Laser detection of single atom fluorescence
Balykin V.I. , Letokhov V.S. , Mishin V.I. , Semchishen V.A.
The intensity of a beam of sodium atoms was measured by a procedure in which the fluorescence signal of a single atom was detected and resolved. The minimum observable flux is 10 atoms/sec, corresponding to 10-4 atoms in the recording region.