TT-06 Reflectivity in Dense Xe Plasma

Abstract

Reflectivity can be used as a diagnostic tool for the investigation of dense plasma and its metallization. Measurements in shock wave produced dense Xenon plasmas at a temperature of around 30 000 K have been performed with a laser beam of three wavelengths: 1.06 µm, 0.694 µm and 0.532 µm [1]. A strong increase of the reflectivity indicating an onset of metallic behaviour was observed for densities above the critical density n cr e = ɛ0meω 2 L /e2, where the plasma frequency coincides with the laser frequency. Assuming a step-like shock front, the reflectivity is directly related to the dielectric function via the Fresnel formula [2]. The dielectric function is calculated from the generalized Drude formula ɛ(ω) = 1 − ω2 pl. (1) ω[ω + iν(ω)] The collision frequency ν(ω) was determined from a frequency dependent dynamical collision frequency for electronion collisions taking into account dynamical screening and strong collisions. We also considered electron-electron collisions via a renormalization factor as well as electron-atom collisions. Bound state transitions contribute to the dielectric function following a cluster expansion. Despite these consistent approximations, the results for the collision frequency overestimate the reflectivity. Note, that molecular dynamics simulations also give an overestimation. In conclusion, a theoretical approach assuming a step like shock wave front is not able to explain the low reflectivity even above the critical density. profile naF(ne, z) for every final value of ne in the produced plasma with z the distance from the high density region. An asymmetric Fermi profile [3] naF(ne, z) = ne eY (z), + 1 (3) Y (z) = −

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