Posted by
Johannes Helm on
URL: http://confocal-microscopy-list.275.s1.nabble.com/About-GaAsP-and-HyD-detector-s-lifetime-tp7583578p7583580.html
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Good morning,
while I do not want to contradict Davide, who already has sent an
answer to your question, Carlos, I should like to mention that GaAsP
detectors cannot only be destroyed by a large photo current as caused by
too bright of a light source once HV is applied. The photo sensitive
coating on the detection window of these detectors, i.e. the GaAsP
coating, as far as I know, does degrade, and the more rapidly so the
stronger the incident light is. To say it in extreme words: Expose it to
the sun light in Death Valley without any protection and it will be gone
within a short time. Since the coating of the Hybrid detector is the
same as on the GaAsP photomultiplier tubes - the difference between the
detectors solely being the sub-sequent amplification of the signal
generated by the incident photon(s) - even the Hybrid detector does NOT
tolerate strong incident light, even if there is not any voltage for
signal amplification applied.
If one, however, installs the detector(s) on the microscope so that it
is protected against any strong light - e.g. by furnishing any light
source on the microscope, which is not used for acquiring images by
means of the named detectors, with electro mechanical shutters, which
automatically will close whenever there would be any "danger" that light
of these light sources could be incident on the detectors - then the
life time of these detectors can be considerably prolonged.
Example:
Most MPLSM systems - there are exceptions - will include equipment for
wide field epi-fluorescence or transmitted light observation.
There also might be in the turret for the epi-illumination fluorescence
filter "cubes" one position containing a short pass dichroic, which will
transmit the IR light from the laser but reflect any visible light
towards the detector.
If, incidentally, this filter is in the ray path, while at the same
time the stressed and tired PhD student in biology, who quite naturally
is mostly interested in getting the data for her next paper out of her
preparation and does not care so much about laboratory equipment to be
used by the next generation of PhD students, switches on the 12V / 100W
halogen bulb for transmitted light wide field observation, this is a
little bit like the "Death Valley" experience for the detector. One can
avoid that by installing a position detector in the turret and send its
signal to a shutter in front of the 12V / 100W bulb so that the shutter
will close - and remain closed - whenever the turret is not in a "safe"
position (which is NOT the same as "whenever the shutter is in the
"dangerous" position).
Reference e.g. P. J. Helm, T. Reppen, P. Heggelund (2009), A setup for
combined multi photon laser scanning microscopic and multi electrode
patch clamp experiments on brain slices, Proc. SPIE 7183:71832Q-1 -
71832Q-8
Best wishes,
Johannes
On 2015-03-30 08:27, Carlos Sanchez Martin wrote:
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P. Johannes Helm
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