S. Moon

Electronic conduction in shock-compressed water

The optical reflectance of a strong shock front in water increases continuously with pressure above 100 GPa and saturates at ∼45% reflectance above 250 GPa. This is the first evidence of electronic conduction in high pressure water. In addition, the water Hugoniot equation of state up to 790 GPa (7.9 Mbar) is determined from shock velocity measurements made by detecting the Doppler shift of reflected light. From a fit to the reflectance data we find that an electronic mobility gap ∼2.5 eV controls thermal activation of electronic carriers at pressures in the range of 100–150 GPa. This suggests that electronic conduction contributes significantly to the total conductivity along the Neptune isentrope above 150 GPa.

Absolute x-ray yields from laser-irradiated germanium-doped low-density aerogels

The x-ray yields from laser-irradiated germanium-doped ultra-low-density aerogel plasmas have been measured in the energy range from sub-keV to ≈15 keV at the OMEGA laser facility at the Laboratory for Laser Energetics, University of Rochester. The targets’ x-ray yields have been studied for variation in target size, aerogel density, laser pulse length, and laser intensity. For targets that result in plasmas with electron densities in the range of ≈10% of the critical density for 3ω light, one can expect 10–11 J/sr of x rays with energies above 9 keV, and 600–800 J/sr for energies below 3.5 keV. In addition to the x-ray spectral yields, the x-ray temporal waveforms have been measured and it is observed that the emitted x rays generally follow the delivered laser power, with late-time enhancements of emitted x-ray power correlated with hydrodynamic compression of the hot plasma. Further, the laser energy reflected from the target by plasma instabilities is found to be 2%–7% of the incident energy for indiv...

Properties of fluid deuterium under double-shock compression to several Mbar

The compressibility of fluid deuterium up to several Mbar has been probed using laser-driven shock waves reflected from a quartz anvil. Combining high-precision (∼1%) shock velocity measurements with the double-shock technique, where differences in equation of state (EOS) models are magnified, has allowed better discrimination between theoretical predictions in the second-shock regime. Double-shock results are in agreement with the stiffer EOS models—which exhibit roughly fourfold single-shock compression—for initial shocks up to 1 Mbar and above 2 Mbar, but diverge from these predictions in between. Softer EOS models—which exhibit sixfold single-shock compression at 1 Mbar—overestimate the reshock pressure for the entire range under study.

Extremely compact soft X-ray lasers based on capillary discharges

Extremely compact high repetition rate soft X-ray lasers based on capillary discharge excitation have demonstrated average powers of a few milliWatt at 46.9 nm, milli-Joule-level pulse energy, peak spectral brightness several orders of magnitude larger than third-generation synchrotron beam lines, and excellent spatial coherence. Examples of the use of a capillary discharge soft X-ray laser in dense plasma diagnostics and laser ablation of materials are summarized.

Application of extremely compact capillary discharge soft x-ray lasers to dense plasma diagnostics

Table-top capillary discharge soft x-ray lasers combine the advantages of a small size and a high repetition rate with an extremely high brightness similar to that of their laboratory-size predecessors. When utilized to probe high density plasmas their short wavelength results in a higher critical density, reduced refraction, decreased free-electron absorption, and higher resolution as compared to optical probes. These characteristics allow the design of experiments capable of measuring the evolution of plasmas with density–scale length products that are outside the reach of optical lasers. This paper reviews the use of a 46.9 nm wavelength Ne-like Ar capillary discharge table-top laser in dense plasma diagnostics, and reports soft x-ray laser interferometry results of spot-focus Nd:YAG laser plasmas created at moderate irradiation intensity (∼7×1012 W cm−2) with ∼13 ns pulse width duration laser pulses. The measurements produced electron density maps with densities up to 0.9×1021 cm−3 that show the devel...

Numerical studies of transient and capillary x-ray lasers and their applications

During recent months we have continued investigations of many different aspects of x-ray lasers to characterize and improve the source and applications. This work has included temporal characterization of existing laser-heated x-ray lasers under a wide range of pumping conditions. We have also looked into more details at different applications of x-ray lasers among which was the interferometry of laser-produced and capillary discharge plasmas in several irradiation conditions for different target Z materials. The reduction of pump energy remains the most important for the generation of new compact x-ray lasers. Numerical studies show that there are some ways to improve several of the key parameters of x-ray lasers specifically repetition rates and efficiency.

Experiments using laser-driven shockwaves for EOS and transport measurements

Laser-driven shocks have broken new ground in providing data on strongly coupled systems. One example is the measurements of the Hugoniot of hydrogen isotopes to over 300 GPa and the clear signature of metallic behavior at pressures of 60 GPa. The resulting fluid is strongly coupled (Γ > 10) and probably composed of ions, atoms, and molecules - a very difficult system to understand. The latest interpretation of these measurements is discussed. In addition, recent shock measurements on the hydrogen-bonded compound water - both EOS and reflectivity - are shown. The metallic signature for water is very different than that of hydrogen.

A Neutron Star Atmosphere in the Laboratory with Petawatt Lasers

We discuss the preliminary estimates to create Neutron Star atmospheric conditions in the laboratory and the possibility of generating photon bubbles. The minimal requirements for photonbubble instability could potentially be met with a properly configured 10 ps petawatt laser experiment. The high energy (multi-MeV) electrons generated by an ultra-intense laser interacting with a foil are coupled to the electrons in the solid to heat the entire solid generating high thermal temperatures. Small amounts of matter could potentially be heated to ∼1 keV temperatures with large radiation temperature. Additionally, 2-D PIC simulations show large B-fields on both the front and back of these targets with B fields consistent with experiments using the petawatt at Rutherford Appleton Laboratory (Tatarakis, M. et al.: 2002c, Nature 415, 280).

Satellite and opacity effects on resonance line shapes produced from short-pulse laser heated foils

Abstract We measure the He-like, time-resolved emission from two types of thin foils (1) consisting of 250 A of carbon together with 250 A of aluminum and (2) 500 A aluminum, illuminated with a 150 fs laser pulse at an intensity of 10 19 W / cm 2 . Dielectronic satellite contributions to the resonance transitions 1s 2 – 1 s 2 p ( 1 P ) , 1s 2 – 1 s 3 p ( 1 P ) , and 1s 2 – 1 s 4 p ( 1 P ) are modeled using the configuration-averaged code AVERROES and is found to be significant for all three resonance lines. The effects of opacity are inferred from the data and found to be significant only in the 1s 2 – 1 s 2 p ( 1 P ) .

Characterization of time resolved, buried layer plasmas produced by ultrashort laser pulses

Abstract We report on the characterization of plasmas produced by ultrashort laser irradiation of 500 A thick layers of NaF buried at varying depths in plastic to reduce plasma gradients. The targets are irradiated with 130 fs , ≈170 mJ laser pulses (λ=400 nm ) at an intensity of ≈2×10 18 W cm −2 . The data are spectrally and temporally resolved, with resolutions of λ/Δλ≈1000 and ≳500 fs , respectively. We use X-ray emission spectroscopy to assess the electron density, Ne, and temperature, Te, in the plasma. The density is measured from Stark broadened line profiles of the He-like 1 1S– 3 1 P , He β , and H-like Lyβ lines of Na, while the temperature is determined from the intensity ratio of Na Heβ to Lyβ, and also from the dielectronic satellites to these lines. We find peak densities and temperatures of ≳10 23 cm −3 and ≈400 eV , respectively, at 2– 4 ps after the laser pulse. The plasma conditions plateau near these values for 5 ps after that. Atomic data for the kinetics simulations are generated with the HULLAC suite of codes. The Stark broadened line profiles, with full accounting of satellite transitions, are computed with the TOTAL code. Self-absorption effects are included along the observation line of sight using the radiation transport code CRETIN. Steady-state, non-LTE equilibrium plasma conditions are demonstrated suggesting that buried-layer experiments can be used as a test bed to study equation of state and opacity properties in hot, near-solid density matter.