Electron multiplying charge-coupled device

The amplifier stage of an EMCCD consists of a series of multiplication registers which the photo-electrons generated in the CCD pass through successively. The high voltage that is applied to the registers induces further electrons through impact ionization .

An electron-Multiplying charge-coupled device ( English , EMCCD ) - also known as Low Light Level CCD, LLLCCD, L3CCD or Impactron CCD - is a CCD , in which an electron multiplier route implemented directly in front of the output amplifier (therefore the term electron multiplication , in German electron multiplication).

Layout and function

The amplifier section consists of a large number of charge-coupled shift registers. The number of electrons in each shift register is increased by impact ionization , similar to the effect of an avalanche diode. The probability of impact ionization in each stage is relatively small , but since the number of stages is large (typically> 500), the overall gain can be large: one electron at the entrance generates thousands of electrons at the exit. The gain behavior of multiplication registers with many stages and a high overall gain can be approximated well by the following stochastic equation: ${\displaystyle (P<2\%)}$ ${\displaystyle N}$ ${\displaystyle g=(1+P)^{N}}$

${\displaystyle P\left(n\right)={\frac {\left(n-m+1\right)^{m-1}}{\left(m-1\right)!\left(g-1+{\frac {1}{m}}\right)^{m}}}\exp \left(-{\frac {n-m+1}{g-1+{\frac {1}{m}}}}\right)}$ For ${\displaystyle n\geq m~,}$

Probability distribution of the number of electrons exiting the amplifier stage with gain = 1000 for 1–8 entering electrons. The number of exiting electrons is plotted on the abscissa ; the ordinate shows the probability for this number and is represented logarithmically . The results of the empirical formula are shown on this page for comparison .

where the probability of exit electrons with entrance electrons and an overall gain of is. ${\displaystyle P(n)}$ ${\displaystyle n}$ ${\displaystyle m}$ ${\displaystyle g}$

The input noise of the evaluation circuits of CCDs usually has a level of a few tens of electrons, while the signal of EMCCDs is significantly higher than that of normal CCDs due to the amplification. This results in an image recorder with negligible read-out noise. Ultimately, the effective readout noise in the signal-to-noise ratio is smaller by the multiplication factor. This means that even single photons can be detected.

EMCCDs have a similarly high, and sometimes greater, sensitivity than an intensified charge-coupled device (iCCD). For both, however, the gain varies due to the stochastic gain process; the exact amplification of a pixel charge varies from time to time. At high gains (> 30), this fluctuation has the same effect on the signal-to-noise ratio as halving the quantum efficiency . At low lighting intensities (where sensitivity is most important), however, the advantage that is obtained from the lower readout noise prevails. Particularly in applications in which it can be assumed that a pixel contains a maximum of one electron during an exposure, these can be reliably detected. In this way, the number of photons can be determined very precisely by repeated recordings.

Applications

EMCCDs are used, for example, in night vision devices , in astronomical observation and in fluorescence microscopy .

Individual evidence

1. ↑ ^{a b} Paul Jerram; Peter J. Pool; Ray Bell; David J. Burt; Steve Bowring; Simon Spencer; Mike Hazelwood; Ian Moody; Neil Catlett; Philip S. Heyes: The LLLCCD: Low Light Imaging without the need for an intensifier . In: SPIE 4306, p. 178 (2001), doi: 10.1117 / 12.426953
2. ↑ Olivier Daigle; Jean-Luc Gach; Christian Guillaume; Claude Carignan; Philippe Balard; Olivier Boisin: L3CCD results in pure photon-counting mode . In: SPIE 5499, p. 220 (2004), doi: 10.1117 / 12.552411
3. ↑ Jaroslav Hynecek: Impactron-A New Solid State Image Intensifier . In: IEEE Transactions on Electron Devices, vol. 48, issue 10, pp. 2238-2241 (2001), doi: 10.1109 / 16.954460

Web links

• e2v (e2v technologies): Developer of the first EMCCDs (L3Vision), successor to Marconi Applied Technologies, formerly also listed under the name eev (English Electric Valve Company) , in English

• Link to the eev patent from 1998

• Texas Instruments: Developer of the first EMCCDs (Impactron), 2001 , in English

• L3CCD Technology , in English