Researchers at the Niels Bohr Institute of the University of Copenhagen have succeeded in using the heating action of lasers to actively cool a semiconductor. The phenomenon is achieved using a special gallium arsenide (GaAs) semiconductor membrane paired with mirrors to create an optical resonance chamber. When laser light is shot at the membrane, most of it bounces off, is reflected back by the mirror, and then resonates between the mirror and the GaAs surface.
Then the magic happens. Sometimes an atom in the membrane will absorb a photon of light, creating heat and a tiny bit of expansion. The movement of the membrane, the properties of the semiconductor, and the resonant frequencies then interact in a bizarre and wonderful way that cancels the molecular motion generated by heat, ultimately cooling the material to minus 269 degrees C. Although still in the experimental phase, this technique could be useful for cooling electrical components in super-sensitive sensors where thermal energy (as small as it is) creates more noise than the signal being detected. The results of the experiment are published in the January 2012 issue of Nature Physics.