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Message: <blockquote data-quote="Kevin Purcell" data-source="post: 1305252" data-attributes="member: 68323">No implication was taken. Though I have noticed myself when consulting a textbook to write something up (not just on WP) that one often unconsciously "nicks" a sentence or two. I try to avoid that, if possible. I think if you read Steve Ingraham's explaination of SP roof prisms (linked in the article) you might see some borrowed ideas but no stolen text (I was quite careful about that!).The current explanation is better than nothing but it still has a lot of hand waving (not even mention of s- and p-polarized interference or the structure of ). But hopefully it will improve over time.It seems the design of most "reflection-type film-substrate retarder" as they're sometimes called The the system will work as a retarder if the refractive indices of the ambient N0, film N1 and substrate N2 are such that N1 <= square root of N0N2 .So my working hypothesis is you arrange the films to preferentially reflect one the polarizations at the lower interface and allow the "leading" polarization through the interface. Then you propagate that through the film reflect it from a outermost interface then propagating through the film again (so being delayed) until it meets back up with the other polarization and now they're both in phase. I suspect there is an extra (non-obvious) trick that requires three layers but I suspect it has something to do with selecting the polarization. When you do this you can get the phase delay to zero at one frequency. By stacking these blocks (and probably optimizing across the whole set of layers) you can get zero phase delay between s- and p- components of the reflected wave (or any arbitrary phase delay you want to compensate for other delays in the system).Is there an emoticon for handwaving? <img src="data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7" class="smilie smilie--sprite smilie--sprite2" alt=";)" title="Wink    ;)" loading="lazy" data-shortname=";)" />Of course as ksbird would say that's an awful lot of trouble to go to when a porro erector will just do it for free. And yes, I agree with him on that. It is.</blockquote>

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