Optical matching gel
Posted: Sun Oct 14, 2012 1:44 amAnyone know where I can get some of this stuff somewhere cheaper than an arm and a leg? I need some for my PMT/Scintillator.
What indices of refraction are you trying to match? Since most things are very approximately 1.45, there are a lot of things that work well, actually. Low-creep silicone grease, crazy glue (sometimes fractures)...one of the common plastics in a solution - it all works better than an air gap. Most of the pro stuff I've taken apart uses the grease, but I've tried a lot of things that seemed fine, depending on the mechanicals of the situation. Heck, even a very thin layer of plain old paraffin works or old airplane glue the (kind they no longer sell). But it all depends some on what you're trying to match to what. You want to hit the geometric mean of the two IR's if you can. I've got some of that 'arm and a leg" stuff too - two component, like epoxy. It's ok but not worth the differential in price IMO, and like anything that gets hard, can fracture and suddenly change your sensitivity without any warning.
Some things you can't really match and have to live with it. ZnS:Ag is in the 4's for IR and nothing matches that (that you can get).
Bottom line - if it's clear and has some give, it's going to be tons better than an air gap - after that, you're fighting for the last couple dB, and it might not be worth it to go to extremes, as that can be made up in gain someplace else.
I can send you some junk I use if you like if it hasn't gotten hard or something.