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Figure 3
Illustration of the SNR advantages afforded by synchronous digitization for low light detection, in which the digitizer is clocked to record the voltage of transients produced by single photons arriving synchronously with the firing of the laser. In the simulation of the raw time-dependent signal streaming from a detector in (a), transient signals are captured at the point of maximum signal-to-noise in synchronous digitization (red arrows). In contrast, asynchronous digitization (blue arrows) at low acquisition rates can miss single-photon events and underestimate photon count rates. Because the current produced from a single-photon absorption event is a random variable, the probability of obtaining a particular peak voltage is described by the peak height distribution, modeled herein by an exponential probability density function. Performing asynchronous digitization as in blue arrows in (a) results in a higher probability of detecting low-voltage transients illustrated in (b), with corresponding reductions in the recovered SNR.

Journal logoJOURNAL OF
SYNCHROTRON
RADIATION
ISSN: 1600-5775
Volume 23| Part 4| July 2016| Pages 959-965
doi:10.1107/S1600577516005919
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