EMCCD Tutorial
Q6 Is cooling of EMCCDs important?
The fundamental answer is that if you want to get the best sensitivity from an EMCCD,
it requires effective thermoelectric TE cooling. In EMCCDs, thermal electrons are
amplified in the gain register, just as photo-electrons (signal). As such, when
EM gain is applied even single thermally generated electrons can be seen as a single
pixel noise spike, amplified clear of the read noise floor. Thus, EMCCDs are particularly
sensitive to dark signal. In some applications, such as widefield fluorescence microscopy,
the photon background is sufficiently high that the amplified dark signal contributes
less so to the overall background and cooling is less important. For such applications
a ‘tier 2’ low-cost EMCCD with limited cooling can still be very effectively utilized,
since it is still fundamentally important to eliminate the read noise contribution.
However, in optical configurations such as TIRF microscopy, confocal microscopy
or luminescence detection, where background photons have been minimized, deep TE
cooling of a ‘higher-end’ EMCCD becomes critical, otherwise sensitivity will e sacrificed.
It is a myth that deep cooling is not necessary under conditions of short exposure
times (significant darkcurrent is generated during the readout process alone, irrespective
of exposure time), as can be proven in simple tests. In fact, Andor have defined
a new specification the iXonEM+ spec sheets to reflect the importance
of minimizing darkcurrent events. This specification is based on ability to count
the number of amplified background ‘dark events’ under light tight conditions at
high EM gain setting, employing a short exposure time (30ms). Cooling makes a critical
difference to this value.
Click here to access tech
brief on the importance of cooling technology in EMCCDs. We can prove it!
Following on from a successful chilli campaign, Andor has once again gone down the
‘hot technology’ road, except this time it is with an even more eye catching frozen
chilli. This specially commissioned ad portrays a chilli frozen into a block of
ice. It took 3 days to slow cool the ice to prevent it frosting over. Quirky yes,
but it does get the message across that effective cooling is fundamentally necessary
in EMCCDs to minimize the detection limit, whether short or long exposures are employed.