Modifidied composite high-NA Fresnel zone plates

A modified composite high-NA Fresnel zone plate, which removes the nonparaxial suppression effect on higher-orders of the old version, is proposed for the focusing and imaging of sotf x-rays and extreme ultraviolet (EUV) radiation. Its main properties, such as the equivalent aperture (or pupil) function, the focal spot shape, the diffraction efficiency and the depth of focus, are analytically and numerically investigated. Such a diffractive optical element is also compared with a photon sieve [Kipp et al., Nature 414, 184-188 (2001)] and a modified Fresnel zone plate that produces a sharp Gaussian focal spot [Cao and Jahns, J. Opt. Soc. Am. A20, 1576-1581 (2003)], in terms of their focusing performances.