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Figure 4
(a) Measured intensity distribution of the measured current at the fluorescence APD for 72000 unpumped shots. The lower panel shows a histogram overlaid with a series of Gaussian peaks, each with the same width and an amplitude determined by the probability of a Poisson distribution with a maximum of 5.7 photons. The upper panel shows the residuals of the fit with respect to the measurement. (b) Measured/estimated squared signal-to-noise ratio of the fluorescence difference signal versus the number of shots. These data were extracted from a time scan at the B feature where only data from after time zero to 2 ps are analyzed. The slope indicates 6.8 photons pulse−1, which is well matched to the flux estimate of the increased fluorescence signal after time zero (see text).

Journal logoJOURNAL OF
SYNCHROTRON
RADIATION
ISSN: 1600-5775
Volume 33| Part 5| September 2026|
https://doi.org/10.1107/S1600577526006363
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