Probing local and electronic structure in Warm Dense Matter: single pulse synchrotron x-ray absorption spectroscopy on shocked Fe

Abstract

Understanding Warm Dense Matter (WDM), the state of planetary interiors, is a new frontier in scientific research. There exists very little experimental data probing WDM states at the atomic level to test current models and those performed up to now are limited in quality. Here, we report a proof-of-principle experiment that makes microscopic investigations of materials under dynamic compression easily accessible to users and with data quality close to that achievable at ambient. Using a single 100 ps synchrotron x-ray pulse, we have measured, by K-edge absorption spectroscopy, ns-lived equilibrium states of WDM Fe. Structural and electronic changes in Fe are clearly observed for the first time at such extreme conditions. The amplitude of the EXAFS oscillations persists up to 500 GPa and 17000 K, suggesting an enduring local order. Moreover, a discrepancy exists with respect to theoretical calculations in the value of the energy shift of the absorption onset and so this comparison should help to refine the approximations used in models.

Comparative study of the influence of pulsed and continuous wave laser heating on the mobilization of carbon and its chemical reaction with iron in a diamond anvil cell

“…2) is a characteristic feature of ε-Fe. 23,24 It was recently recognized that vanishing of this shoulder after heating indicates a chemical reaction between iron and…”

Ultra-High Pressure Dynamic Compression of Geological Materials

“…Development of similar capabilities for EXAFS measurements are being carried out at NIF (Coppari et al, 2017). XAFS measurements have also been reported on laser-driven samples at pressure extending to the multimegabar range using other X-ray sources including laser-driven backlighter foils (Denoeud et al, 2014(Denoeud et al, , 2016a, synchrotrons (Torchio et al, 2016), and free electron lasers (Harmand et al, 2015).…”

“…Iron has also been used in a proof-of-principle experiment to demonstrate EXAFS capabilities on laser-shocked iron using a synchrotron X-ray source. In experiments performed at the European Synchrotron Radiation Facility, iron was shock compressed to as high as 500 GPa using a 35-J laser focused down to a 90-µm spot size (Torchio et al, 2016). Synchrotron X-rays were dispersed and focused on the sample using a curved crystal.…”

Targets for high repetition rate laser facilities: needs, challenges and perspectives

“…In addition, if a sample is too thick, release waves from the ablating material may dramatically reduce the pressure in a portion of the sample. A sandwich target can also be designed to reach off-Hugoniot states or to sustain the peak pressure for longer time (few ns) [21] . In this case, the sample can be embedded between two layers of a material with impedance similar to the studied sample.…”