FREQUENCY-DEPENDENT SPECTROSCOPY MEASURES TIME-DEPENDENT PHENOMENA.

A new method for resolution of complex decay kinetics has recently become possible. Instead of excitation of the sample using a brief pulse of light, the sample is excited with light whose intensity is modulated using an electro-optic modulator. How is intensity-modulation useful in the analysis of time-dependent phenomena? The authors rely upon the equivalence of information available in the time and frequency domains. In particular, they measure the phase shift and modulation of the emission, both relative to the incident beam. Once such data are obtained over a range of frequencies they may be used to calculate the decay kinetics of the sample. Generally speaking, the broader the frequency range, the faster the process that can be measured in this way.