Time-resolved and state-selective detection of single freely falling   atoms
  We report on the detection of single, slowly moving Rubidium atoms using laser-induced fluorescence. The atoms move at 3 m/s while they are detected with a time resolution of 60 microseconds. The detection scheme employs a near-resonant laser beam that drives a cycling atomic transition, and a highly efficient mirror setup to focus a large fraction of the fluorescence photons to a photomultiplier tube. It counts on average 20 photons per atom. 
Torsten Bondo, Markus Hennrich, Thomas Legero, Gerhard Rempe, and Axel   Kuhn