An atomic fluorescence transit-time velocimeter

We report the development of an atomic laser velocimeter capable of measuring moderate gas flow speeds. It is based on recording the burst of resonance fluorescence emitted by a single atom as it passes through one or two resonant laser beams. Thus far speeds up to 13 m/s have been successfully measured using single atoms crossing one laser beam. If an average is taken over many atoms, higher velocities can easily be realized. With two laser beams, a flow velocity of 88 m/s has been measured with an integration time of 0.5 s.