Digital Holographic Imaging Based on Shearing Interferometry

Abstract

In-line and off-axis digital holography are now used in a wide range of domains such as fluid mechanics [1,2] and microscopy imaging [3-6]. In the basic in-line holographic configuration (no phase shifting, no sequential recording), the reference and object waves are parallel and the path lengths of both waves are equal. For this reason, the in-line holography is only able to provide an amplitude image of the object. Therefore, it can not be used to measure the phase contrast of any transparent object. For a multiple object recovering, such as particles [1], this method suffers from the presence of the intrinsic speckle noise generated by the twin images during the reconstruction. In the off-axis holography (single-shot recording), the reference wave is shaped to provide a spatial separation in the reconstruction plane or in the Fourier plane of the hologram. In this case, the virtual and real images are well spatially separated during the reconstruction. The use of an independent reference wave induces a sensibility to external perturbations such as vibrations, temperature changes, etc., and leads to an increase in the setup complexity. So as to simplify the setup and to get a real immunity to external perturbations, the in-line configuration is well adapted, but the faculty for the phase contrast recovering has to be invented. In order to overcome both the problems related to the reference wave in off-axis holography and the impossibility of measuring the phase contrast in in-line holography, we propose in this paper a new technique having new features in digital holography: i) simplify the recording set-up by eliminating the reference wave and ii) measure of the phase contrast of the object. This new approach in digital holography is based on the use of a spatial phase modulation so as to produce multiple replicas of the incoming diffracted wave at a given distance.