Exact zone plate design and its applications in the extreme ultraviolet region

Zone plates, as critical components for achieving high-resolution characterization, are widely used in nanoprobe technology and microscopic imaging systems based on synchrotron radiation. However, in the extreme ultraviolet (EUV) region, the diffraction efficiency of high-resolution Fresnel zone plates (FZPs) is much lower than the theoretical diffraction efficiency, which affects the imaging efficiency and quality. To reveal the reasons for low diffraction efficiency, we investigate the influence of the approximation design. The traditional structure based on the paraxial approximation ignores the high-order small quantities of the product of the imaging wavelength and the number of zones. As the zone number increases, this approximation in the EUV region no longer holds. On this basis, we propose an exact design of the zone plate from Fermat’s principle to improve its diffraction efficiency, which is validated by numerical calculations.