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![[Figure 3]](cn5052fig3mag.jpg)
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Figure 3
(a) Oscilloscope trace of the preamplified signal of an individual channel of the APD for a primary intensity of I0 ≃ 6 × 107 photons s−1 (detected photons) along with a histogram of the peak pulse height (plotted in brown). Experiments have been performed at a photon energy of E = 18 keV during the PETRA III 240-bunch mode (fb ≃ 31 MHz). Individual photon population numbers can clearly be distinguished in the pulse-height histogram. Pulse widths are τ ≤ 30 ns in all cases. (b) By scanning the delay ts between the signal provided by the PETRA III bunchclock and the sampling instant of the ADC, the QAPD can be used for equivalent time sampling of the preamplified signal. In this mode, individual data points correspond to an average over N ≃ 5.2 × 105 iterations (accumulation time 0.1 s per point at fb ≃ 5.2 MHz). The optimal sampling instant ts is given by the maximum pulse height. It was found that, contrary to the initial expectations, the pulse width does not depend on the number of simultaneously detected photons. Measurements have been performed at a photon energy of E = 18 keV during the PETRA III 40-bunch mode. |
![[Figure 3]](cn5052fig3.jpg)
 | JOURNAL OF SYNCHROTRON RADIATION |
ISSN: 1600-5775
