Technique that permits @R05206@ of the parameters characterizing a @F02453@ decay. Instead of using an exciting @VT07496@, UV, or @IT07399@ radiation pulse (see @S05689@), the sample is excited by sinusoidally modulated radiation at high @F02525@. The fluoresence response is sinusoidally modulated at the same frequency as, but delayed in phase and partially demodulated with respect to the excitation.
- The modulation ratio is defined as the ratio of the modulation depth (AC/DC ratio) of the @F02453@ and the modulation depth of the excitation. The phase shift and the modulation ratio characterize the harmonic response of the system. These parameters are measured as a function of the modulation frequency. No deconvolution is necessary because the data are directly analysed in the frequency domain.
- Phase and modulation measurements can be done by using either a @CT07348@ (or a @X06699@) and an optical modulator (in general a Pockel cell) or the harmonic content of a pulsed @L03459@.