Optical molasses

Summary form only given, as follows. A three-dimensional configuration of counterpropagating laser beams tuned slightly below an atomic resonance frequency can provide strong ´viscous´ damping of the atomic kinetic motion through the action of then photon momentum. This ´optical molasses´, first observed in experiments at Bell Labs, not only cools the atoms to microkelvin temperatures, but also provides confinement and concentration as well. Experiments at NIST in Gaithersburg showed that the temperatures reached in optical molasses were much lower than believed possible on the basis of simple and widely accepted theoretical models. Groups at Stanford University and at Ecole Normale Superieure in Paris both confirmed these experiments and offered novel theoretical models to explain the low temperatures. These models have been qualitatively verified in further experiments at all three laboratories. Experiments with cesium atoms in optical molasses at the Ecole Normale laboratory have found temperatures as low as 5 mu K. It corresponds to an RMS velocity of less than 2 cm/s. Such slow atoms may have important applications in a variety of measurements, including atomic frequency standards where atomic motion is the major factor limiting performance.<>