New X-ray lens – X-ray chromatic lens makes it easier to look into the nanoworld

More focus on high-energy radiation: For the first time, researchers have developed a lens that can also focus X-ray light at different wavelengths. This is made possible by combining two microstructures, which first break up the short wave radiation and then focus it again. Thus a chromatic lens could make X-ray analyzes easier and less dependent on synchrotron systems.

Achromatic lenses have always been standard in optics and photography. It collects light of different wavelengths by itself and thus enables sharp images to be obtained. These lenses usually consist of two materials, the first of which splits a ray of light into its spectral colors. The second material gathers all the components of the package into a small common point.

How do you focus x-ray light?

However, these achromatic lenses do not work with X-rays – they focus the X-rays slightly differently depending on the wavelength. Christian David, senior author from the Paul Scherer Institute (PSI) in Villigen, Switzerland explains.

As a result, high-resolution X-ray analyzes were previously only possible using “monochromatic” X-ray light. All deviated wavelengths are filtered from the X-ray beam until they are largely homogeneous. The problem, however, is that because a lot of the intensity is lost as a result, this only works with powerful X-ray sources such as synchrotrons – which are expensive, bulky, and often fully confined.

Fresnel lens and microturret

The first x-ray photochromic lens now provides treatment. Unlike conventional lenses, they are not based on two materials with different refractive indices, but use specially created microstructures. The so-called Fresnel zone sheet (FZP), a refraction pattern made of nickel in a silicon nitride film created by nanolithography, is responsible for the focus. These Fresnel lenses have long been used for X-rays.

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Device structure, Fresnel zone plate (B) and refractive structure (C) © Kubec et al / Nature Communications, CC by 4.0

However, the second part of the achromatic lens is new and unusual: it consists of an elongated component, a few hundred micrometers high, the shape and structure of which resembles a small tower or rocket rather than a lens. The building has a four-storey parabolic structure surrounded by intersecting microbial columns. This combination of structures ensures that the X-rays are refracted and scattered according to their wavelength.

Sharp image even at irregular wavelengths

The combination of these two microstructures acts like an X-ray chromatic lens and now allows for the first time to produce sharp images even with “dirty” X-rays of different wavelengths. Initial tests in the synchrotron for X-rays at PSI showed how well this works. To do this, the team led by David and first author Adam Kubik placed a “test image” a few micrometers in size in the beam that focuses on the two parts of the lens.

The result: “While our achromatic lenses provide high spatial resolution and strong contrast across a wide energy spectrum, images with only the Fresnel area plate become very blurred even with small deviations of 200 eV from the target energy of 6.2 keV,” According to the team reports. Thus the new achromatic lens proved that it could still focus sharply even at inconsistent wavelengths without having to readjust it.

New possibilities for X-ray analysis

According to Kubik and colleagues, the new achromatic lens opens new possibilities for high-resolution X-ray analyzes in the future, even far from large-scale synchrotron research facilities. “Our colorimetric X-ray lens will allow for X-ray microscopy that industrial companies can run on their own premises,” Kubik says.

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Among other things, you could benefit from this industrial research, microchip development, batteries and materials research. (Nature Communications, 2022; doi: 10.1038/s41467-022-28902-8)

Source: Paul Scherer Institute (PSI)

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