An Extended X-Ray Absorption Fine Structure Spectroscopy Study of Iron and Iron Oxide

To increase our understanding of the formation and evolution of the Earth and iron-rich exoplanets, extended x-ray absorption fine structure (EXAFS) spectroscopy was used to characterize iron and iron oxides dynamically compressed to core Earth and super-Earth conditions. At the Omega Laser Facility, iron and iron oxides were ramp compressed to above 500 GPa and probed with a broadband x-ray source. The spatial and spectral behavior of the x-ray source was characterized using time integrating and time-resolved diagnostics. A new x-ray spectrometer was developed to improve the spectral resolution of the EXAFS measurement. By using a silicon mirror and new target geometry, EXAFS and VISAR (velocity interferometer system for any reflector) measurements were successfully carried out on the same shot, allowing for a complete and simultaneous equation-of-state measurement of pressure, density, and temperature. The temperature in the sample was determined from the EXAFS data by characterizing the ion positions in the crystal lattice.