$K$-Shell Photoabsorption Edge of Strongly Coupled Matter Driven by Laser-Converted Radiation

The first observation of the $K$-shell photoabsorption edge of strongly coupled matter with an ion-ion coupling parameter of about 65 generated by intense x-ray radiation-driven shocks is reported. The soft x-ray radiation generated by laser interaction with a “dog bone” high-$Z$ hohlraum is used to ablate two thick CH layers, which cover a KCl sample, to create symmetrical inward shocks. While the two shocks impact at the central KCl sample, a highly compressed KCl is obtained with a density of 3–5 times solid density and a temperature of about 2–4 eV. The photoabsorption spectra of chlorine near the $K$-shell edge are measured with a crystal spectrometer using a short x-ray backlighter. The redshift of the $K$ edge up to 11.7 eV and broadening of 15.2 eV are obtained for the maximum compression. A comparison of the measured redshifts and broadenings with dense plasma calculations are made, and it indicates potential improvements in the theoretical description.

Figure 1

(a) Schematic of the experimental setup. (b) Half-sample sandwich target. (c) Typical spectral image.

Figure 2

(a) The modified temporal behavior of the radiation at the sample, with a peak temperature of 90 eV. (b) The simulated evolution of temperature and density of the KCl in the $\mathrm{CH}/\mathrm{KCl}/\mathrm{CH}$ multilayer foil as compressed by the near-Plank x-ray radiation-driven colliding shocks. The solid pentacles refer to the temperatures deduced from the measured $K$ edge broadening at different time delays of 2.38, 2.78, and 3.14 ns. (c) The $\rho$ and $T$ spatial profile from the center of the KCl sample to the edge at time delays.

Figure 3

Measured backlighter x-ray source spectrum and $K$-shell edge absorption spectra of the compressed KCl sample at different time delays of 2.38, 2.78, and 3.14 ns. As a comparison, the $K$-shell edge absorption spectrum for a cold KCl sample (with the eight heating laser beams off) is also presented at the bottom.

Figure 4

(a) Calculated total shifts of the $K$-shell absorption edge and the three contributions as functions of the density of the KCl sample compressed by the radiation-driven colliding shocks using a plasma model. (b) Comparison of the experimental $K$-edge shift results (solid pentacle represents our results, purple circle represents Bradley’s result) with the calculation curve along the compressed state of the KCl sample in this experiment based on the plasma model. Also presented are the calculated shifts of the Cl $K$-shell absorption edge as a function of the density for temperatures of 0 (blue dashed line) and 5 eV (red dashed line).