Scientists generate world's sharpest X-ray beam

Scientists have generated a X-ray beam with a diameter of barely 5 nanometres, which is ten thousand times thinner than a human hair at the X-ray light source PETRA III, at DESY.

According to the research groups of Professor Tim Salditt from the Institute of X-ray Physics and of Professor Hans-Ulrich Krebs from the Institute of Materials Physics of the University of Gottingen, this fine beam of X-ray light allows focusing on smallest details.

Co-author Dr. Markus Osterhoff said that instead of a common lens, they used a so-called Fresnel lens which consists of several layers. The central support is a fine tungsten wire with the thickness of only a thousandth of a millimetre. Around the wire, nanometre-thin silicon and tungsten layers are applied in an alternating way. The physicists then cut a thin slice from the coated wire.

The wire slice with a size of only about two thousandths of a millimetre is used as a lens. However, it does not diffract light like a glass lens but scatters it like an optical grid generating a pattern of bright and dark patches.

In this case, the thickness of the layers is selected in such a way that the bright areas of the diffraction pattern coincide at the same spot. The more precise the lens is fabricated, the sharper becomes the X-ray focus.

With this method, the physicists obtained an X-ray beam of 4.3 nanometres (millionth of a millimetre) diameter in horizontal direction and 4.7 nanometres diameter in vertical direction.

"Usually, when investigating the chemical composition of a sample, the beam size limits the sharpness of the image. Before this experiment, this limit was at about 20 nanometers," DESY researcher Dr. Michael Sprung said.

The study is published in the research journal Optics Express.