Optical guiding of atomic fountain by a hollow laser beam

We have performed an experiment to optically guide an atomic fountain by using a cylindrical hollow laser beam (HLB). The atoms are launched upward by using a moving molasses technique with the atomic Zeeman shift. We observe that 0.5 % of the launched atoms are detected without the HLB whereas a tenfold enhancement of the HLB-guided atomic fountain is clearly obtained without appreciable broadening of the time-of-flight signal. Moreover, we calculate the enhancement for various conditions by using Monte-Carlo simulations and study the possibility of applications to the Rb atomic fountain clock.