Current advances on Talbot–Lau x-ray imaging diagnostics for high energy density experiments (invited)

Abstract

Talbot–Lau x-ray interferometry is a refraction-based diagnostic that can map electron density gradients through phase-contrast methods. The Talbot–Lau x-ray deflectometry (TXD) diagnostics have been deployed in several high energy density experiments. To improve diagnostic performance, a monochromatic TXD was implemented on the Multi-Tera Watt (MTW) laser using 8 keV multilayer mirrors (Δθ/θ = 4.5%-5.6%). Copper foil and wire targets were irradiated at 1014–1015 W/cm2. Laser pulse length (∼10 to 80 ps) and backlighter target configurations were explored in the context of Moiré fringe contrast and spatial resolution. Foil and wire targets delivered increased contrast <30%. The best spatial resolution (<6 μm) was measured for foils irradiated 80° from the surface. Further TXD diagnostic capability enhancement was achieved through the development of advanced data postprocessing tools. The Talbot Interferometry Analysis (TIA) code enabled x-ray refraction measurements from the MTW monochromatic TXD. Additionally, phase, attenuation, and dark-field maps of an ablating x-pinch load were retrieved through TXD. The images show a dense wire core of ∼60 μm diameter surrounded by low-density material of ∼40 μm thickness with an outer diameter ratio of ∼2.3. Attenuation at 8 keV was measured at ∼20% for the dense core and ∼10% for the low-density material. Instrumental and experimental limitations for monochromatic TXD diagnostics are presented. Enhanced postprocessing capabilities enabled by TIA are demonstrated in the context of high-intensity laser and pulsed power experimental data analysis. Significant advances in TXD diagnostic capabilities are presented. These results inform future diagnostic technique upgrades that will improve the accuracy of plasma characterization through TXD.

Phase imaging of irradiated foils at the OMEGA EP facility using phase-stepping X-ray Talbot–Lau deflectometry

“…The postprocessing module of the Talbot Interferometry Analysis (TIA) code [ 5 ] , named the Talbot Numerical Tool (TNT) [ 11 ] , was used to separate the different Fourier components of both the data and reference images, following the procedure described in the previous section. This tool has been developed to automatically detect the peaks corresponding to the periodicity of the fringes in the Fourier spectra of noisy images, which was fundamental to detect and analyze the low-contrast fringes in the data presented.…”

“…Backlighter target geometry and orientation with respect to the incident laser will be explored to improve system spatial resolution and overall signal quality in combination with optimization of the laser parameters. The addition of a laterally graded multilayer mirror to the OMEGA EP-TXD will ensure monochromaticity of the X-ray backlighter radiation [ 11 ] by removing contributions from higher energy lines (such as the He or the K lines) and hot electron re-circulation, among others, which have shown to be detrimental to TXD diagnostic accuracy [ 35 ] . In addition, both TIA and its postprocessing module the TNT will be further developed to work with additional hydrodynamic codes and deliver real-time information, providing valuable insight to inform experimental campaigns.…”

“…In recent years, with the aim of imaging dense plasmas, there have been several efforts to adapt Talbot–Lau interferometry to high-power laser facilities [ 11 ] such as PALS [ 12 ] , the Multi-Terawatt (MTW) facility [ 13 ] and OMEGA EP [ 14 ] , as well as proof-of-concept experiments at lower-energy high-repetition rate lasers [ 4 ] . These experiments have permitted a thorough study of the optimal requirements for X-ray backlighting [ 15 ] , while also providing useful data for analysis tool development.…”