May 16, 2012 |
Graphite enters different states of matter in ultrafast experiment
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(Nanowerk News) For the first time, scientists have seen an X-ray-irradiated mineral go to two different states of matter in about 40 femtoseconds (a femtosecond is one quadrillionth of a second).
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Using the Linac Coherent Light Source (LCLS) X-ray Free-Electron Laser (XFEL) at SLAC National Accelerator Laboratory at Stanford, Stefan Hau-Riege of Lawrence Livermore National Laboratory and colleagues heated graphite to induce a transition from solid to liquid and to warm-dense plasma.
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Ultrafast phase transitions from solid to liquid and plasma states are important in the development of new material-synthesis techniques, in ultrafast imaging, and high-energy density science.
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By using different pulse lengths and calculating different spectra, the team was able to extract the time dependence of plasma parameters, such as electron and ion temperatures and ionization states.
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Demonstration of ultrafast disintegration of matter by 2 keV LCLS pulses: The team combined techniques commonly used in solid state physics (Bragg reflection) with techniques from plasma physics (spectroscopy of diffusely-scattered light) to characterize ultrafast heating in graphite.
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"We found that the heating and disintegration of the ion lattice occurs much faster than anticipated," Hau-Riege said.
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The research provides new insights into the behavior of matter irradiated by intense hard X-rays. Though the study ultimately serves as a breakthrough in plasma physics and ultrafast materials science, it also affects other fields such as single molecule biological imaging and X-ray optics.
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For single-molecule bioimaging, the team found that in certain cases it may be substantially more difficult than anticipated because energy transfer is surprisingly fast. In X-ray optics, they found that the damage threshold is lower than anticipated.
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This is the first XFEL high-energy density science experiment that used inelastic X-ray scattering as a plasma diagnostic.
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The research is scheduled to appear in the May 21 edition Physical Review Letters.
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Other Livermore researchers include Alexander Graf, Tilo Doppner, Rich London, Carsten Formann, Siegfried Glenzer, Matthias Frank and Joe Bradley.
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In addition to SLAC National Accelerator Laboratory, participating institutions include Universitat Duisburg-Essen; Max Planck Advanced Study Group, Center for Free Electron Laser Science; Max Planck Institut fur medizinische Forschung; and Max Planck Institut fur Kernphysik, all of Germany.
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