Self-cooling of a micromirror by radiation pressure
Nature, 444 (7115):
67--70 (Nov 2, 2006)DOI: 10.1038/nature05273
Abstract
Cooling of mechanical resonators is currently a popular topic in many
fields of physics including ultra-high precision measurements, detection
of gravitational waves and the study of the transition between classical
and quantum behaviour of a mechanical system. Here we report the
observation of self-cooling of a micromirror by radiation pressure
inside a high-finesse optical cavity. In essence, changes in intensity
in a detuned cavity, as caused by the thermal vibration of the mirror,
provide the mechanism for entropy flow from the mirror's oscillatory
motion to the low-entropy cavity field. The crucial coupling between
radiation and mechanical motion was made possible by producing
free-standing micromirrors of low mass (m\~400ng), high reflectance (more
than 99.6\%) and high mechanical quality (Q\~10,000). We observe cooling
of the mechanical oscillator by a factor of more than 30; that is, from
room temperature to below 10K. In addition to purely photothermal
effects we identify radiation pressure as a relevant mechanism
responsible for the cooling. In contrast with earlier experiments, our
technique does not need any active feedback. We expect that improvements
of our method will permit cooling ratios beyond 1,000 and will thus
possibly enable cooling all the way down to the quantum mechanical
ground state of the micromirror.