Twin-image elimination in in-line holography of finite-support complex objects

Reconstruction of in-line holograms suffers from the superposition of two twin images having different foci but identical information content. A simple iterative method of twin-image elimination is presented here. It is based on the fact that, if the object has a finite support and the recording distance is not too small, the out-of-focus field is known on a large part of the reconstruction plane and is only superposed by the in-focus one inside a restricted support. An iterative procedure is developed to recover the out-of-focus wave inside the in-focus image support. Inverse diffraction then gives the reconstructed image. This procedure can be easily automated and works for finite-support real or complex objects, recorded in geometries with a Fresnel number of ~1.