Doughnut-beam-induced Sisyphus cooling in atomic guiding and collimation

We propose a simple atomic-beam collimator consisting of a blue-detuned cylindrical-hollow (doughnut) laser beam. Cold atoms from a magneto-optical trap are loaded into the doughnut beam and guided in the propagation direction of the doughnut beam. The cold atoms experience efficient Sisyphus cooling induced by the doughnut beam and a weak repumping beam and are collimated in the transverse direction. In the longitudinal direction the cold atoms experience small accelerations that are due to the absorption-induced heating of the doughnut beam and the repumping beam. The cooling, heating, and loss mechanisms in this atomic collimator are analyzed. Our study shows that an intense cold atomic beam with a minimum transverse velocity of ∼2 cm s^−1 (a minimum transverse temperature of ∼1.4 μK) and a brightness of approximately 2×10^13 atoms (sr^−1 cm^−2 s^−1) can be obtained from the collimator.