Fluorescence spectrum photon correlations

In conclusion, we have presented the Hrst high-resolution heterodyne measurement of the elastic peak in resonance fluorescence of a single ion. At identical experimental parameters we have also measmed antibunching in the photon correlation of the scattered Held. Together, both measurements show that, in the limit of weak excitation, the fluorescence light differs from the excitation radiation in the second-order correlation but not in the first order correlation. However, the elastic component of resonance fluorescence combines an extremely narrow frequency spectrum with antibunched photon statistics, which means that the fluorescence radiation is not second-order coherent as expected from a classical point of view. This apparent contradiction can be explained easily by taking into accoimt the quantum nature of light, since first-order coherence does not imply second-order coherence for quantized fields (19). The heterodyne and the photon correlation measurement are complementary since they emphasize either the classical wave properties or the quantum properties of resonance fluorescence, respectively. 

Figure 36. Lead levels in bone can be measured in vivo using XRF spectroscopy, (a) y-rays or X-rays are used (source) to eject either L-shell electrons (L-XRF) or K-shell electrons (K-XRF) from lead in bone when outer-shell electrons fill this vacancy, photons are released (fluorescence) and are monitored by the detector (10, 523). A typical X-ray fluorescence spectrum [(b), e.g., of a 112 pg Pbg phantom ) provides the number of counts observed as a function of photon energy. Emissions characteristic of lead occur at 72.8 keV (PbKa2), 75.0 keV (PbKoti), and 84.9 keV (Pb Kpi) (436, 523). Measurements on actual samples are correlated with those obtained from standard phantoms made of plaster-of-paris and doped with a known amount of lead to obtain bone lead concentrations in micrograms of Pb per gram (pg Pbg bone). The bone lead levels obtained by this method correlate extremely well with independent measurements of BLL (c). [Parts (a) and (c) adapted from (524). Part ( ) adapted from (436).]...

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