Interferometric sinograms of transparent objects with stepping wise shifted Ronchi ruling for optical tomography

Abstract

An experimental set-up to achieve tomographic images of slices belonging to transparent objects is presented. The proposed system is based on an interferometer which employs two windows in the object plane and a translating absorptive grating (Ronchi ruling) in the frequency plane. In the image plane, replicated windows can be brought to superposition by proper adjustment of the windows' spacing and the grating period. After adaptation of this interferometer to tomographic measurements, the phase of the projections result encoded as interference fringes, thereby forming a composite interference pattern in the plane of the corresponding sinogram (interfero-sinograms). Using phase-stepping techniques, four phase-shifted interfero-sinograms are found after proper translation of the grating. Then wrapped a and unwrapped phase is extracted as a conventional interferogram to obtain a sinogram to be subjected to a filtered backprojection algorithm for reconstruction. As experimental results, the reconstructions of some transparent samples are presented.