In the September 2017 issue of Nature Photonics, Dr A. Rahman and Professor P. Barker from Physics and Astronomy at UCL report on the first demonstration of optical refrigeration of a submicrometre particle suspended by laser light. The tiny levitated cryostat, consists of a single nanocrystal of Yb3+:YLF crystal cooled to temperatures as cold as −143 °C by illuminating, trapping and aligning it with a single laser beam. Their work has shown that the internal temperature of the nanocrystal can be controlled over a wide range using different trapping laser wavelengths. The laser polarization controls the orientation of the trapped crystal and maximizes its cooling. This development is a further important step towards bringing these macroscopic systems into the quantum regime.
Citation: Laser refrigeration, alignment and rotation of levitated Yb3+:YLF nanocrystals, A.T.M. Anishur Rahman and P. F. Barker, Nature Phonics, Nature Photonics 11, 634–638 (2017)