High Resolution Without Particle Accelerator

For the first time, physicists perform optical coherence tomography with XUV radiation in the laboratory scale

At the ophthalmologist, it is almost a standard program: optical coherence tomography. With this imaging method, the various layers of the retina can be penetrated by infrared radiation and can be examined more precisely three-dimensionally without the eye having to be touched at all. Medicines can detect diseases like the Green Star without any intervention.

However, this method would have far greater potential for the natural sciences if the wavelength of the radiation used could be shortened and thus a higher resolution of the image could be obtained. Physicists of the Friedrich Schiller University of Jena has just succeeded. They report on their research results in the current issue of the specialist magazine "Optica" (DOI: 10.1364 / OPTICA.4.000903).

First XUV coherence tomography at the laboratory scale

The Jena physicists used extreme ultraviolet radiation (XUV), which was generated in the laboratory for the first time, and thus carried out the first XUV coherence tomography in the laboratory scale. The wavelength of this radiation is about 20 to 40 nanometers - from there it is only a small step up to the x-ray range. " In order to produce XUV radiation, large-scale devices, ie particle accelerators such as the German Electron Synchrotron in Hamburg, are normally necessary, " explains Silvio Fuchs from the Institute for Optics and Quantum Electronics at the University of Jena. " Consequently, an investigation method of this kind would be very expensive, expensive and available only to a few researchers. "

For this purpose, the researchers at the University of Jena focused an ultra-sharp, very intensive infrared laser into a noble gas such as argon or neon. " An ionization process accelerates the electrons in the gas, " says Fuchs. " They emit XUV radiation. " This method is very inefficient, since only about one-millionth of the laser radiation is actually converted from the infrared to the ultra-ultraviolet range, but this loss can be compensated by the use of very strong laser sources. " The bill is simple, the more we enter, the more we get out, " says the Jena expert.

Strong image contrasts arise

The advantage of XUV coherence tomography is, besides the very high resolution, that the radiation interacts strongly with the sample, because different substances react differently to the light. Some absorb more and others less. Thus strong contrasts of contrasts arise, which provide the researchers with important information about the material composition of the object to be examined. " We have produced three-dimensional images of silicon chips, for example, which can be used to make a difference between the carrier material and other materials, " explains Silvio Fuchs. " If this method is also used in biology - for example, in the investigation of cells, which is one of our aims - Then the previous staining of the samples, as is customary in other high-resolution microscopy methods, would not be necessary there. Elements like carbon, oxygen and nitrogen would provide the contrast . "

Until then, the physicists of the University of Jena still have some work to do. " With our current light source, we are able to produce a depth resolution of up to 24 nanometers, which is sufficient to represent small structures, for example in semiconductors, but the structural sizes of current chips are already under this brand In the future it will be possible to achieve up to three nanometers of depth resolution using the method, "says Fuchs. " Basically we have shown that this method can be used in laboratory scale ." A long-term goal could ultimately be to develop a cost-effective and user-friendly device.