Dynamic reflectance measurements of shocked materials

Temperature measurements are critical to equation of state development, but are notoriously difficult to perform and interpret. Infrared pyrometry is a valuable temperature diagnostic for a wide range of dynamic compression studies, but the technique is of limited use without knowledge of material emissivity. Although emissivity can be inferred from reflectance measurements---usually at ambient conditions---the manner in which this quantity changes with pressure, temperature, surface condition, and material phase is unknown. This presentation describes an emissivity characterization study of shock-compressed metal films. Real-time, infrared reflectance measurements are performed by coupling light from the VUV ring of the National Synchrotron Light Source to a gas gun system. As the samples are shock compressed, specular reflectance changes are measured using fast near- and mid-infrared detectors capable of tracking individual synchrotron pulses. This research provides data that can be used to constrain dynamic emissivity changes, and may lead to a set of emissivity standards that can be applied to any material.