View from... SPIE optics and photonics 2009: Soft-X-ray lasers' calling

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VIEW FROM SPIE OPTICS AND PHOTONICS 2009

Soft-X-ray lasers calling

High-resolution microscopy, lithography and materials analysis all look set to benet from the emergence of compact and efficient table-top soft-X-ray lasers.

Rachel Won

The latest progress being made in so-X-ray lasers which emit light in the wavelength range

250 nm certainly attracted much attention at this years SPIE Optics and Photonics conference in San Diego.

Giving a plenary talk on the topic,Jorge Rocca from Colorado State University, USA, explained that research on laboratory X-ray lasers has been ongoing for the past 25 years, with steady progress being made. The goal is the realization ofa convenient source of intense, coherent, so-X-ray beams for scientic and technological applications. The good news is that in recent years, stable, compact, high-repetition-rate sources have startedto be used in small university departments and research laboratories. Emitting coherent radiation with wavelengths that are ten to several hundred times shorter than visible light, these lasers are oen referred to as operating in the extreme UV region of the spectrum.

Thanks to the unique propertiesthey possess short wavelength, high coherence and high photon energy such sources are expected to nd new applications in microscopy, lithography, diagnostics and materials analysis, among other uses.

The shorter wavelength allows improved spatial resolution in both imaging and focusing, where feature size at the 50 nm scale approaching the wavelength of the probe beam can be attained, explained Jim Dunn from the Lawrence Livermore National Laboratory, USA, who was also one of the chairs of the So-X-ray lasers and applications VIII conference session at SPIE San Diego.

A tantalizing prospect is the realization of a high-magnication, high-resolution microscope that operates at a wavelength of 4.5 nm, which is within the water window of carbon and oxygen, that is, between the K-edges, outside which there is a sudden increase in attenuation owing to the photoelectric absorption of photons. Such a microscope could havea signicant impact on biological cell imaging, and this is not far from being a

reality. As reported in Nature Photonics in 2007 (Nature Photon. 1, 336342; 2007), the harmonics from the 13-nm FLASH free-electron laser in Hamburg, Germany, have already reached 2.75 nm (well within the water window), and imaging results are expected soon.