 2012 // Nicolas Mokhoff

Researchers at the Niels Bohr Institute, University of Copenhagen, have discovered a new method for laser cooling semiconductor membranes-—by heating the membrane.

Researchers were able to experimentaly cool membrane fluctuations to minus 269 degrees C.

In the experiment a gallium arsenide semiconductor membrane with a thickness of 160 nanometers and a surface area of 1 x 1 mm was made to interact with the laser light in such a way that its mechanical movements affected the light that hit it.

"We carefully examined the physics and discovered that a certain oscillation mode of the membrane cooled from room temperature down to minus 269 degrees C, which was a result of the complex and fascinating interplay between the movement of the membrane, the properties of the semiconductor and the optical resonances,” explained Koji Usami, associate professor at Quantop at the Niels Bohr Institute, in a statement.

The experiment consisted of shining the laser light onto the nanomembrane in a vacuum chamber. When the laser light hits the semiconductor membrane, some of the light is reflected and the light is reflected back again via a mirror in the experiment so that the light flies back and forth in this space and forms an optical resonator. Some of the light is absorbed by the membrane and releases free electrons. The electrons decay and thereby heat the membrane and this gives a thermal expansion. In this way the distance between the membrane and the mirror is constantly changed in the form of a fluctuation, according to Usami.

"The paradox is that even though the membrane as a whole is getting a little bit warmer, the membrane is cooled at a certain oscillation and the cooling can be controlled with laser light," said Usami.

Researchers believe that efficient cooling of mechanical fluctuations of semiconducting nanomembranes by means of light could lead to the development of new sensors for electric current and mechanical forces, and could replace expensive cryogenic cooling used today.

The experiment results are published in the scientific journal, Nature Physics.

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