Optical coupling grease

[Jon Rosenstiel]

Hey guys, take a look at this stuff, may work ok for plastic scintillator/PMT coupling.

http://www.ofna.com/new/oil.html

I bought a small bottle of the 50000 WT silicone oil, (part #10237 for $9.95). It is quite viscous and quite clear also. I have no idea of it's light transmission qualities. Possibly some of the lists more learned members can pass jugement on that.

Jon Rosenstiel

[guest]

If the fluid is water clear, it will probably work as long as you can contain the stuff in the interface region. I was originally going to use Dow Corning DC200 100,000 CPS silicone fluid for index matching, and silicone glued and taped a strip of 0.01" thick mylar sheet around the business end of a 3" PMT to act as a dam, with the edge sticking up about 1/8" above the photocathode surface. If you are careful in applying the glue, it provides a seal all around the circumfrence of the strip. I was planning to put a bead of silicone glue around the periphery of one end of my plastic scintilator, and then after placing a couple of drops of fluid on the photcathode, carefully inserting the scintiilator so that the glue seals the silicone fluid in place, hopefully avoiding air bubbles in the process. What a pain...
I now have some Dow Corning Sylgard 184 2-part silicone resin, which will act both as glue and index matching agent.
When I have time to dig up the URL again, I will post about a company that has revived the original single-lens hand held microscope. As an accessory the sell a silicone gel used to make long lasting living specimen slides. The gel apparently is used to seal the cover slip in place and allows some oxygen diffusion to the little imprisoned microbes. Anyway, as a gel, the stuff should be more tractable than silicone fluid. In an earlier post, I have also mentioned the possibility of using fiber optic matching gel, and a couple of URLs where it can be found.

[DaveC]

I am reasonably certain that you could also use a thin film of ordinary silicone grease for a good index match. The optical absorption characteristics of the silicone are not very much different from the scintillator plastic.

Dave Cooper

[guest]

Ordinary vacuum grease will probably work better than nothing at all if you absolutely can't find anything else, as the scintillator-to-air-to-PMT interface will give you about 10% reflection loss, but it's better in the long run to find something that isn't cloudy. The microscope folks sell their silicone gal for about 12.95 for a 1oz jar, and that will treat a lot of PMTs.

[guest]

The place that sells the silicone gel for use with microscope slides is www.pocketscope.com. They have online ordering, and I just placed an order for some. We'll see how it looks....Since I'm going to be building a fair spread of detectors using PMTs, I have no objection to trying out a few alternate methods for index matching, as long as the're not too messy.

[Tom Dressel]

Richard:

I am about to spring for a scintillator for my PMT based neutron detector, so by all means keep us informed as to how the PocketPond Gel works!

Tom Dressel

[guest]

I just received 1oz of silicone gel from Pocketscope.com. The stuff is water clear ( I had to look twice to make sure something was in the container) and a real gel instead of a viscous liquid. It looks like it would be just dandy for scintillator -PMT coupling. The price is right. too.