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

In the process of cooling and trapping neutral atoms, we investigate a new laser configuration, which consists of two counterpropagating laser beams with orthogonal u+ and u- polarisations. We show that such a configuration looks more promising than an ordinary standing wave (where the two counterpropagating waves have the same polarisa-tion), and we explain this result as being due to angular momentum conservation which prevents any coherent redistribution of photons between the two waves. Our 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 =O ground state and a J = 1 excited state. 1.