Creation and diagnosis of a solid-density plasma with an X-ray free-electron laser

Department of Physics, Clarendon Laboratory, University of Oxford, Parks Road, Oxford OX1 3PU, UK.
Nature (Impact Factor: 41.46). 02/2012; 482(7383):59-62. DOI: 10.1038/nature10746
Source: PubMed


Matter with a high energy density (>10(5) joules per cm(3)) is prevalent throughout the Universe, being present in all types of stars and towards the centre of the giant planets; it is also relevant for inertial confinement fusion. Its thermodynamic and transport properties are challenging to measure, requiring the creation of sufficiently long-lived samples at homogeneous temperatures and densities. With the advent of the Linac Coherent Light Source (LCLS) X-ray laser, high-intensity radiation (>10(17) watts per cm(2), previously the domain of optical lasers) can be produced at X-ray wavelengths. The interaction of single atoms with such intense X-rays has recently been investigated. An understanding of the contrasting case of intense X-ray interaction with dense systems is important from a fundamental viewpoint and for applications. Here we report the experimental creation of a solid-density plasma at temperatures in excess of 10(6) kelvin on inertial-confinement timescales using an X-ray free-electron laser. We discuss the pertinent physics of the intense X-ray-matter interactions, and illustrate the importance of electron-ion collisions. Detailed simulations of the interaction process conducted with a radiative-collisional code show good qualitative agreement with the experimental results. We obtain insights into the evolution of the charge state distribution of the system, the electron density and temperature, and the timescales of collisional processes. Our results should inform future high-intensity X-ray experiments involving dense samples, such as X-ray diffractive imaging of biological systems, material science investigations, and the study of matter in extreme conditions.

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    • "The advent of such light sources stimulated rapid advances in many scientific disciplines ranging from atomic physics [6] [7], study of molecules and chemical reactions [8] [9], to clusters [10] [11] and macroscopic objects [12] [13] [14] exposed to intense laser fields. They are actively used for creating and probing plasmas [15] [16], hot dense matter [16] [17] [18] and warm dense matter [19] [20]. Lower fluences of FELs are used to investigate structural changes within solid-state matter [12] [21] [22] [23] [24]. "
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    • "The capability of hard X-ray free-electron lasers (XFELs) to probe matter on the atomic length scale and femtosecond time scale opens a window into broad scientific areas ranging from single shot images of biological structures12, to imaging the dynamics of matter3, to creating matter in extreme conditions4, and observing nonlinear optical effects in the hard X-ray range5. E. g., the availability of these short x-ray pulses of 50 fs and below holds open the possibility for structure determination of single molecules with atomic resolution by outrunning structural damage678, which continues to be the most important limitation in x-ray protein crystallography9. "
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