Experimental demonstration of the longitudinal image shift in digital holography

In digital holography, it is necessary to know the distance of the object from the recording charge-coupled device camera to obtain a correct numerical reconstruction process. The presence of a plane parallel plate along the path of the object beam, such as a beamsplitter cube, often used in interferometers, affects the actual reconstruction distance. This effect, to our knowledge, has never been discussed in the literature despite the fact that it adds a contribution that cannot be ignored in the reconstruction process. We evaluate the effect for a spherical object wavefront as well as in the case of an extended object.