ACQUIRING DATA
iKon-L SECTION 5
Page 73
Photon Counting is a technique used to record very low-level signals that might otherwise be lost in
background noise.
When the photon flux is low, Photon Counting can be utilized. By ‘low’ we mean that there is little chance that
two photons will arrive at the same pixel (or binned set of pixels) in the same readout period. In photon
counting mode the CCD is continuously readout without any gaps between scans (so that no signal is lost). If
a ‘spike’, corresponding to a single photon, is detected above the set threshold level then it is counted as a
single event and a 1 is added in memory corresponding to that pixel position.
As the CCD is continually scanned, the signal builds up in memory and can be viewed live on the screen. The
following traces demonstrate the dramatic improvements that are possible from this measurement method.
In order to select the Photon Counting option, activate the Enable tick box in the Photon Counting area of
the Setup Acquisition dialog box.
A suitable threshold level must be chosen, above which any spikes arising can be counted as a single event.
Examples are shown in figures 14 & 15 on the next page.
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