Classic Fluorescence Lifetime Experiments

The intensities of classic lifetime experiments are well within the TCSPC range. Furthermore, sensitivity, time resolution, and accuracy are often more important than short acquisition time. Therefore many classic lifetime systems still use the classic NIM-based TCSPC technique. The general principles of fluorescence lifetime experiments are described in [308, 389], and various fluorescence lifetime spectrometers are commercially available. 

Resonant y-ray absorption is directly connected with nuclear resonance fluorescence. This is the re-emission of a (second) y-ray from the excited state of the absorber nucleus after resonance absorption. The transition back to the ground state occurs with the same mean lifetime t by the emission of a y-ray in an arbitrary direction, or by energy transfer from the nucleus to the K-shell via internal conversion and the ejection of conversion electrons (see footnote 1). Nuclear resonance fluorescence was the basis for the experiments that finally led to R. L. Mossbauer s discovery of nuclear y-resonance in ir ([1-3] in Chap. 1) and is the basis of Mossbauer experiments with synchrotron radiation which can be used instead of y-radiation from classical sources (see Chap. 9). 

This chapter opens with an account of resonance fluorescence and its depolarization by external magnetic fields, a phenomenon now knovm as the Hanle effect. Experiments of this type in mercury vapour are described and we develop a classical theory to explain the shape of the observed signals. This is followed by a discussion of the applications of this technique to the accurate measurement of atomic lifetimes. For the sake of simplicity the effects of interatomic collisions and of trapping or reabsorption of resonance radiation in these experiments are not considered... 

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