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Xradia manufactures and sells a line of Fresnel zone plate lenses. These zone plates are the highest resolution focusing optics for electromagnetic radiation available. Our zone plates enable imaging resolution better than 30nm. Zone plates have a wide area of application in X-ray science ranging from high-resolution imaging to trace fluorescence mapping at high resolution at synchrotron X-ray sources.
Zone plates are diffractive focusing elements. They work like a grating and use constructive interference of light rays from adjacent zones to form a focus (see figure). The focal length f of a zone plate is a function of its diameter OD, its outermost zone width △Rn and the X-ray wavelength λ:
f = OD△Rn / λ
The resolution of a zone plate is limited to 1.22 △Rn (Rayleigh criterion) requiring narrow zones for the best performance. Xradia zone plates have zone widths smaller than 30 nm for high-resolution applications.
To achieve the best focusing efficiency for hard X-rays, we use gold for the zone construction material. A special manufacturing process has been developed to fabricate high aspect ratio gold structures on freestanding silicon nitride membranes.
With the proper choice of gold zone thickness, high-resolution and high efficiency we make zone plates covering the X-ray energy range from 0.2 - 60 keV (figure below).