I'm not sure what you mean by "conformal mirror" Do you mean "conformal' as in an angle-preserving mapping of one surface to another in the complex plane ? I'm afraid I couldn't find any mention of a conformal mirror in the holographic literature.dcgman wrote:I've noticed this effect when processing the recording of a purely conformal mirror- where's the surface relief there?
At any rate, if the mirror is holographically recorded, the pertinent beams will record an interference set. As Ed Wesley has pointed out, the recording beams give rise to subsidiary beams due to spurious reflections within the emulsion, which also record, so there are multiple recordings, albeit the spurious recordings are relatively weak. However, I assume that the emulsion thickness gives you Bragg diffraction as the end product, which is lambda-selective as well as angle-selective. That is, Q>10. However, if the emulsion thickness were reduced for the same recording geometry, there will be some point at which Q<<10. At this point, you get into the Raman Nath regime and the diffraction will be lambda-independant. All wavelengths will diffract. Also, as the emulsion gets thinner, the spurious recordings mentioned above will stand out more, as most of the spurious recordings are in recorded in transmission geometry. Initially, however, before the Bragg planes have begun to amplify from the latent image, surface distortions will cause Raman Nath diffraction resulting in the rainbow observed at the early stages of development. It's also possible that the spurious beams, recorded in a transmission geometry, will predominate at the early stages of development.
Jeff Weil has mentioned holding up the plate in the light in transmission reconstruction.
Another idea might be to reconstruct the hologram with a single, unexpanded laser beam (in a non-actinic wavelength for the emulsion, of course!). If you see multiple orders, then you probably have a low frequency surface relief grating.Jeffrey Weil wrote:While the plate is wet and you see the reflected dim rainbow image hold the plate up to the light and see if there is a bright transmission image, in transmission mode. That might help the dcg pros here figure it out.