Hamburg 2009 – wissenschaftliches Programm
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A: Fachverband Atomphysik
A 7: Ultracold atoms I: Traps and cooling (with Q)
A 7.4: Vortrag
Dienstag, 3. März 2009, 11:15–11:30, Audi-B
Laser cooling by collisional redistribution of fluorescence — •Ulrich Vogl and Martin Weitz — Institut für Angewandte Physik, Wegelerstraße 8, 53115 Bonn
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 fluorescence cooling in multilevel systems has been explored, culminating in the optical refrigeration of solids. Collisional redistribution of fluorescence is a proposed different cooling mechanism that involves atomic two-level systems, though experimental investigations in gases with moderate density have so far reached the cooling regime. Here we experimentally demonstrate cooling of an atomic gas based on collisional redistribution of fluorescence, using rubidium atoms subject to several hundreds of bars of 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 kBT is extracted from the dense atomic sample. In a proof of principle experiment with a thermally not isolated sample, we experimentally demonstrate relative cooling by 33 K. The cooled gas has a density of more than 10 orders of magnitude above the typical values in Doppler cooling experiments. Future prospects of the demonstrated technique can include cryocoolers and the study of homogeneous nucleation in saturated vapour.