Posted by
MORONE Diego RIC on
URL: http://confocal-microscopy-list.275.s1.nabble.com/About-GaAsP-and-HyD-detector-s-lifetime-tp7583578p7583581.html
Hi Carlos,
In principle every PMT should have an aging effect depending on strong incident light, so also GaAs detectors. Some companies even go further to consider them as "consumables", to exclude them from maintenance contracts with parts replacement.
Personally, when after 4 years of light/medium usage I changed the GaAs and GaAsP detectors on our multiphoton, I experienced a 30/40 % increase in sensitivity on both types.
have a good monday
Diego
................................
Diego Morone
Microscopy Staff Scientist
Humanitas Clinical and Research Center
Rozzano - Milano, Italy
www.humanitas-research.org
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-----Original Message-----
From: Confocal Microscopy List [mailto:
[hidden email]] On Behalf Of Johannes Helm
Sent: lunedì 30 marzo 2015 09:31
To:
[hidden email]
Subject: Re: About GaAsP and HyD detector's lifetime
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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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