Measurements of Ionic Structure in Shock Compressed Lithium Hydride from Ultrafast X-Ray Thomson Scattering

We present the first ultrafast temporally, spectrally, and angularly resolved x-ray scattering measurements from shock-compressed matter. The experimental spectra yield the absolute elastic and inelastic scattering intensities from the measured density of free electrons. Laser-compressed lithium-hydride samples are well characterized by inelastic Compton and plasmon scattering of a $K\mathrm{\text{−}}\alpha$ x-ray probe providing independent measurements of temperature and density. The data show excellent agreement with the total intensity and structure when using the two-species form factor and accounting for the screening of ion-ion interactions.

Figure 1

(a) Schematic of the experimental setup. Here, short-pulse laser produced Ti $K\mathrm{\text{−}}\alpha$ x rays are scattered from LiH targets that are compressed using a second long-pulse drive beam. Also shown are raw data for scattering at about 95° and 40°. (b) Radiation-hydrodynamic calculations of the mass density, plotted as a function of time and target thickness, where $t=0$ denotes the start of the drive beam. The predicted compression at $t_0=4.5\mathrm{ns}$ is about $\rho /{\rho }_o=2.7$. (c) Profiles of the measured drive-beam waveform (blue) and a delayed short-pulse beam that was used to create the x-ray probe (red).

Figure 2

X-ray Thomson scattering data from shock-compressed LiH targets using Ti $K\mathrm{\text{−}}\alpha$ x rays in the noncollective scattering regime. The single-shot data at $95\pm 10°$ show elastic scattering at 4.5 keV and inelastic Compton scattering at 4.45 keV, which allows characterization of the electron density and temperature. Theoretical fits to the experimental data are plotted for various densities and temperatures (inset). Best theoretical fits to the experimental data indicate temperatures and electron densities of $1.7\mathrm{eV}\pm 20\%$ and $1.6\times {10}^{23}{\mathrm{cm}}^{-3}\pm 20\%$.

Figure 3

Measurements of the elastic scattering intensity as a function of the scattering wave vector from shock-compressed LiH targets using Ti $K\mathrm{\text{−}}\alpha$ x rays (black points) compared to different theoretical models and simulations (see text).