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Detection of slow atoms confined in a Cesium vapor cell by spatially separated pump and probe laser beams

The velocity distribution of atoms in a thermal gas is usually described through a Maxwell-Boltzman distribution of energy, and assumes isotropy. As a consequence, the probability for an atom to leave the surface under an azimuth angle θ should evolve as cos θ, in spite of the fact that there is no microscopic basis to justify such a law. The contribution of atoms moving at a grazing incidence towards or from the surface, i.e. atoms with a small normal velocity, here called "slow" atoms, reveals essential in the development of spectroscopic methods probing a dilute atomic vapor in the vicinity of a surface, enabling a sub-Doppler resolution under a normal incidence irradiation. The probability for such "slow" atoms may be reduced by surface roughness and atom-surface interaction. Here, we describe a method to observe and to count these slow atoms relying on a mechanical discrimination, through spatially separated pump and probe beams. We also report on our experimental progresses toward such a goal.