MULTISTABILITY IN THE LASER COOLING OF ATOMIC-BEAMS

We describe the interaction of a beam of two-level atoms with multiple laser beams propagating in the opposite direction. The lasers are fre quency-chirped in order to remain close to resonance and they continuo usly decelerate the atoms by radiation pressure. In a deterministic tr eatment, the average atomic velocity exhibits multistability cycles as a function of the chirping rate. A statistical (Fokker-Planck) treatm ent shows the corresponding splitting of the atomic velocity distribut ion into well-separate, quasi-monokinetic bunches of atoms. In the lab oratory reference frame, multistability shows up through the increasin gly decelerated motion of these atomic bunches. Analytical results are presented, as well as numerical simulations for a beam of cesium atom s, both in the laboratory frame and in the non-inertial frame. The con ditions for the observation of multiple cooling with frequency-chirped lasers are discussed. A comparison with standard chirped cooling is o utlined. Possible applications are indicated.