Laser fluorescence detection of single atoms

Results are presented of investigations aimed at detecting single atoms of sodium by the fluorescence method under conditions of cotrolled cyclic interaction of sodium atoms with a circularly-polarized light wave at a resonant frequency. To obtain multiple interaction of atoms with laser radiation they have been at first optically oriented, as a result of which the atom came to sublevel F=2, msub(F)=2 from which the only transition to the F'=3, msub(F')=3 sublevel is possible. The maximum mean signal from each sodium atom interacting with laser radiation constitutes nsub(max)=2 photoelectrons. The minimum flow of sodium atoms detected during the experiment constitutes equal to approximately 1 atom/s at the probability of atom detection equal to 0.4. In the single atom detection when the fluorescence signal in the center of the photoelectron absorption line anti nsub(f)> 1 the tails of atom spectrum absorption lines were greatly suppressed. A possibility is shown of using this method of suppressing the spectral line tails when detecting low concentrations of atoms of one element against the background of great concentrations of another element for a case when the interval between spectrum absorption lines of these elements is approximately 0.1-100 cm-1