Direct density measurement of shock-compressed iron using hard x rays generated by a short laser pulse

Advanced high resolution x-ray diagnostic for HEDP experiments

High resolution X-ray imaging is crucial for many high energy density physics (HEDP) experiments. Recently developed techniques to improve resolution have, however, come at the cost of a decreased field of view. In this paper, an innovative experimental detector for X-ray imaging in the context of HEDP experiments with high spatial resolution, as well as a large field of view, is presented. The platform is based on coupling an X-ray backligther source with a Lithium Fluoride detector, characterized by its large dynamic range. A spatial resolution of 2 µm over a field of view greater than 2 mm² is reported. The platform was benchmarked with both an X-ray free electron laser (XFEL) and an X-ray source produced by a short pulse laser. First, using a non-coherent short pulse laser-produced backlighter, reduced penumbra blurring, as a result of the large size of the X-ray source, is shown. Secondly, we demonstrate phase contrast imaging with a fully coherent monochromatic XFEL beam. Modeling of the absorption and phase contrast transmission of X-ray radiation passing through various targets is presented.

High-energy X-ray radiography of laser shock loaded metal dynamic fragmentation using high-intensity short-pulse laser

The dynamic fragmentation of shock-loaded high-Z metal is of considerable importance for both basic and applied science. The areal density and mass-velocity distribution of dynamic fragmentation are crucial factors in understanding this issue. Experimental methods, such as pulsed X-ray radiography and proton radiography, have been utilized to obtain information on such factors; however, they are restricted to a complex device, and the spatial resolution is in the order of 100 μm. In this work, we present the high-quality radiography of the dynamic fragmentation of laser shock-loaded tin, with good two-dimensional (2D) spatial resolution. Dynamic fragmentation is generated via high-intensity ns-laser shock-loaded tin. A high-energy X-ray source in the 50-200 keV range is realized by the interaction of a high-intensity ps-pulse with an Au microwire target, attached to a low-Z substrate material. A high 2D resolution of 12 μm is achieved by point-projection radiography. The dynamic-fragmentation radiography is clear, and the signal-to-noise ratio is sufficiently high for a single-shot experiment. This unique technique has potential application in high-energy density experiments.

Laser-driven shock waves studied by x-ray radiography

Multimegabar laser-driven shock waves are unique tools for studying matter under extreme conditions. Accurate characterization of shocked matter is for instance necessary for measurements of equation of state data or opacities. This paper reports experiments performed at the LULI facility on the diagnosis of shock waves, using x-ray-absorption radiography. Radiographs are analyzed using standard Abel inversion. In addition, synthetic radiographs, which also take into account the finite size of the x-ray source, are generated using density maps produced by hydrodynamic simulations. Reported data refer to both plane cylindrical targets and hemispherical targets. Evolution and deformation of the shock front could be followed using hydrodynamic simulations.

Improvement of density resolution in short-pulse hard x-ray radiographic imaging using detector stacks

We demonstrate that stacking several imaging plates (IPs) constitutes an easy method to increase hard x-ray detection efficiency. Used to record x-ray radiographic images produced by an intense-laser driven hard x-ray backlighter source, the IP stacks resulted in a significant improvement of the radiograph density resolution. We attribute this to the higher quantum efficiency of the combined detectors, leading to a reduced photon noise. Electron-photon transport simulations of the interaction processes in the detector reproduce the observed contrast improvement. Increasing the detection efficiency to enhance radiographic imaging capabilities is equally effective as increasing the x-ray source yield, e.g., by a larger drive laser energy.

Commissioning of a frequency-resolved optical gating system at the OMEGA EP laser facility: SpecFROG

We present the design and commissioning of a new single-shot, frequency-resolved optical gating system on the OMEGA EP laser facility - dubbed "SpecFROG" - for characterizing the instantaneous intensity and phase of ∼10 ps pulses used to study ultra-intense laser-plasma interactions. A polarization-gating geometry is employed to ensure tha the diagnostic is broadband and has unambiguous time directionality. SpecFROG is capable of characterizing ∼10 s of mJ pulses with durations between 0.5-25 ps with ≲285 fs geometrical temporal blurring and ∼0.1% spectral shift resolutions over an adjustable total spectral shifting window of ∼15% of the carrier wavelength λo; configurations currently exist for both the fundamental (1ω, λo = 1.054 μm) and second harmonic (2ω, λo = 0.527 μm) of the EP pulse. Initial specular reflectivity measurements of the ∼1 kJ, ∼10 ps OMEGA EP laser off solid density aluminum targets suggest drastically different scalings for specular pulse properties compared to picosecond-scale pulses of comparable intensities.