Illuminating single molecules in condensed matter

Efficient collection and detection of fluorescence coupled with careful min imization of background from impurities and Raman scattering now enable rou tine optical microscopy and study of single molecules in complex condensed matter environments. This ultimate method for unraveling ensemble averages Leads to the observation of new effects and to direct measurements of stoch astic fluctuations, Experiments at cryogenic temperatures open new directio ns in molecular spectroscopy, quantum optics, and solid-state dynamics. Roo m-temperature investigations apply several techniques (polarization microsc opy, single-molecule imaging, emission time dependence, energy transfer, Li fetime studies, and the Like) to a growing array of biophysical problems wh ere new insight may be gained from direct observations of hidden static and dynamic inhomogeneity.