Abstract
The central dark spot in the focus of the spiral zone plate can be arbitrarily decreased by an introduction of the π-phase jump around the circle at properly chosen radius. Unfortunately, the closer to the centre is the position of the first maximum, the smaller is its height in comparison with the subsequent maximum. An improvement in this matter can be obtained by dividing the aperture into more annular subapertures with properly chosen values of their radii and transmittances or by other techniques designed for superresolving filters. This new modification of the spiral zone plate is verified experimentally and its applicability to metrological purposes is suggested.
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