EMCCD Lecture

RIT Center for Detectors published a nice EMCCD lecture by Craig Mackay, Institute of Astronomy, University of Cambridge, UK. The lecture covers main principles and applications of EMCCDs, primarily produced by e2v. Some slides from the lecture:

Introduction to EMCCDs: General Characteristics

• EMCCDs are standard CCDs plus an electron multiplication stage.
• EMCCDs may be read out at high pixel rates (up to 30 MHz for E2V EMCCDs, probably up to 60 MHz for TI EMCCDs).
• The gain mechanism increases the variance in the output signal so that the signal-to-noise ratio goes as √(2N) rather than √(N).
• Equivalent to halving the detective quantum efficiency.
• Photon counting can substantially restore this effective loss in quantum efficiency.
• Clock induced charge (CIC) affects all CCDs, but you will only really notice it with high gain EMCCDs.

When Should You Use EMCCDs?

• Any time that you are really limited by readout noise.
• This is more likely to be the case when running with high pixel rates. Conventional CCDs give excellent read noise but only at low read-out rates.
• Recent developments in sCMOS technology are changing this by offering low read-out noise (~1-2 electrons) and 100 Hz frame rates, though best in rolling shutter mode.
• However, do not forget the equivalent loss in detector quantum efficiency using an EMCCD in analog mode.
• At the lowest signal levels, photon counting gives close to the theoretical full DQE at high frame rates.

EMCCD Ageing

• Illuminating the image area to saturation and running the device at a gain of 1000x will cause the device to fail within a few hours.
• In practice these devices will be used at much lower illumination levels.
• With reasonable care in system design, many years of operation will be obtained.
• The ageing effect is seen as an increase in the high-voltage (multiplication) clock level needed to achieve a specific gain.
• At low gains (gains of a few) no ageing is seen.
• Increasing the gain from 100x to 1000x roughly doubles the short-term ageing rate with little effect on the longterm ageing.
• The ageing is principally caused by excessive signal levels in the multiplication register.
• An increase of 5 V over the life of the device is about the limit before failure occurs.