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**Electron Multiplying CCDs**

An Introduction Simon Tulloch

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**Electron Multiplying CCDs**

Multiplication register Store Area Image Area Normal Serial register Avalanche multiplication takes place in Multiplication Register, using an HV clock (40-45Volts). Multiplication register 1e- in 1000e- signal out Multiplication register Standard MOSFET amplifier Commercially available : CCD x 128 CCD87/ x512 CCD201 1K x 1K

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**Flexible Operation Electron Multiplying Amplifier Conventional Amp.**

E2V CCD201 Electron Multiplying Amplifier Conventional Amp. 3e noise To Observe: Absorption lines Bright Emission Lines Emission lines superimposed on bright continuum clock left clock right <<1e noise To Observe: Faint Emission Lines

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**Multiplication Clocking 1**

In this diagram we see a small section of the gain register Gain electrode Potential Energy

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**Multiplication Clocking 2**

Gain electrode energised. Charge packets accelerated strongly into deep potential well. Energetic electrons loose energy through creation of more charge carriers (analogous to multiplication effects in the dynodes of a photo-multiplier) . Gain electrode Potential Energy Potential Energy

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**Multiplication Clocking 3**

Clocking continues but each time the charge packets pass through the gain electrode, further amplification is produced. Gain per stage is low, <1.015, however the number of stages is high so the total gain can easily exceed 10,000 Potential Energy Potential Energy

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Multiplication Noise Flat fields taken with an EMCCD show unusual statistics. The variance in the flat fields is no longer equal to the mean signal as is expected with photon statistics. Effect is to increase the photon noise by a a factor of

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**EMCCD becomes competitive at lower exposure levels**

With EM Gain: At low illumination, photons are resolved. Without EM Gain: object only just visible above noise. Also visible is the Clock Induced Charge (CIC) which is the dominant noise source (typical value 0.03e-)

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**EMCCD range of operation**

So at higher expsoure levels the EMCCD actually performs worse than a normal CCD EMCCD EMCCD wins due to zero read noise EMCCD loses due to multiplication noise

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**Early EMCCD Demonstrations**

1) Crab Nebula pulsar at 180fps 2) Photon interference in the lab Threshold Cryogenic CCD87 imaging a faint pinhole Raw input frames Thresholded and accumulated Particles? Waves?

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