Bistability in the Laser Cooling of Atomic-Beams

We study the resonant interaction of a beam of two-level atoms with two counter-propagating frequency-chirped lasers, showing that the bistable response of the atomic deceleration to the sweeping rate gives origin to a double-peaked pseudo-stationary (PS) velocity distribution that lasts for a time interval which is orders of magnitude longer than the relaxation time to the PS state. Essentially the same response is predicted for a single laser interacting with two atomic transitions.