Virtual lens improves X-ray microscopy
X-rays provide unique insights into the interior of materials, tissues and cells. Researchers at the Paul Scherrer Institute PSI have developed a new method thanks to which X-ray images of materials are even better: The resolution is higher and allows more precise conclusions about material properties.
To do this, the researchers moved an optical lens and recorded a number of individual images, from which they calculated the actual image with the help of computer algorithms. This is the first time that they have applied the principle of Fourier ptychography to measurements with X-ray light. The results of their work at the Swiss Synchrotron Light Source SLS have been published in the journal Science Advances.
Using X-ray microscopes, researchers at the PSI in computer chips, catalysts, bone fragments or brain tissue. The short wavelength of the X-ray light makes details visible that are a million times smaller than a grain of sand - i.e. structures in the nanometer range (millionths of a millimeter). As with a normal microscope, the light hits the sample and is deflected by it. A lens collects this scattered light and produces a magnified image on the camera. However, tiny structures scatter the light at very large angles. If you want to resolve them in the image, you need a correspondingly large lens. "But it is extremely difficult to produce such large lenses," says Klaus Wakonig, a physicist at PSI: "In the visible range, there are lenses that can capture very large scattering angles. In the X-ray range, however, this is more complicated because of the weak interaction with the lens material. As a result, usually only very small angles can be captured or the lenses are very inefficient."
The new method developed by Wakonig and his colleagues gets around this problem. "The result is as if we had measured with a large lens," the researcher explains. The PSI team uses a small but efficient lens, such as those commonly used in the X-ray microscopy is inserted and shifts it over an area that an ideal lens would cover. Thus, a large lens is created virtually. "In practice, we take the lens to different points and take an image at each," Wakonig explains. "Then we use computer algorithms to combine all the images to create a high-resolution image."
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