An Overview of Photon Counting in EMCCDs
Figure 1 - 'Photon Counting' vs. 'Standard EM-on' Imaging for very weak signals:
Images A, B and C were recorded under identical illumination conditions, identical exposure times and each with EM gain set at x1000. The benefit of Photon Counting under conditions of low Clock Induced Charge (CIC) are evident. Images D and E are derived from a larger number of accumulated images, to yield a greater measurable signal to noise ratio. An identically positioned Region of Interest on each image was used to determine S/N of 3.86 and 6.02 for standard and photon counted images respectively. This factor improvement is in accord with the theory of Photon Counting circumventing the influence of multiplicative noise (noise factor) in EMCCD signals.
Photon Counting in EMCCDs is a way to overcome the multiplicative noise associated with the amplification process, thereby increasing the signal to noise ratio by a factor of root 2 (and doubling the effective Quantum Efficiency of the EMCCD). Only EMCCDs with a low noise floor can perform photon counting. The approach can be further enhanced through innovative ways to post process kinetic data.
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