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EN
Information about certain physical states of an examined object is encoded in the distribution of the fringe contrast in the metrological interference images of the object. Determining the contrast is one of the steps of converting the image into the distribution of the measured quantity in holographic fringe-contrast interferometry. In this paper, three methods of determining the fringe contrast in interference images containing speckle noise are compared. As the criterion for comparing the methods, the mean absolute error has been used. It turns out, in accordance with this criterium, the most effective method is the phase-shifting one.
EN
Diffraction microtomography in coherent light is foreseen as a promising technique to image transparent living samples in three dimensions without staining. Contrary to conventional microscopy with incoherent light, which gives morphological information only, diffraction microtomography makes it possible to obtain the complex optical refractive index of the observed sample by mapping a three-dimensional support in the spatial frequency domain. The technique can be implemented in two configurations, namely, by varying the sample illumination with a fixed sample or by rotating the sample using a fixed illumination. In the literature, only the former method was described in detail. In this report, we precisely derive the three-dimensional frequency support that can be mapped by the sample rotation configuration. We found that, within the first-order Born approximation, the volume of the frequency domain that can be mapped exhibits a missing part, the shape of which resembles that of an apple core. The projection of the diffracted waves in the frequency space onto the set of sphere caps covered by the sample rotation does not allow for a complete mapping of the frequency along the axis of rotation due to the finite radius of the sphere caps. We present simulations of the effects of this missing information on the reconstruction of ideal objects.
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