Single-Shot Multi-keV X-Ray Absorption Spectroscopy Using an Ultrashort Laser-Wakefield Accelerator Source

Abstract

Single-shot absorption measurements have been performed using the multi-keV x rays generated by a laser-wakefield accelerator. A 200 TW laser was used to drive a laser-wakefield accelerator in a mode which produced broadband electron beams with a maximum energy above 1 GeV and a broad divergence of $\ensuremath{\approx}15\text{ }\text{ }\mathrm{mrad}$ FWHM. Betatron oscillations of these electrons generated $1.2\ifmmode\pm\else\textpm\fi{}0.2\ifmmode\times\else\texttimes\fi{}{10}^{6}\text{ }\text{ }\mathrm{photons}/\mathrm{eV}$ in the 5 keV region, with a signal-to-noise ratio of approximately $300\ensuremath{\mathbin:}1$. This was sufficient to allow high-resolution x-ray absorption near-edge structure measurements at the $K$ edge of a titanium sample in a single shot. 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 by comparison with density functional theory simulations. The unique combination of a high-flux, large bandwidth, few femtosecond duration x-ray pulse synchronized to a high-power laser will enable key advances in the study of ultrafast energetic processes such as electron-ion equilibration.