Trapping and Cooling of Neutral Atoms with the Dipole Force of a Laser Beam

David S. Weiss

Introduction and review of quantum mechanics: Review of Quantum Mechanics.- The Density Matrix.- Force on Two-Level Atoms.- Multi-Level Atoms.- General Properties Concerning Laser Cooling. Cooling and Trapping: Deceleration of an Atomic Beam.- Optical Molasses.- Cooling Below the Doppler Limit.- The Dipole Force.- Magentic Trapping of Neutral Atoms.- Optical Traps for Neutral Atoms.- Evaporative Cooling. Applications: Newtonian Atom Optics.- Ultra-Cold Collisions.- deBrooglie-Wave Optics.- Optical Lattices.- Bose -Einstein Condensation.- Dark States.

Fujio Shimizu

Charles S. Adams, Erling Riis

Olivier Émile, F Bardou, Ch Salomon +3 more

We report on the observation of a new laser trap for neutral atoms. It uses three orthogonal pairs of counterpropagating laser beams having linear polarizations at 45° and a quadrupole magnetic field. 10 8 cesium atoms were thus confined in a 0.15 mm 3 volume at a temperature of 60 μK, a factor of 2 below the Doppler cooling limit. We interpret this trapping as being due to the new magneto-optical force recently observed by Grimm et al. and which is essentially a dipole force rectified by the magnetic field. This trap opens new possibilities for increasing the phase-space density of laser-cooled atoms.

Curtis C. Bradley, Randall G. Hulet

J. Weiner

Atom traps Light forces It is well known that a light beam carries momentum and that the scattering of light by an object produces a force. This property of light was first demonstrated by Frish [139] through the observation of a very small transverse deflection (3 × 10 –5 rad) in a sodium atomic beam exposed to light from a resonance lamp. With the invention of the laser, it became easier to observe effects of this kind because the strength of the force is greatly enhanced by the use of intense and highly directional light fields, as demonstrated by Ashkin [20, 21] with the manipulation of transparent dielectric spheres suspended in water. The results obtained by Frish and Ashkin raised the possibility of using light forces to control the motion of neutral atoms. Although the understanding of light forces acting on atoms was already established by the end of the 1970s, unambiguous demonstration of atom cooling and trapping was not accomplished before the mid 1980s. In this section we discuss some fundamental aspects of light forces and schemes employed to cool and trap neutral atoms. The light force exerted on an atom can be of two types: a dissipative, spontaneous force and a conservative, dipole force. The spontaneous force arises from the impulse experienced by an atom when it absorbs or emits a quantum of photon momentum.