Cooling of sodium atoms by laser resonance radiation

V. I. Balykin, Vladilen S Letokhov, V.I. Mishin

V. I. Balykin, Vladilen S Letokhov, V. I. Mushin

Arthur L. Robinson

Vasily V. Balashov, Alexei N. Grum-Grzhimailo, V. Zhadamba

William D. Phillips, John V. Prodan, Harold J. Metcalf

Atoms in a thermal beam can be cooled, decelerated, and stopped using the radiation pressure from a nearly resonant laser beam. Several groups have already used this laser-cooling process on an atomic sodium beam. The techniques and results of the various experimental groups are reviewed, and applications of laser-cooled atoms, in particular the possibility of confining them in electromagnetic traps, are discussed.

Leo W. Hollberg, Steven Chu, John E. Bjorkholm +2 more

Using six optical beams (+ and − directions on three orthogonal axes) tuned slightly to the red of resonance it is possible to cool sodium atoms to a few hundred microkelvin. The cooling occurs because the laser radiation pressure creates a damping force which reduces the atomic velocities to a rms value of ~60 cm/s, determined by random scattering. In this optical molasses, the laser beams propagate in all directions and the light acts as a viscous photon fluid which damps the atomic velocity. The resulting motion of the sodium atoms is diffusive until the atoms reach the edge of the laser beams where they escape. The process of atomic confinement by optical molasses can be modeled as a random walk in a viscous medium with a boundary. For a spherical volume of 0.2 cm3 the resulting confinement time is ~0.1 s for half of the atoms to escape. Direct time-of-flight measurement of the atomic temperature gives ~240 μK, which agrees with predictions of quantum limited cooling by resonance radiation pressure. With confinement times of 0.1 s and temperatures of ~240 μK this method provides a source of atoms sufficiently slow for even the highest resolution optical spectroscopy, collision studies, or optical traps.