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Dear all,
I, too, do not wish this site to turn into a commercial forum, and so far so 
good.  Given the current level of this discussion, I see no reason why 
commercial concerns cannot discuss and compare their technology with others 
of the same ilk.  The danger is, as Colin admitted near the end of his 
comments, the temptation to extend technology-speak to selling-speak.

As long as the dialog is data-driven, I appreciate the opportunity to see 
direct comparisons between competing technologies.  Where else are you going 
to find immediate give and take for these topics?  Certainly not at a 
demonstration of one instrument.  Maybe it would be useful to have an 
occasional "debate" at major meetings, with panel members from competing 
firms, presenting their hardware in an objective, rigorous manner, comparing 
like specifications using standardized tests.  Pretty naive, eh?

Best regards,
Carl

Carl A. Boswell, Ph.D.
Molecular and Cellular Biology
University of Arizona
520-954-7053
FAX 520-621-3709
----- Original Message ----- 
From: "Colin Coates" <[log in to unmask]>
To: <[log in to unmask]>
Sent: Tuesday, October 17, 2006 4:15 AM
Subject: Re: Commercial Announcement: Quantitative EMCCD technology


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Dear George,

I also wanted to respond to your question that you posed to Karl from
Roper.
I was in a way saddened to see this excellent scientific site being used
for a product launch. While I am highly reluctant to see this forum being
turned into a commercial combat arena, I now feel compelled to input into
the debate which Roper have seen fit to initiate, and make sure the high-
end efforts of other EMCCD manufacturers have been more fairly
represented. Especially as I think you have been misled with a
scientifically unsound treatment of your query.
So let me try to at least remain faithful to the scientific nature of this
site and address this aspect of what was claimed with an injection of
technical reality….

DARKCURRENT VS CIC
It is entirely justifiable to be concerned with minimizing Clock Induced
Charge (CIC), also known as Spurious Noise. This point on its own is fine,
and one that Andor have in fact addressed quite some time ago with our
advanced clocking solutions. However, contrary to what was claimed, the
CIC minimization point is in fact relevant only for  DEEP COOLED EMCCDS,
such as the vacuum TE cooled iXonEM+.
Are Roper saying that the QuantEM will outperform their own deeper-cooled
Cascade II 512B, because the Cascade II has higher CIC?? I stand also in
defense of the new deeper-cooled Hamamatsu C9100-13 system in this regard,
although I cannot comment on Hamamatsu’s treatment of the remaining CIC.

Since Roper have been unable to offer cooling below -30 0C with the
QuantEM, I strongly suspect that the level of amplified darkcurrent
electrons vastly exceeds the level of CIC (unless the Roper CIC levels
were extremely high to start with) – even with short exposures! That is
much more likely to be the primary source of speckled background in their
system.
Andor have proven this in the past with this very 512x512 CCD97 sensor, by
showing EM-amplified darkcurrent events at x1000 EM gain @ temperatures
of -30C, -50C and -80C using 30ms exposures. When you do not cool
effectively (i.e. -30 C), the amplified noise floor is a forest of
darkcurrent spikes and the contribution of CIC is the least of your
concerns – this is not at all suitable for demanding applications such as
confocal microscopy. The beauty of EMCCDs in low photon background set-ups
like confocal, is that they can potentially measure ‘zero’ very well, as
Jim Pawley was very quick to recognize in the ‘early days’ of EMCCD.
However, this capability is much less likely if you do not cool the sensor
sufficiently. It is when you push down towards -80 C that the remaining
CIC (which has been now shown to be temperature independent) becomes the
true detection limit.
How would Roper separate CIC from darkcurrent at such relatively high
temperatures? Is that why they do not quote a CIC spec in the spec sheet?
Andor have several customers around the world using our iXon/iXon+ cameras
for single photon counting – something we have shown you can only do when
both darkcurrent and CIC have been minimized.

HOW TO MEANINGFULLY COMPARE EMCCDS
The method for comparing sensitivity from the same EMCCD sensor (in this
case the very popular E2V CCD97 512x512 back-illuminated sensor) in
cameras from different manufacturers is quite simple, and you don’t even
need a sample. Since the same sensor is used, the QE will essentially be
the same (as long as the manufacturer uses only one input window) and the
read noise floor is overcome through the EM effect.
In terms of sensitivity performance, all that remains is to compare how
well the respective manufacturers have reduced remaining dark events
(darkcurrent and CIC), both of which will be manifest in an intensity
profile as electron spikes amplified clear of the read noise floor.
Just screw a threaded cap onto the c-mount to make sure there are no
photons getting to the sensor, turn up the EM gain to x1000 and take, say
a 30ms image. Notice I don’t even ask you take an especially long
exposure – significant darkcurrent can be generated during the readout
process alone. Take a line intensity profile across any row of 512 pixels
and count the typical number of amplified spikes across that row.
That gives you a feel for the remaining detection limit of that EMCCD.
I urge anyone looking at high-end EMCCD technology to make sure they
insist on such a demonstration.

Beyond this simple sensitivity comparison, look to the fundamental
differences concerning the housing of the sensor. What surprises me more
than any of the ‘new’ claims made, is that people are still buying
backfilled systems housing back-illuminated sensors; BI sensors will
degrade unless all moisture and hydrocarbons are permanently eliminated,
and if you can ensure such elimination then a permanent vacuum is easy, as
is deep cooling. It was these compelling reasons that drove Andor to
develop permanent vacuum technology over 10 years ago.
Vacuum protection also means we can get away with only one input window,
AR coated on each side – i.e. the sensor QE curve on the spec sheet is
what you get in reality. A non-vacuum back-filled camera is much less
protected against these degrading influences, and you would be ill-advised
not to have an extra protective window in front of the sensor. So, for
these reasons such a non-vacuum (o-ring seal, back-filled with inert gas)
system cannot be considered in the same teir 1 EMCCD category as the Andor
iXon/iXon+ or even the Hamamatsu C9100-13 (about which you originally
asked).

For anyone else reading this who is thinking of using EMCCD technology, an
Andor demo is pretty much all we are asking suggest. I am not requiring
you to immediately believe everything I say while I am casting doubt on
the assertions of someone else. I simply ask that you let us prove our
claims.
Andor pioneered the first scientific EMCCD cameras and have been at this
game for much longer than anyone else. We have consistently stayed several
steps ahead of the nearest EMCCD competitors – check out the web site
www.andor.com for our complete EMCCD line-up and overview of their
capabilities. You will see that for quite some time our high-end
iXon/iXon+ solutions have used innovations such as our Baseline Clamp
(i.e. stable bias over kinetic series or EM gain changes), RealGain (real
and linearized gain control), EMCAL (patent-pending user initiated
recalibration of EM Gain – don’t even need a light source) and Anti-Ageing
technology.
Apologies, this is turning into a plug too!

Anyway, that’s about all you will hear from me on the matter – I don’t
wish to clog up this forum any further with commercial righteousness.

Best Regards,

Colin Coates, PhD
Senior Scientist
Andor Technology Plc.

P.S. For those who feel inclined to read further and find out more about
what Andor have pioneered in this technology area, go to www.emccd.com
home page  -  ‘imitation is the sincerest form of flattery’!