Zone plates with high efficiency in high orders of diffraction described by dynamical theory

The coupled wave theory is applied to calculate the diffraction efficiency of zone plates used in high orders of diffraction. In contradiction to the existing understanding about 30%-50% of the incident intensity can be diffracted by a single high order if the line-to-space ratio of the zone structures is in the range of 0.1-0.5 and the aspect ratios ape larger than 30:1. Highly efficient diffractive transmission x-ray optics with high numerical apertures and resolving power can be developed without manufacturing extremely small zones which are necessary for zone plates used in the first order. (C) 1997 American Institute of Physics.