Optical tomography with parallel projection differences and electronic speckle pattern interferometry

In tomography, a set of object projections taken at different observation angles is measured and used for subsequent reconstruction of the object. In this communication, an experimental technique to obtain edge-enhanced tomographic images of transparent objects using Electronic Speckle Pattern Interferometry (ESPI) is presented. The proposed method is based on sequential measurements of subtraction images of adjacent parallel projections (differences). This procedure approximates to the angular derivative of the Radon transform. Differences are encoded in an interference pattern and can be extracted from ESPI patterns. Due to the change in reference in each measurement, the frequency of the fringe interference pattern does not show high variations. As a consequence, the range of inspection results wider than that of a similar method using constant references. At the end, this method gives the angular derivative of the phase slice through the usual tomographic reconstruction procedures. Simulated and experimental results are shown. (C) 2003 Elsevier B.V. All rights reserved.