Scientists have successfully generated the world's sharpest X-ray beam which is ten thousand times thinner than a strand of hair.
This fine beam of X-ray light barely 5 nanometres in diameter, created by researchers led by Professor Tim Salditt from the University of Gottingen, allows focusing on smallest details.
"Instead of a common lens, we use a so-called Fresnel lens which consists of several layers," said co-author Dr Markus Osterhoff.
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.
"This slice has 50 to 60 silicon and tungsten layers, comparable to growth rings of a tree," said team member Florian Doring.
"And the layer thicknesses have to be extremely precise," Christian Eberl added.
The wire slice with a size of only about two thousandth 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.
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.
Until recently it was even debated whether fundamental limits of X-ray optics would stand against such small focal widths.
The outstanding brilliance of he Deutsches Elektronen-Synchrotron (DESY)'s X-ray light source PETRA III helped to make a usable nano focus possible.
The fine X-ray beam opens up new possibilities for materials science, eg the investigation of nano wires to be used in solar cells.
"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 nanometres," said DESY researcher Dr