Poisson's Spot at New Shapes of Damage of a Circular Disk

D. Dimića, D. Arsenovićb aFaculty of Natural Sciences and Mathematics, University of Niš, Niš, Serbia bInstitute of Physics, University of Belgrade, Belgrade, Serbia

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Poisson's spot is the bright point in the centre of the geometrical shadow of a circular object, as a consequence of Fresnel's diffraction. In the literature, the relative intensity of Poisson's spot has been examined in the case of small deviations from the circular cross-section of the circular diffraction obstacle, simulating a surface roughness. It was shown that small amounts of surface roughness can completely remove Poisson's spot. In this paper, a specially adapted analytical-numerical method is presented to study this phenomenon. With this method, the influence of larger deviations from the circularity of a diffraction obstacle on Fresnel diffraction can be examined. The deviations from the ideal cross-section of a lightened circular object are of the semi-circular shape. The effect of different modifications to the cross-section of this type was analyzed. All of the simulated diffraction images are similar to the case of a circular cross-section, showing Poisson's spot. However, the obtained theoretical results show that the relative intensity of Poisson's spot falls oscillatorily as the size of deviations increases. The oscillatory dependence is explained by using the concept of Fresnel zones. The method can be used for modeling future diffraction experiments of both electro-magnetic and matter waves.

DOI:10.12693/APhysPolA.138.345 topics: interferometry, Poisson's spot, Fresnel zone