Estimation of objects transverse parameters in off-axis and inline Fresnel digital holography

摘要

In this report transverse parameters of objects registered with inline and off-axis Fresnel digital holography schemes were estimated: maximum transverse dimensions of objects, size and quantity of object resolution elements. By determining allowed locations of diffraction orders under reconstruction, new expressions for estimation of objects transverse parameters were obtained. In case of off-axis holography it is desirable that object should not overlap with zero-order and twin images. If object and twin images are located on opposite sides relative to zero-order under reconstruction, this is case of preventing of cyclic shift of twin image (PCS). If twin image is located on both sides relative to zero-order under reconstruction but don't overlap with object image, this is case of assumption of cyclic shift of twin image (ACS). ACS case allows to register digital holograms of larger objects compared to PCS case. However, for example, for automatic image processing, separate display of object and twin images relative to zero-order is often required. It was found that ACS case allows to register holograms with distance between the object and hologram 1.5 times lesser than in PCS case. And maximum transverse dimension of object in ACS case is always greater than in PCS case by the half of hologram size. For verification of obtained estimates, off-axis digital Fresnel holograms with 2048x2048 pixels were optically registered. Contour images located behind static scatter were used as objects. Confirmations on transverse object parameters estimates, satisfying ACS and PCS cases, were derived. These results demonstrate correctness of obtained quantitative estimates.