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Measurements of silver K-shell and bremsstrahlung emission from thin-foil laser targets as a function of laser prepulse energy are presented. The silver targets were chosen as a potential 22 keV backlighter source for the National Ignition Facility Experiments. The targets were irradiated by the Titan laser with an intensity of 8 x 1017 W/cm² with 40 ps pulse length. A secondary nanosecond timescale laser pulse with controlled, variable energy was used to emulate the laser prepulse. Results show a decrease in both Kα and bremsstrahlung yield with increasing artificial prepulse. Radiation hydrodynamic modeling of the prepulse interaction determined that the preplasma and intact target fraction were different in the three prepulse energies investigated. Interaction of the short pulse laser with the resulting preplasma and target was then modeled using a particle-in-cell code PSC which explained the experimental results. The relevance of this work to future Advanced Radiographic Capability laser x-ray backlighter sources is discussed. [ABSTRACT FROM AUTHOR]

Measurements of Kα radiation yield and x-ray bremsstrahlung emission from thin-foil silver targets are presented. The targets were irradiated by a short pulse laser with intensities from 5×1016 to 1018 W/cm2 at 40 ps. Single hit charge-coupled device detectors, differential filter-stack detectors, and a crystal spectrometer were used to investigate the angular distribution of the Kα and bremsstrahlung x-rays. This study is the first to use a broadband detector to estimate the absolute numbers of Kα photons and to determine Kα to bremsstrahlung ratios. The relevance of this work in the context of x-ray diffraction and x-ray radiography is discussed. [ABSTRACT FROM AUTHOR]

The Bremsstrahlung and K-shell emission from 1×1×1 mm3 planar targets irradiated by a short-pulse 3×1018–8×1019 W/cm2 laser were measured. The Bremsstrahlung was measured using a filter stack spectrometer with spectral discrimination up to 500 keV. K-shell emission was measured using a single photon counting charge coupled device. From Monte Carlo modeling of the target emission, conversion efficiencies into 1–3 MeV electrons of 3%–12%, representing 20%–40% total conversion efficiencies, were inferred for intensities up to 8×1019 W/cm2. Comparisons to scaling laws using synthetic energy spectra generated from the intensity distribution of the focal spot imply slope temperatures less than the ponderomotive potential of the laser. Resistive transport effects may result in potentials of a few hundred kV in the first few tens of microns in the target. This would lead to higher total conversion efficiencies than inferred from Monte Carlo modeling but lower conversion efficiencies into 1–3 MeV electrons. [ABSTRACT FROM AUTHOR]

We present scaled demonstrations of backlighter sources, emitting bremsstrahlung x rays with photon energies above 75 keV, that we will use to record x-ray Compton radiographic snapshots of cold dense DT fuel in inertial confinement fusion implosions at the National Ignition Facility (NIF). In experiments performed at the Titan laser facility at Lawrence Livermore National Laboratory, we measured the source size and the bremsstrahlung spectrum as a function of laser intensity and pulse length from solid targets irradiated at 2×1017–5×1018 W/cm2 using 2–40 ps pulses. Using Au planar foils we achieved source sizes down to 5.5 μm and conversion efficiencies of about 1×10-13 J/J into x-ray photons with energies in the 75–100 keV spectral range. We can now use these results to design NIF backlighter targets and shielding and to predict Compton radiography performance as a function of the NIF implosion yield and associated background. [ABSTRACT FROM AUTHOR]