Talk:Spontaneous parametric down-conversion

What's the process?
Does anyone have any information on exactly what the process is? What's does the incoming photon interact with in the crystal and how does the matching of the output photons arise? 79.79.253.135 (talk) 01:25, 30 May 2018 (UTC)
 * The article used to state: "The fundamental reason why some of the photons are split is not understood as of 2008. " The author of that book is not a physicist, but the book is apparently well-researched. J-Wiki (talk) 05:00, 30 May 2018 (UTC)

Resonant interaction and Draft:three-wave equation
There is now an article on resonant interaction and I believe that it provides the correct theoretical background for this article. More precisely, Draft:three-wave equation does this too, since assorted non-linear optics papers utter the words "chi-two crystal" and "three-wave resonant interaction" in the same breath. I don't want to modify this article because I don't know the details and cannot readily verify what the deal really is. 67.198.37.16 (talk) 01:51, 17 September 2020 (UTC)


 * Interesting, could be. Unfortunately, I don't know enough about this to judge whether or not it is the right theoretical background. I'll ask some experts. Richard Gill (talk) 09:52, 25 November 2022 (UTC)

Remove portion regarding olive oil and lasers?
I am almost certain the process described here is one of natural chlorophyll fluorescence, rather than true spontaneous parametric down-conversion (https://pubmed.ncbi.nlm.nih.gov/11128149/) as such, I propose we remove this sentence. 50.233.115.50 (talk) 17:58, 25 August 2022 (UTC)


 * The anonymous editor, User:50.233.115.50 removed the portion of the article on olive oil and lasers. Excellent. But he or she also deleted this section of the article’s Talk page. I think it should stay here, so I put it back. We shouldn’t rewrite history to hide the fact there has been discussion about this issue. Richard Gill (talk) 22:57, 10 January 2023 (UTC)

Some improvement of text was necessary
I feel that the text and especially the description of the image of the two intersecting cones was not very clear. Having checked the literature and also consulted with experts, I made some changes, in order to emphasize that some photons emerge in pairs, each moving in a straight line from the source along the surface of one of the two cones, always one polarized horizontally, one vertically. The pairs take paths which are symmetrical arranged, and arranged in such a way that if one photon travels out along one of the lines where the surfaces of the two cones intersect, the other photon travels out on the other such line. Since both |H>|V> and |V>|H> are possible (H standing for horizontal polarization, V for vertical, and the order of the two kets corresponding to "left hand photon", "right hand photon"), and we do not look to see which one is the case, both possibilities exist in quantum superposition. Richard Gill (talk) 09:49, 25 November 2022 (UTC)