Researchers at Universität Kiel and Universität Hamburg, both in Germany, have achieved a sharper focus of soft x-rays from high-power, free-electron sources than from conventional zone-plate optics. The "photon sieve" method uses pinholes that vary in diameter and distribution over the Fresnel zones to obtain a sharper focal spot, together with the suppression of higher-order and finite-size effects.

The researchers used a 632.8-nm HeNe laser to compare the performance of the technique with that of a zone plate with a minimum structure size of 100 µm. The results verified the technique's superior focus. They reported their results in the Nov. 8 issue of Nature. They hope the sieves will provide new opportunities in x-ray microscopy, spectroscopy and lithography.