Sandwich hologram interferometry: a new dimension in holographic comparison.

New methods are introduced that utilize interferometric comparison of images of diffusely reflecting objects from different hologram plates that are sandwiched together. To make the plate positions optically and mechanically identical during reconstruction and exposure, they are also exposed in sandwiches. If the two sandwiched hologram plates are separated by a small distance a new method of fringe evaluation can be used. Fringes caused by object tilt between two exposures can be eliminated by an analogous, but much larger, tilt of the sandwich hologram during reconstruction. Even the direction of tilt, forward or backward, is found this way.