Photon counting histograms fluctuations

Chen Y, Muller JD, So PTC, Gratton E. The photon counting histogram in fluorescence fluctuation spectroscopy. Biophys. J. 

Figure 2.2 Schematic illustration of the conceptual stages in the development of a model to fit photon counting histograms, (a) The case of a non-fluctuating fluorescent particle fixed at the centre of a closed excitation/detection volume (I/q). (b) The case when fluctuations are created by diffusion of the fluorescent molecule around a closed volume with spatially varying excitation/detection efficiency. (c)The case of multiple diffusing molecules in the closed volume, (d) The case when molecules can enter and leave the volume, (e) The case when molecules with different molecular brightness can enter and leave the volume.

Figure 3.17 Photon count histogram of an ideal scatterer placed at the laser focus. The collected photon count distribution (circles, normalized) is fitted exactly by a Poissonian function (line) indicating that there are no fluctuations in the detected signal arising from instability of the light source or other instrumentation.

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