Focusing an XUV beam with a beam of atoms used as a lens. Credit: MBI BerlinResearchers from the Max Born…
Focusing an XUV beam with a beam of atoms used as a lens. Credit: MBI Berlin
Researchers from the Max Born Institute (MBI) have developed the first reflection lens that focuses on extreme ultraviolet rays. Instead of using a glass lens, which is invisible in extremely ultraviolet, the researchers have shown a lens formed by an atomic atmosphere. The results, which provide new opportunities for imaging of biological samples in the shortest time frames, were published in Nature .
A tree trunk partially immersed in water seems to be bent. For hundreds of years people have shown that this is caused by fracture, ie the light changes the direction when traveling from one medium (water) to another (air) at an angle. Breaking is also the underlying physical principle behind lenses that play an indispensable role in everyday life: They are part of the human eye, they are used as spectacles, contact lenses, like camera targets and to control laser beams.
The following detection of new regions in the electromagnetic spectrum, such as ultraviolet (UV) and x-ray radiation, developed lens lenses that are specifically adapted to these spectral areas. However, electromagnetic radiation in the ultra-ultraviolet (XUV) area is something special. It occupies the wavelength range between the UV and X-ray atoms, but unlike the two latter radiation types, it can only travel in vacuum or very rare gases. Nowadays XUV rays are often used in semiconductor lithography as well as in basic research to understand and control the structure and dynamics of matter. They enable the generation of the shortest human light pulses with the attosecond’s duration (one attocase is one billionth of one billionth of a second). However, despite the large number of XUV sources and applications, no XUV lenses have existed so far. The reason is that XUV radiation is strongly absorbed by any solid or liquid material and simply can not pass through conventional lenses.
Invisible rainbow generated by a jet of helium atoms. Light with “colors” near helium resonances is deflected either up or down. Credit: MBI Berlin
To focus XUV beams, a team of MBI researchers have taken another approach: They replaced a glass lens with that formed by an atomic atmosphere of a noble gas, helium. This lens benefits from the high transmission of helium in the XUV spectral range and can be controlled at the same time by changing the density of the gas in the beam. This is important to set the focal length and minimize the spot size of the focused XUV rays.
In comparison with curved mirrors that are often used to focus XUV radiation, these gaseous refractive lenses have a number of advantages: A & # 39; new “lens is constantly generated by the atomic flow in the beam, which means that damage problems are avoided. Furthermore, a gas lens results in virtually no loss of XUV radiation compared to a typical mirror.” This is a big improvement, since the generation of XUV rays is complex and often very expensive, “says Dr. Bernd Schuette, MBI researcher and the corresponding author of the publication.
In the work, researchers have also shown that a nuclear beam can act as a prism that breaks the XUV radiation into its constituents spectral components . This can be compared to observation of a rainbow, due to the fact that the sun’s light is broken in its spectral colors with water drops, except that the “colors” of the XUV light are not visible to a human eye.
The evolution of the gas phase lenses and prisms in The XUV region makes it possible to transfer optical techniques that are based on refraction and are commonly used in the visible and infrared a part of the electromagnetic spectrum of the XUV domain. Gas lenses can for example utilized to develop an XUV microscope or to focus XUV beams to nanometer spot sizes. This can be applied in the future, for example, to observe structural changes of biomolecules in the shortest time frames.
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L. Drescher et al., Extreme Ultraviolet Refraction Optics, Nature (2018). DOI: 10,1038 / s41586-018-0737-3