(a) Schematic of the experimental configuration. An ultrashort (10 ps), monoenergetic , x-ray probe is generated via ultra-short-pulse laser irradiation of a titanium foil. The x rays interact with matter that is compressed by 6 ns long shaped laser pulse. The x-ray Thomson scattering spectrum shows inelastic scattering on plasmons and elastic Rayleigh scattering features. (b) Waveforms of the compression (blue) and probe (red) laser beams. The shaped compression beam drives a slow intensity shock into the LiH with a low intensity foot followed by a stronger shock with a higher intensity peak . The evolution of the shocks is measured at various times by changing the delay between the short-pulse probe laser and the long-pulse pump beam. (c) Radiation hydrodynamic modeling indicates coalescence of the shock waves at from the launch of the compression beam.
Conversion efficiency of laser energy into Ti -alpha radiation as a function of varying short-pulse probe laser intensity. Conversion efficiencies for a pulse width of 0.5 ps were comparable to that of 5 ps pulse widths, but the latter was used due to restrictions on available laser energy for a 0.5 ps laser pulse width.
Measured x-ray scattering spectrum from shocked LiH, showing elastic Rayleigh scattering and inelastic plasmon scattering features, with theoretical fits to the experimental data. At (top), the plasmon energy shift of 24 eV indicates three times compression, while the intensity of the elastic scattering feature shows heating to temperatures of 2.2 eV. Earlier in time, before the launch of the second strong shock , elastic scattering is mainly observed (middle), as demonstrated when compared to the source spectrum (bottom). The observation of plasmons at indicates the transition to the metallic free electron plasma in solid density LiH.
(a) Experimental scattering of Ti -alpha rays from compressed LiH, 7 ns after the first of two shocks was launched into the solid density target, with simulated theoretical spectra. Sensitivity of ionization state changes in the theoretical fit to the experimental data is shown with the best fit (blue) where , compared to fits with (red). Here, the temperature and density, 2.2 eV and , respectively, are held constant. (b) Sensitivity of theoretical fits to the experimental spectra for varying temperatures and ionization states, . RMS differences are color coded for given temperature and combinations, where the centered dark red island is a range of possible best fits. The error of this fitting method to the experimental data is ±10% for the ionization state .
(a) Experimental scattering of Ti -alpha x rays from compressed LiH, 7 ns after the first of two shocks was launched into the solid density target, with simulated theoretical spectra. Sensitivity of density changes in the theoretical fit to the experimental data is shown with the best fit (black) at , compared to fits at and (blue and green curves). Here, the temperature and ionization state, 2.2 eV and , respectively, are held constant. (b) Sensitivity theoretical fits to the experimental spectra for varying temperatures and electron densities. RMS values are color coded for given temperature and density combinations, where the centered black island is a range of possible best fits. The error of this fitting method to the experimental data is about ±10% for temperature and electron density.
(a) Temperature of the shocked LiH as function of time, where denotes the start of the compression beam, from x-ray Thomson scattering measurements (red) and from radiation-hydrodynamic modeling using different EOS models. The range of temperatures plotted for each model accounts for LiOH surface impurities (lower bounds) to no impurities (upper bounds). The experiments and calculations demonstrate efficient heating by shock coalescence with small differences in shock timing that can be resolved with the short x-ray pulses. (b) Sensitivity of theoretical fitting to the experimental data for varying temperature. The intensity of the elastic scattering feature increases with increasing temperature, from dependence on the ion-ion structure factor.
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