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AIP conference proceedings

Trapping atoms with radiation pressure

David E. Pritchard, Eric L. Raab

Published Jan 1, 1987• 1 citation
Publisher

Abstract

We show that the optical Earnshaw theorem does not always apply to atoms and that it is possible to confine atoms using spontaneous light forces produced by static laser beams. A necessary condition for such traps is that the atomic transition rate is not a function of the light intensity only. We give general approaches which satisfy this condition and present a new trap design utilizing these principles. This trap has a depth on the order of a kelvin and a volume of several cm3.

DOI
10.1063/1.36785

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Annual Meeting Optical Society of America•Jan 1, 1987•0 citations
We show that the optical Earnshaw theorem does not always apply to atoms and that it is possible to confine atoms using spontaneous light forces produced by static laser beams. A necessary condition for such traps is that the atomic transition rate is not a function of the light intensity only. We give general approaches which satisfy this condition and present a new trap design utilizing these principles. This trap has a depth on the order of a kelvin and a volume of several cm3.
We show that the optical Earnshaw theorem does not always apply to atoms and that it is possible to confine atoms by spontaneous light forces produced by static laser beams. A necessary condition for such traps is that the atomic transition rate cannot depend only on the light intensity. We give several general approaches by which this condition can be met and present a number of specific trap designs illustrating these approaches. These traps have depths on the order of a kelvin and volumes of several cubic centimeters.
We propose several ideas for neutral atom traps which utilize spontaneous light forces produced by static laser beams. Although the “optical Earnshaw theorem”1 would seem to prohibit such traps, the theorem does not apply if the proportionality constant between force and light intensity is made to vary with position. We suggest possible ways to accomplish this: Zeeman tuning the atom’s resonant frequency by applying a changing magnetic field; varying the quantization axis of the system via a magnetic field cork-screw; utilizing optical pumping effects which arise from matrix element imbalances between hyperfine sublevels in certain atoms. These traps are true in the sense that they provide a potential energy minimum in three dimensions, as well as dissipative cooling. Compared with gradient force light traps, these traps are many times deeper, a million times larger, and can be operated cw.
Radiation pressure forces have been proposed for making stable optical traps for neutral atoms and other dielectric particles. Recently introduced optodynamic or alternating beam traps based on the scattering force are compared with cw traps based on the gradient force. Trapping experiments on micron-sized dielectric particles are described which demonstrate the basic principles of alternating beam light trapping. The relationship of these traps to the optical Earnshaw theorem is considered. The implications for trapping of recently demonstrated sources of slow atoms are also discussed.
There has been considerable activity recently on cooling and trapping atoms using laser light. This work raises expectations that laser manipulation of atoms will be an important new tool for atomic physics. However, up to now, almost all the work has been on sodium atoms using light from dye lasers. The expense and complication of a narrowband dye laser system is a considerable limitation on the possible uses of this tool. In response to this we have been exploring the use of inexpensive diode lasers for the manipulation of atoms. We have found that diode lasers work very well for this purpose and even have some advantages over dye lasers in addition to cost and ease of use. We previously reported using light from diode lasers to stop a beam of atomic cesium. Here we discuss our more recent work using diode lasers to produce extremely cold cesium vapor via optical molasses cooling and the demonstration of a new type of optical trap. This is a purely optical spontaneous force trap which uses spatially inhomogeneous optical pumping to circumvent the optical Earnshaw theorem.