Coherent imaging by digital holographic microscopy: focusing capabilities and depth of focus in the reconstructed images

Observing at a microscope object having a three-dimensional (3D) complex shape only a portion of it appears in focus since essentially a single image plane is imaged. Up to now only two approaches have been developed to obtain an extended focused image (EFI). An EFI shows all details of the object in focus. Both methods having severe limitations since one requires mechanical scanning while the other needs specially designed optics. We demonstrate that an EFI image of an object can be obtained by means of digital holography (DH) in a microscope configuration overcoming the mentioned limitations. The novelty of the proposed approach lies in the fact that it is possible to build an EFI by exploiting the unique feature of DH in extracting all the information content stored in hologram (phase and amplitude).

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