Resolution-enhanced approaches in digital holography

Resolution is an important issue in inspection of objects on microscopic scale. Various approaches have been investigated to increase the optical resolution behind the diffraction limit of an optical imaging system. However every time the optical resolution of a fixed optical system is overcome it is possible to speak of super-resolution. Demonstration that super-resolution have been deeply investigated in interference microscopy through various approaches. Here we discuss briefly the different techniques that have been adopted in interferometry and specifically in digital holography (DH). Then we illustrate a novel method that uses a dynamic diffraction phase-grating for increasing synthetically the aperture of a DH imaging system in lens-less configuration. Consequently the optical resolution of the DH systems can be increased of a factor of 3. The aim of the study is to demonstrate that super-resolution is possible and is a practical and viable method for a coherent optical microscope. We take benefit of the numerical reconstruction properties of DH in combination with diffraction grating to get super-resolution. The approaches could be used for metrology and imaging application in various fields of engineering and biology.