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In recent years laser-plasma based accelerators have provided access to GeV electron energies within laboratory scale facilities. This has opened many new research avenues, one of which focuses on the application of the ultrafast (few femtoseconds) X-ray source that is generated by the electron oscillations. A key strength of the X-ray source is its smooth broadband nature which makes it perfect for X-ray absorption spectroscopy; these measurements provide a wealth of information about the structure and state of a sample. XANES (X-ray Absorption Near Edge Structure) and EXAFS (Extended X-ray Absorption Fine Structure) in particular, provide a simultaneous measurement of the temperature and structure of both the electronic and ionic distributions. These techniques have been used with great success over the last few decades at synchrotron facilities worldwide, however, these large-scale facilities are relatively costly to construct, and beamtime slots are highly competitive and generally have a short timeframe.
We present high-resolution single-shot K-edge XANES and EXAFS measurements of copper samples from recent experiments using a laser-wakefield accelerator at the laboratory-scale Gemini laser facility (building upon results of [1]). Up to 106 photons/eV per shot at 9 keV were measured. We demonstrate that this source is capable of single-shot simultaneous measurements of both the electron and ion distributions in matter heated to eV temperatures. The unique combination of a high-flux, large bandwidth, few femtosecond duration x-ray pulse synchronised to a high-power laser will enable key advances in the study of ultrafast energetic processes such as electron-ion equilibration and non-thermal phase transitions. Additionally, the development of this laser-plasma accelerator X-ray source will enable high quality laboratory scale XAS facilities to be realised.
References
[1] B. Kettle et al. “Single-shot multi-keV X-ray absorption spectroscopy using an ultrashort laser-wakefield accelerator source”, Phys. Rev. Lett. 123, 254801, (2019).
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