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No abstract

Some properties ofrhe Fresnei diiiraction held produced by a Cantor bars aperiure are investigated by numerical evaluations of the Fresnel integral. It is found that intensity distributions on the optical axis have a periodicity which includes symmetry. when plotted against o ' / ( t ) where U is the length of an object, i is the illumination wavelength and 1 is the distance of an observation point from the object. The period depends on the level of Cantor bars and shows a ninefold increase as the level of the objcct increases by one.Furthermore, as the level of Cantor bars increases. intensity distributions on the optical axis intensity distributions at observation planes perpendicular to the optical axis show a partially self-similar property. In order to quantify this property, a degree ol self-similarity is defined. As the light is propagated in the diKractian field, patterns with low self-similarity in the Fresnel region close to the aperture plane turn gradually to those with high self-similarity and finally approach the Fraunholer diKractian pattern. kcomP iararian! grndua!!y rmm !8C fzr-!L) !he !!$ar-fiC!d rPgion. on !hC n!hPr hand,