I've actually done this. A piece of DBEF between two retarders more or less does what we need. However, the error in most wave sheets means that the polarization state of both the reflected and transmitted light is not very 'clean' after passing through two retarders. If you take two pieces of retarder and place them between two linear polarizers in an orientation that extinguishes the light, then the extinction is never as good a only two crossed polarizers- same issue.
Ideally, we'd find the material in question that performs the desired operation in one step. I'm looking for the stuff after seeing the material referenced in a patent. The guy said Merck made it, I've tried evry possible way to get in touch with someone knowledgable at Merck with no luck...
thanks again.