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EUV holography makes x-ray lenses

10 Dec 2004

Swiss researchers demonstrate a convenient way to mass produce high-resolution x-ray optics.

Holography with extreme ultraviolet (EUV) light could be the answer for rapid, mass production of high-performance lenses for the x-ray region, according to Swiss scientists (Applied Physics Letters 85 2700).

Emerging techniques such as x-ray microscopy and advanced lithography are placing continual demands on the imaging resolution of x-ray optics. To date, the best lenses are electron-beam written Fresnel Zone Plates (FZPs) which offer an imaging resolution on the order of 20 nm. However, researchers would like to improve on this so that they can perform better imaging of magnetic domains and cell structures, for example.

FZP lenses consist of a series of concentric "phase-shifting" rings known as zones that are formed on a transparent substrate. The imaging resolution of a FZP is related to the width of the smallest zone.

"The resolution is limited by the difficulty of making the diffraction optics with a very high degree of perfection," Harun Solak, a researcher at the Paul Scherrer Institute in Switzerland, explained to Optics.org. "The novel holographic method that we have reported should answer the main challenges in the production of such lenses."

Solak and his colleagues have now made high performance FZPs using holography at 13 nm for the first time. As x-ray microscopy grows in popularity, their technique could be ideal for mass production as it requires a fabrication time of seconds instead of the hours required by electron beam writing.

The Swiss team transmit 13 nm light through a mask containing two FZPs and generate an interference pattern on a layer of photoresist. The result is a new "daughter" FZP with a structure twice as fine and thus double the imaging resolution of its two parent FZPs. They have tested the method with two parent zone plates with a minimum zone width of 120 nm and created a daughter FZP with a width of just 60 nm.

"This development is important since it provides a way to make x-ray lenses with potential to push the resolution in x-ray microscopy to below 10 nm," said Solak.

Oliver Graydon is editor of Optics.org and Opto & Laser Europe magazine.

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