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Journal of Physics B Atomic and Molecular Physics

Potentialities of a new σ+-σ-laser configuration for radiative cooling and trapping

Jean Dalibard, Serge Reynaud, Claude N. Cohen-Tannoudji

Published Nov 28, 1984• 66 citations
Publisher

Abstract

In the process of cooling and trapping neutral atoms, the authors investigate a new laser configuration, which consists of two counterpropagating laser beams with orthogonal sigma + and sigma - polarisations. They show that such a configuration looks more promising than an ordinary standing wave (where the two counterpropagating waves have the same polarisation), and they explain this result as being due to angular momentum conservation which prevents any coherent redistribution of photons between the two waves. The authors' conclusions are based on a quantitative calculation of the various parameters (potential depth, friction coefficient, diffusion coefficient) describing the mean value and the fluctuations of the radiative forces experienced, in such a laser configuration, by an atom with a J=0 ground state and a J=1 excited state.

DOI
10.1088/0022-3700/17/22/018

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The authors discuss the radiation force in a one-dimensional sigma + - sigma - laser standing wave, for transitions J to J+ Delta J, for any J. and Delta J=+or-1.0. in the limit of low saturation of the atomic transition. The interaction between the radiation field and the atom produces a motion-induced orientation of the atomic ground state which grows rapidly with J. The radiative force on the atom is sensitive to this orientation. For J to J+1 the dissipative part of the total force is much larger than the reactive part, at low velocities, while for the other cases the two contributions are roughly equal and opposite. By using a simple method of calculation, the authors gain much physical insight into the mechanism of induced orientation, and give quantitative results for the size of the radiation force, including both the low-velocity friction coefficient and the velocity capture range.
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We present a new scheme for ID subrecoil laser cooling by velocity-selective coherent population trapping of even-even isotopes of elements found in the second group of the periodical table, particularily, zaaHg and 40Ca. The scheme envolves the transitions (a) between the ground state with the total angular momentum Pg = 0 and the excited one with Fe = 1, @) between the latter state and the second excited one with Fe* = 2. The second transition belongs to the infrared region and has a width much smaller than the transition from the ground state. The lower transition is driven by two counterpropagating o+ and U- polarized running waves. The laser beam applied in the perpendicular direction is a linearily polarized standing wave exciting the