Science
In reply to the discussion: Quantum Entanglement, Dark Counts, Coincidence Detection [View all]mindwalker_i
(4,407 posts)They do sell a type-II BBO, and it says there's a 5 degree separation I think from the pump, which sounds about right. So the cones come off at 5 degrees, but if the crystal is tilted, it will change that angle depending on which way it's tilted, correct? So at some point the cones just touch along that one line, and all the entangled photons are there. Which way should the tilt happen? Rotating it around the beam doesn't sound like it, so is it, say, moving that major optical axis closer to the beam in back and further away in the front? That seems like it would be reasonable.
Newlight's NCBBO5300-405(II)-HA5 is 3mm thick, 5mm x 5mm in the other two dimensions, cut for type II phase matched SPDC pumped by 405nm, with a half opening of 5 degrees. Mounted in a 1" holder. I could scan the two cones to a detector to get the positions of the cones, then keep doing that while rotating the crystal slowly. In contrast, the paired BBO crystals are .5mm thick. Would the type II work, rotating, reflecting out the pump and such, giving off more entangled pairs?
Unfortunately, I haven't found terribly good info on the net for showing how these work or estimating the brightness.