Model labels: DetChannelAssby:1, DetChannelAssby:2
Assembly instructions
Oil method
PMT assembly
The goal is to couple the lens onto the PMT face with oil
Seal around the edge of the window that is on top of the PMT photocathode, so that oil can not leak into the body of the PMT, with 5 min epoxy. Be careful not to soil the plate above the photocathode.
Add 30 - 50 ul of microscope immersion oil.
Place condensor lens on oil–touch to oil on one side first so as not to trap large bubble underneath. Make sure there are no bubbles and carefully remove overflow oil from the housing.
Place a thin ring of Kwik-Sil (WPI) on the PMT housing around the lens
Add PMTMountPlate before Kwik-Sil sets, such that sealant squishes between the lens and PMTMountPlate. Hold lens down so that it does not move up while mount plate is being pushed down. Attach PMTMountPlate to PMT with two M3 screws.
Allow ~30 minutes at least for Kwik-Sil to set (oil mixing with Kwik-Sil will interfere with the setting process).
Hold PMT in vise with window side down for several minutes to check if there is oil leakage. Blow gently around seal with canned air to see if there is movement of liquids/uncured Kwik-Sil.
If there is leakage, seal further between the condenser lens and PMTMountPlate using epoxy, or other sealant. It is OK if the sealant touches the face of the condenser lens a couple mm above where this lens meets the edge of the PMT mount plate.
Hold PMT at angle it will be used in microscope (depending on red or green channel) overnight, and check again that oil coverage between the condenser lens and PMT window is intact. There should be no obvious bubbles or inhomogeneities when looking at the photocathode through the condenser lens.
UV cement method
Note: applying UV light to cure UV cement will not harm the PMT photocathode. There have been problems when using UV cement with thick layers of cement (few hundred micron), resulting in permanent bubbles present between the lens and PMT, but the strategy below should not have such problems. It is currently untested, however.
A relatively foolproof way to do the PMT condenser lens bonding with UV cement would be to fill the gap between the condenser lens (flat, optical surface) and the PMT window with another piece of glass (index of refraction ~1.5), and then only use thin UV cement layers, like when bonding a doublet lens, between all the glass pieces. Pieces of coverglass would work fine for this. It would just be necessary to find the right thickness of the gap-filling glass, such that there aren't any air gaps, and the condenser lens doesn't have to rise up much beyond its normal seating position (shoulder touching the PMT housing). Two to three #1.5 coverglass pieces ought to do it. After assembling everything dry to test the thickness and fit of the filler, the filler pieces could be cemented to the condenser lens first, and then whole assembly would be cemented to the PMT.
7 Comments
Natalia Orlova
Hi, which oil should be used to couple the PMT to the condenser lens? -N
Daniel Flickinger
A microscope immersion oil, for high index, optical clarity, and stability. I'm not sure what exactly we used, unfortunately. Whatever we found laying around...
Rob Campbell
Can I clarify some of the steps above before proceeding?
With 5 minute Epoxy we are sealing part J003121 to the PMT so that the oil can leak into the gap between the part and the PMT? So after this step, the PMT and J003121 are linked together? If so, I don't understand what you mean by "Add PMTMountPlate before Kwik-Sil sets" or about the "mount plate being pushed down". Isn't J003121 the mount plate?
As I read the instructions, the idea seems to be to place the lens on the oil, mop up the excess and check for bubbles. Then remove the lens, apply glue, and re-seat the lens so that the glue is between the lens and J003121. Is that correct? Aren't there still issues with bubbles during the re-seating?
Daniel Flickinger
Hi Rob. I clarified the procedure. The first step is just to seal around the PMT window where there is a crack between it and the PMT body–you don't use the 5-min epoxy to attach the PMT to anything. Also, you don't remove the lens after putting it on the first time. Basic procedure: seal around PMT window (epoxy), add oil, add lens, check for bubbles and clean up excess oil, add qwik-sil to PMT body around lens (or on mating surface of J003121–either way), quickly add J003121 (PMTMountPlate) while holding lens down, screw down J003121, wait a little, check for leaks. If there are leaks between the lens and J003121 (about half the time when I've done this), then this crack can be sealed with epoxy. I've never seen leaks between the PMT body and J003121.
Rob Campbell
Thanks. But I think I still don't understand something: what am I adding the oil to? The "add J003121" step is after the oil and lens step and I thought the procedure was:
1) Seal PMT window
2) Screw J003121 to PMT
3) Apply oil onto PMT window
4) Place lens into J003121 and check for air bubbles
5) Mop up excess oil and seal lens with Qwik-Sil
Whilst that seems not be what you're describing (with my steps there can be no Qwik-Sil between the mount plate and the PMT, which you describe), I don't understand what you're getting at. e.g. If the mount plate is not yet coupled, to what do you add the oil and where do you place the lens?
Daniel Flickinger
Hmm...I'm not quite sure where you're confused. You put the oil on the PMT after sealing around the window. There is a well around the window where the oil goes–the window is recessed--not flush with the outer surface. The lens also has a feature machined into it that fits into the well, so it can be added and located relatively precisely without J003121 being used at all. Not having J003121 present when you're first adding the lens will probably make it a little easier to put the lens on at an angle, which will help you to avoid getting a large bubble. Take a look at the PMT and lens once again, and see how they fit together dry to understand the original procedure. Hmm...I can see some advantages and disadvantages to the alternate procedure of putting J003121 on before the lens, but I think the disadvantages outweigh the advantages slightly. If you want to explore different procedures, we should talk on the phone or something, to avoid tons of typing.
Rob Campbell
Ahhh.... I understand now. Thanks.