A time-resolved, fluorescence spectrometer makes use of a RadiaLight.RTM. optical switch and no dispersive optical elements (DOE) like gratings. The structure is unique in its compactness and simplicity of operation. In one embodiment, the spectrometer makes use of only one photo-detector and an efficient linear regression algorithm. The structure offers a time resolution, for multiple species measurements, of less than 1 s. The structure can also be used to perform fluorescence correlation spectroscopy and fluorescence cross-correlation spectroscopy.