Progress towards a dense atomic beam

W. Grüebler

Stephan Jennewein, Mondher Besbes, Nick J. Schilder +6 more

We measure the coherent scattering of light by a cloud of laser-cooled atoms with a size comparable to the wavelength of light. By interfering a laser beam tuned near an atomic resonance with the field scattered by the atoms, we observe a resonance with a redshift, a broadening, and a saturation of the extinction for increasing atom numbers. We attribute these features to enhanced light-induced dipole-dipole interactions in a cold, dense atomic ensemble that result in a failure of standard predictions such as the "cooperative Lamb shift". The description of the atomic cloud by a mean-field model based on the Lorentz-Lorenz formula that ignores scattering events where light is scattered recurrently by the same atom and by a microscopic discrete dipole model that incorporates these effects lead to progressively closer agreement with the observations, despite remaining differences.

Heinrich Gerhard Kuhn

Tosi, Paolo, Bassi, Davide

V. Danilov Ornl

The excitation of atomic levels due to interaction with electromagnetic waves became of interest in accelerator physics in relation to high efficiency charge exchange injection into rings for high beam power applications. Usually, the beam density is so small that its influence on the wave is completely neglected. Here we consider the case of dense beams - the beam dimensions are large as compared to light reflection length. This paper shows that the waves can be trapped in the medium under these conditions. Moreover, the atoms with induced dipole moments start to interact strongly with each other, leading to possibility to create some atomic patterns when the medium is relatively cold.

Keith Bonin, W. Happer

We have been working on the development of a technique for determining the static polarizabilities of refractory metal atoms. The technique involves producing a dense, cold atomic beam (n {approx equal}10{sup 11} {minus} 10{sup 12} atoms/cm{sup 3}, T {perpendicular} {approx equal} 5 mK) that is illuminated for a short time by a standing wave formed by a Nd:YAG laser. This technique would have an impact on laser isotope separation, ion mobility physics, and theoretical atomic physics. The interaction between the atoms and the laser light results in velocity kicks to the atoms along the two directions defined by the photons in the laser standing wave. The velocity kicks force the atoms to form into planes of alternating high and low density downstream. By Bragg scattering near-resonant light off these planes the static polarizability can be determined. The velocity kicks will also cause the atomic density distribution further downstream to take on a bimodal appearance. A measurement of the separation of the peaks of this distribution can be used to determine the polarizability. Here we report our progress on this technique and the present status of the experiments. A new method for producing focused beams of neutrals, ions, and clusters usingmore » two-stage laser ablation has been developed as a result of our experiments. 7 refs., 12 figs.« less