Quantitative Stability in EMCCDs
Figure 1 - iXon Baseline Clamp (bias stability) in operation. A standard feature in iXons since 2002.
EMCCDs are susceptible to various sources of data instability. Each of these sources have been addressed in iXon Ultra and iXon3 to ensure reliable quantitative performance throughout a kinetic acquisition and also repeatability between measurements.
Baseline Clamp
The baseline (or bias level) is an electronic offset added to the output signal from the EMCCD sensor to ensure that the displayed signal level is always a positive number of counts. No actual noise is associated with this positive counts value and thus it is important to recognise that it does not affect sensitivity. However one must remember to subtract the baseline offset value from the signal intensity when performing signal to noise calculations.
Traditionally, when acquiring data, small changes in heat generation of the driving electronics within the detector head may cause some drift in the baseline level. This is often particularly observable during long kinetic series.
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