ABSTRACT
Frequency-domain fluorometers generate the fluorescence with light, which is sinusoidal and modulated at different frequencies depending on the lifetime values to be measured (for nanosecond decays, megahertz), and then they measure the phase shift and amplitude attenuation of the fluorescence emission relative to the phase and amplitude of the exciting light (see Figure 4.1). Thus, each lifetime value will cause a specific phase shift and attenuation at a given frequency. For single-lifetime samples, the lifetime may be calculated directly from either the phase shift or the magnitude of the attenuation (or both because both are available from a single measurement). For multiple lifetimes, many measurements are required over a range of excitation frequencies.
