2009/06/30 by Ulrich Vogl, Martin Weitz
Engineering · Physics and Astronomy · #Advanced Thermodynamics and Statistical Mechanics #Atomic physics #Laser #Materials science #Optical properties and cooling technologies in crystalline materials #Optics #Physics #Political science #Radiation #Redistribution (election) #Thermal Radiation and Cooling Technologies #cond-mat.quant-gas #physics.atom-ph
paper · pdf · doi:10.1038/nature08203
published as Nature 461, 70 (2009) · 4 figures
openalex publication_date 2009/09/01 · arxiv created 2009/09/24 · arxiv updated 2015/05/13 · openalex created_date 2025/10/10 · openalex updated_date 2026/08/05
The general idea that optical radiation may cool matter was put forward by Pringsheim already in 1929. Doppler cooling of dilute atomic gases is an extremely successful application of this concept, and more recently anti-Stokes cooling in multilevel systems has been explored, culminating in the optical refrigeration of solids. Collisional redistribution of radiation is a proposed different cooling mechanism that involves atomic two-level systems, though experimental investigations in gases with moderate density have so far not reached the cooling regime. Here we experimentally demonstrate laser cooling of an atomic gas based on collisional redistribution of radiation, using rubidium atoms subject to 230 bar of argon buffer gas pressure. The frequent collisions in the ultradense gas transiently shift a far red detuned laser beam into resonance, while spontaneous decay occurs close to the unperturbed atomic resonance frequency. During each excitation cycle, a kinetic energy of order of the thermal energy kB T is extracted from the dense atomic sample. In a proof of principle experiment with a thermally non-isolated sample, we experimentally demonstrate relative cooling by 66 K. The cooled gas has a density of more than 10 orders of magnitude above the typical values in Doppler cooling experiments, and the cooling power reaches 87 mW. Future prospects of the demonstrated effect include studies of supercooling beyond the homogeneous nucleation temperature and optical chillers.