Abstract: Fluorescence, spectroscopy is used to analyze small numbers of molecules that are present in a relatively small detection volume or zone. Information regarding physical and chemical properties of these molecules is determined by rapidly modulating the wavelength, intensity and/or polarization of laser energy to excite fluorophores that are attached either to the molecule of interest or a molecule that interacts with the molecule of interest. The emission profile of the fluorophores is used to determine useful information about the labeled and/or non-labeled molecules including molecular interactions between the molecules.