Single-pulse (100 ps) extended x-ray absorption fine structure capability at the Dynamic Compression Sector

Abstract

Determining real-time changes in the local atomistic order is important for a mechanistic understanding of shock wave induced structural and chemical changes. However, the single event and short duration (nanosecond times) nature of shock experiments pose challenges in obtaining Extended X-ray Absorption Fine Structure (EXAFS) measurements—typically used for monitoring local order changes. Here, we report on a new single pulse (∼100 ps duration) transmission geometry EXAFS capability for use in laser shock-compression experiments at the Dynamic Compression Sector (DCS), Advanced Photon Source. We used a flat plate of highly oriented pyrolytic graphite (HOPG) as the spectrometer element to energy disperse x rays transmitted through the sample. It provided high efficiency with ∼15% of the x rays incident on the HOPG reaching an x-ray area detector with high quantum efficiency. This combination resulted in a good signal-to-noise ratio (∼103), an energy resolution of ∼10 eV at 10 keV, EXAFS spectra covering 100 s of eV, and a good pulse to pulse reproducibility of our single pulse measurements. Ambient EXAFS spectra for Cu and Au are compared to the reference spectra, validating our measurement system. Comparison of single pulse EXAFS results for ambient and laser shocked Ge(100) shows large changes in the local structure of the short lived state of shocked Ge. The current DCS EXAFS capability can be used to perform single pulse measurements in laser shocked materials from ∼9 keV to 13 keV. These EXAFS developments will be available to all users of the DCS.

Towards a dynamic compression facility at the ESRF

“…However, XANES of laser-shocked Fe has also been measured at MEC (Harmand et al, 2015), but with limited data quality, mostly due to intrinsic intensity fluctuations of the X-ray beam, leading to the need for averaging over multiple acquisitions. High-quality single-pulse EXAFS, under laser-shock compression, has also been demonstrated recently at APS (Das et al, 2020), but with insufficient energy resolution for the XANES region.…”

An FPGA-based Timing and Control System for the Dynamic Compression Sector

“…The DCS laser shock station allows users to compress millimeter-scale targets to multi-Mbar pressures over a duration of nanoseconds using the 100J UV laser system. During compression, xray diffraction [1] or EXAFS [2] measurements from a single x-ray pulse provide atomic scale structural information, while VISAR (Velocity Interferometer System for Any Reflector ) interferometry provides velocity measurements on the continuum scale. The timing of the x-ray probe is critical to the success of an experiment, as the probe timing must correspond to a desired shock state in the sample (e.g.…”

Single-shot X-ray absorption spectroscopy at X-ray free electron lasers

“…To overcome these limits, single-shot XAS capabilities have been developed at synchrotrons [16][17][18][19] , at XFELs [20][21][22] , and at facilities using optical laser-driven x-ray sources 23,24 . These developments are all based on a dispersive method that allows an entire spectral range to be collected at once, using dispersive optics and position sensitive detectors.…”