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25 femtoseconds is far less time than the proverbial blink of an eye, yet researchers in the US and Sweden have managed to grab an X-ray snapshot of a micrometre-sized stick figure in that time. Janos Hajdu's team at Uppsala University, Henry Chapman and colleagues at the University of California, Livermore and their associates at the University of California, Davis, Stanford Synchrotron Radiation Laboratory, Spiller X-ray Optics, Livermore, and Technical University of Berlin, report in the December issue of Nature Physics how an image, patterned on to a metal film, was snapped a trillion times faster than a conventional flash photograph, just an unimaginably short moment before it evaporated at a temperature of 60,000 Celsius. The team exploited the free-electron FLASH laser at DESY, Deutsches Elektronen Synchrotron facility in Berlin to demonstrate an important proof-of-principle for a technique that should enable atomic-scale imaging of the structure of a much wider range of molecules than is possible using conventional synchrotron sources. Theory suggests that a single diffraction pattern could be recorded from a large macromolecule, a virus, or even a cell if a suitably short and bright X-ray pulse is aimed at the sample. Only one diffraction pattern is possible because the sample would be fried by this pulse, so to speak. However, such data could be invaluable in studying macromolecular proteins, for instance without the need to crystallize them. Chapman and his colleagues believe that free-electron lasers represent an exciting development that could have wide impact in research from structural biology to nanotechnology. Such a laser produces an intense and extremely short burst of X-rays, which allows information about individual organic molecules to be assimilated, without the researcher first having to obtain X-ray quality crystals of their target substance. One question that remained open was whether or not that single diffraction pattern, recorded under such extreme conditions, could subsequently be reconstructed to produce undamaged sample information. Chapman and his colleagues have demonstrated that it can. "These results could become a standardized method," Chapman explains, "This imaging could be applied at the cellular, sub-cellular and down on to single molecule scale." There is some way to go before this is possible and Chapman and his colleagues have so far demonstrated resolution way below the atomic in the present study. However, they suggest that once the first new generation free-electron sources, such as the Linac Coherent Light Source (LCLS) at the Stanford Linear Accelerator Center in the US, come online atomic-scale resolution will then be possible. Related links:
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Stick man snapshot  The 25 femtosecond diffraction |
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