Calculating Dynamic Range in EMCCDs

Calculating dynamic range in EMCCDs has often been a source of confusion, due to the additional requirement to factor in EM gain and the extended well capacity of the gain register. High dynamic range can be accessed in EMCCDs with careful fine tuning of EM gain.

Dynamic Range (DR) is given by: DR = Full well capacity + Detection limit

Calculating Dynamic Range in an EMCCD camera is a slightly more complicated story than for conventional CCDs. This is because of the favourable effect of EM gain on the detection limit vs. the limiting effect of EM gain on the full well capacity. The easiest way to address this is to first take each parameter separately:

Detection Limit and EM gain

The main function of EMCCD is to eliminate the read noise detection limit and enable detection of weak photon signals that would otherwise be lost within this noise floor. With EM gain, the detection limit is given by the 'Effective Read Noise', i.e. the read noise divided by the gain multiplication, down to one electron. Why never less than one? 

This stems from the definition of detection limit, which is essentially "the signal equal to the lowest noise level". Since you can't get a signal less than one photon, then the detection limit should never be taken as less than one electron.

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