Sub-poissonian statistics of fluorescence photons of a single molecule

The method previously used by the author for the measurement and calculation of the distribution function w (N)(T)of fluorescence photons from a single two-level atom that is continuously excited by laser light and has a unity fluorescence quantum yield is generalized to the case of a single molecule whose fluorescence quantum yield is smaller than unity and to the case of a three-level molecule whose fluorescence is blinking. The functions w (N)(T) calculated for these two cases demonstrate a sub-Poissonian distribution of fluorescence photons.