Cooling with light

phys.org | 3/29/2019 | Staff
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ETH researchers have cooled a nanoparticle to a record low temperature, thanks to a sophisticated experimental set-up that uses scattered laser light for cooling. Until now, no one has ever cooled a nanoparticle to such low temperatures in a photon cage. Dominik Windey and René Reimann – a doctoral student and postdoc in the group led by Lukas Novotny, Professor of Photonics – have succeeded in cooling a 140 nanometre glass bead down to a few thousandths of a degree above absolute zero.

The researchers recently published details of their work in the journal Physical Review Letters. Their breakthrough came in the form of a sophisticated experimental set-up involving optical tweezers, whereby a nanoparticle can be made to levitate with the aid of a laser beam. The group has already used the same optical tweezers in previous work, in which they caused a nanoparticle to rotate around its own axis at extremely high speed.

Scientists - Tweezers - Photon - Cage - Cage

The scientists have now supplemented the optical tweezers with a photon cage arranged perpendicular to it. This cage consists of two highly reflective mirrors, whose position the researchers can adjust to within a few billionths of a millimetre.

This precise adjustment is crucial, since the particle scatters part of the laser light and the scientists can use the distance between the mirrors to control which type of light is scattered. "We can adjust the mirrors to scatter more light with a slightly higher frequency than the primary laser light," explains Windey. "As higher-frequency light is also higher in energy, the photons absorb energy from the nanoparticle during scattering." In other words, if the mirror is adjusted correctly, the glass bead loses energy continuously and its oscillation amplitude becomes smaller and smaller: it cools down.

Feature - Set-up - Particle - Oscillation

"The key feature of our experimental set-up is that the particle's oscillation not only becomes smaller...
(Excerpt) Read more at: phys.org
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