Technique that permits recovery
of the parameters characterizing a fluorescence
decay. Instead of using an exciting visible
, or infrared
radiation pulse (see single-photon timing
), the sample is excited by sinusoidally modulated radiation at high frequency
. 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 is defined as the ratio of the modulation
depth (AC/DC ratio) of the fluorescence 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 CW laser (or a xenon lamp) and an optical modulator (in general a Pockel cell) or the harmonic content of a
PAC, 2007, 79, 293
(Glossary of terms used in photochemistry, 3rd edition (IUPAC Recommendations 2006))
on page 346
IUPAC. Compendium of Chemical Terminology, 2nd ed. (the "Gold Book"). Compiled by
A. D. McNaught and A. Wilkinson. Blackwell Scientific Publications, Oxford (1997).
XML on-line corrected version: http://goldbook.iupac.org (2006-) created by M. Nic,
J. Jirat, B. Kosata; updates compiled by A. Jenkins. ISBN 0-9678550-9-8. https://doi.org/10.1351/goldbook