Characterising equation of state and optical properties of dynamically pre-compressed materials

TL;DR

This paper introduces a new method to characterize the equation of state and optical properties of materials under high-pressure, moderate-temperature conditions relevant to planetary interiors, using double-shock compression and optical diagnostics without hydrodynamical simulations.

Contribution

The authors develop a novel experimental approach combining generalized Rankine-Hugoniot relations and impedance mismatch techniques to measure thermodynamic states in double-shocked materials.

Findings

Achieved 60% lower temperature than principal Hugoniot at 7.5 Mbar.

Validated method on α-quartz at LULI2000 facility.

Demonstrated control and measurement of double-shocked states.

Abstract

Characterising materials at pressures of several megabar and temperatures of a few thousand Kelvin is critical for the understanding of the Warm Dense Matter regime and to improve planetary models as these conditions are typical of planets' interiors. Today, laser-driven shock compression is the only technique to achieve multimegabar pressures, but the associated temperatures are too high to be representative of planetary states. Double-shock compression represents an alternative to explore lower temperatures. Here we present a method to create well-controlled double-shocked states and measure their thermodynamic state and optical reflectivity using standard optical diagnostics (Doppler velocimetry and optical pyrometry) in a laser-driven shock experiment. This method, which does not require the support of hydrodynamical simulations, is based on the application of generalised Rankine-Hugoniot relations together with a self impedance mismatch technique. A validation experiment has been performed at the LULI2000 facility (\'Ecole Polytechnique, France) on a sample of $\alpha$-quartz. A temperature $60 \%$ lower than along the principal Hugoniot has been obtained at 7.5 Mbar.