An experiment shows that equations of state of solid matter at pressure P= 10–50 Mbar can be studied by using lasers with pulse energy E≈100J. Laser beams smoothed by phase-zone plates produced high quality, planar shock waves in two-step, two-material targets, allowing simultaneous measurements of the shock velocities in the two materials. By the use of the impedance-matching technique, the relative consistency of the equations of state of these materials can be tested, or a relative equation of state data can be measured. Pressures higher than 35 Mbar were achieved in gold
A study on preheating effects in laser-driven shock waves is presented. Two different diagnostics were used: the color temperature measurement deduced by recording the target rear side emissivity in two spectral bands, and the rear surface reflectivity measurement by using a probe beam. In order to test the response of the two diagnostics to the preheating, three types of targets characterized by different radiative properties were used. The greater sensitivity of the second diagnostic compared with the first was demonstrated. A model which calculates the reflectivity using a one-dimensional hydrodynamic code data was developed. In this model, the wave propagation equations in the expanding plasma using an appropriate model for the electron–ion collision frequency applicable to the cold solid-hot plasma transition were solved. The comparison between the calculated and measured reflectivities allows us to estimate the preheating process.
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