Posted by
James Pawley on
URL: http://confocal-microscopy-list.275.s1.nabble.com/Upgrading-Leica-MP-PMTs-to-HyD-or-Ga-As-tp7585036p7585050.html
Hi all,
Don’t know anything about the layout of SP2 scan head but it is probably worth remembering a couple of points about hybrid PMTs before you start this process:
1) PMTs usually use power supplies that operate in the range of 500-1,200 volts. Hybrids commonly use 10-20kV.
2) Hybrids are particularly sensitive to being exposed to too much light when under power (every photoelectron arrives at the APD on the anode with an energy of 10-20keV and most of this energy ends up as heat.) So you would have to be very careful to interface the hybrid's power supply with the Leica control electronics in such a way that you could never expose it to too much light.
3) The good news is that, apart from having a photocathode QE that is at least as good as that of the best “normal” PMT (GaAsP?), the first stage gain of the hybrid is so high that the detector has almost no multiplicative noise. This means that its "effective QE” is between 1.5x and 2x better than most normal PMTs with the same type of photocathode.
4) GaAs photocathodes are effective in the red and near-IR because they have a low work function. The downside of this is that they tend to produce a high dark signal unless they are actively cooled. Arranging Peltier cooling (and the power needed for it) can add complexity to what is already a fairly serious project.
5) APDs have such massive multiplicative noise that they must be used in a pulse-counting mode and when used in this way, single-APD detectors are generally not fast enough to cope with the signal rates commonly found in confocals.
This problem is solved with the multi-pixel photon counter (MPPC;
https://www.hamamatsu.com/eu/en/4004.html ) in which the light signal is spread out over an array of 400-1,600 APDs, all connected in parallel. But such detectors have virtually no multiplicative noise and do not require pulse counting but they have a lower fill-factor than a normal APD (reducing its effective QE) and integrating one into an existing instrument would require both cooling and the addition of the optics needed to make sure that the signal light was evenly spread over the entire active area of the device (no matter what pinhole size was used).
Good luck with your modifications. It is hard to exaggerate the importance of having the best photodetector possible.
Best,
Jim Pawley
James and Christine Pawley, 5446 Burley Place, Box 2348, Sechelt BC, Canada, V0N3A0
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[hidden email]>, Phone 1-604-885-0840, cell 1-604-989-6146
On Apr 13, 2016, at 3:49 PM, Rik van Gorsel <
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Ethan,
Photo is of SP5 scan head. Jan is right, if you do multiphoton excitation, it would be a waste of useful photons to pass the light through a pinhole (and all the other optical elements), and it is best to use the RLD port.
- Rik
On 4/13/2016 5:17 PM, Jan Pala wrote:
Dear Ethan,
most probably your SP2 scanhead doesnt have the adaptation for X1 port.
Check this:
http://biology.illinoisstate.edu/images/confocal-schem-ISU.jpgX1 port should be just above pinhole (7) and analyzer wheel (8), i.e.
instead of mirror there should be a modification for X1 port.
The subject of your original post was "Leica MP", i.e. it could be easy to
adapt third party detectors for RLD-NDD port of your multiphoton system.
Best regards,
Jan
On Wed, Apr 13, 2016 at 10:56 PM, Ethan Cohen <
[hidden email]>
wrote:
Rik: Thanks for the useful response.
So I should see some sort of bump on the side of the scan head if I have
this adapter?
My unit does have a C-mount.
Is this a photograph of an SP2 head or SP5 head?
Ethan.
--
Rik van Gorsel, PhD
Boston Electronics Corporation
<
http://www.boselec.com/products/documents/HeimannArrays5-19-11.pdf>