Intensity fluctuation spectroscopy of small numbers of dye molecules in a microcavity

The spontaneous emission from a thin layer of a dilute solution of fluorescent dye molecules within an optical microcavity has been studied. Strong fluctuations in fluorescence intensity are observed when the average number of molecules in the measurement volume is small. We have performed experiments that simultaneously characterize these fluctuations over nine orders of magnitude of time, from ns to s. These measurements have identified photon antibunching characteristic of single-molecule emission, along with triplet-state shelving and diffusion driven number fluctuations. The results give fundamental information on the kinetics of dye molecules and allow one to speculate about the prospect of using single molecules as sources of single photons for quantum optics.