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Electron Multiplying CCDs An Introduction Simon Tulloch

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Presentation on theme: "Electron Multiplying CCDs An Introduction Simon Tulloch"— Presentation transcript:

1 Electron Multiplying CCDs An Introduction Simon Tulloch

2 CCD x 128 CCD87/97 512x512CCD201 1K x 1K Image Area Store Area Normal Serial register Multiplication register Standard MOSFET amplifier 1e - in 1000e - signal out Avalanche multiplication takes place in Multiplication Register, using an HV clock (40-45Volts). Commercially available : Electron Multiplying CCDs

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

4 Potential Energy Multiplication Clocking 1 Gain electrode In this diagram we see a small section of the gain register

5 Potential Energy Multiplication Clocking 2 Potential Energy 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

6 Potential Energy Multiplication Clocking 3 Potential Energy 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

7 Multiplication Noise Effect is to increase the photon noise by a a factor of 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.

8 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-)

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

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

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