A time-resolved spectroscopy system employing a time-division multiplexing optical device with no dispersive optical elements to perform lifetime and concentration measurements in multi-species samples, is disclosed. Some examples include fluorescence and cavity ring-down spectroscopy. The system is unique in its compactness and simplicity of operation. In one embodiment, the system makes use of only one photo-detector and an efficient linear regression algorithm. The system offers a measurement time for multiple species measurements of less than 1 s. The system can also be used to perform fluorescence correlation spectroscopy and fluorescence cross-correlation spectroscopy. Four methods to de-convolve a multi-component, exponentially decaying optical signal such as obtained with the system disclosed here, are presented. These methods may be applied to the measurement of fluorescence decay lifetimes and cavity ring-down times, the latter used extensively for the measurement of gas and trace-gas concentrations in complex mixtures, via absorption spectroscopy.