Stigmatic Imaging by Spherical Fresnel Zone Plates

Abstract

Abstract We present a succinct and convenient formulation for the zone radii of a spherical Fresnel zone plate that produces the stigmatic image of an axial object at a specific finite/infinite distance from the zone plate. By ‘image’ we imply the first order or primary image produced by the zone plate. The variation in zone radii for different conjugate positions and for different values of curvature of the spherical zone plate is demonstrated with the help of numerical results. In order to bring forth the significance of this variation for Fresnel zone plates operating at different regions of the electromagnetic spectrum, the variation is shown for one representative wavelength at each of the four regions of the electromagnetic spectrum, namely, the infrared, the visible, the extreme ultraviolet and the soft X-rays.