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

Abstract

Characterizing materials at pressures of several megabars 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. The laser-driven shock compression technique is capable of simultaneously achieving conditions of several megabars and several thousand Kelvin, but the explored states are too hot to be representative of planetary interiors. Double-shock compression provides an alternative to probe 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 generalized Rankine-Hugoniot relations together with a self-impedance mismatch technique. A validation experiment has been performed at the LULI2000 facility (École Polytechnique, France) on a water sample. A temperature 63% lower than along the principal Hugoniot has been obtained at 1.9 Mbar.