New experimental platforms at HED facilities can explore new physics regimes. High-resolution diagnostics and measurement innovation support model validation thus enabling deeper understanding of plasma processes. Shock compression plays a profound role in astrophysics, materials, high energy density, and planetary science. Accurate probing is challenging due to steep density gradients, sub- $\mu \mathrm{m}$ and -ns scales. Coherent X-ray sources such as X-ray Free Electron Lasers are a powerful tool to improve transparent media visualization (e.g., turbulent 3D structure, plasma flow contours) in combination with advanced refraction-based imaging. We describe a grating-based phase-contrast imaging platform (~200ns, $\left(>10^{13} ~\mathrm{W} / \text{cm}^{2}\right)$ Multi-Mbar compression in low-density aerogel and additively manufactured foams, seeking to extend shock dynamics description to non-homogeneous media, focusing on early compression stage in ICF. Shocked material density distribution captured development and evolution of distinct features with remarkable sensitivity, testing target density and design (e.g., lattice structure, interfaces). The shock front position was determined with sub- $\mu \mathrm{m}$ resolution, enabling instantaneous shock speed measurements along the shock tube. Experimental data agreement with hydrodynamic simulations provide insights into mechanisms for shock formation and evolution. In aerogels, shock front density $<10^{24} ~\text{cm}^{-3}$ was determined and <6x foam compression was detected within $<1 \mu ~\mathrm{m}$, behind a quasiuniform low-density region. In modulated targets, instability features were clearly resolved at $\sim 2 \times 10^{21} ~\text{cm}^{-2}$ areal density, enabling growth rate measurements. Multiple shocks were observed in 3D printed foams, indicating shock dynamics are dominated by lattice structures in additively manufactured foams. It was shown that, with high-fidelity probing, the MEC shocked-foam platform can be a valuable tool to systematically investigate plasma dynamics in shock-compressed foams.

The last decade has shown the great potential that X-ray Free Electron Lasers (FEL) have to study High Energy Density (HED) physics. Experiments at FELs have made significant breakthroughs in Shock Physics and Dynamic Diffraction, Dense Plasma Physics and Warm Dense Matter Science, using techniques such as isochoric heating, inelastic scattering, small angle scattering and X-ray diffraction. In addition, and complementary to these techniques, the coherent properties of the FEL beam can be used to image HED samples with high fidelity. We present new imaging diagnostics and techniques developed at the Matter in Extreme Conditions (MEC) instrument at Linac Coherent Light Source (LCLS) over the last few years. We show results in Phase Contrast Imaging geometry, where the X-ray beam propagates from the target to a camera revealing its phase, as well as in Direct Imaging geometry, where a real image of the sample plane is produced in the camera with a spatial resolution down to 200 nm. Last, we show an implementation of the Talbot Imaging method allowing both X-ray phase and intensity measurements change introduced by a target with sub-micron resolution.

Decades of research have investigated the mechanical properties of matter under extreme conditions, exploring how materials deform, yield, and fail when subjected to high strain rates. While plasticity codes and computational methods can provide atomic-scale precision, reliable experimental benchmarks are needed to validate these models. However, for decades only bulk and surface measurements (e.g., velocimetry and reflectivity) were available to the community, and data interpretation was mainly done relying on conventional plasticity models and drawing parallels with results obtained under quasi-hydrostatic conditions. In recent years the advent of X-ray free electron lasers has provided insight into the microscopic structure of shock-compressed matter, revealing substantial differences with static compression experiments. Information at the mesoscale was, however, still missing, and the onset and propagation of the deformation at this length-scale was only accessible using computational methods; in this paper we fill that void, providing experimental data at the relevant time- and length-scales. Here, we combine imaging and structural characterization in situ using a nanosecond pump laser coupled with a femtosecond X-ray probe in a novel experimental configuration at the LCLS. Our data provides a comprehensive characterization of the deformation of silicon, a simple, yet highly debated, model system for high-strength materials. Information spanning the macroscopic and mesoscopic scale down to the lattice level allows us to resolve and directly visualize the nucleation and growth of the high-pressure phase for the first time, providing a temporal constraint on its kinetics. These novel insights are crucial to unambiguously determine how silicon yields under shock-compression, as they are able to connect the structural evolution at the atomic level with the complex multi-wave dynamic observed at the macroscopic scale, reliably benchmarking decade-old theoretical predictions.

Single-shot two-dimensional (2D) phase retrieval (PR) can recover the phase shift distribution within an object from a single 2D x-ray phase contrast image (XPCI). Two competing XPCI imaging modalities often used for single-shot 2D PR to recover material properties critical for predictive performance capabilities are: speckle-based (SP-XPCI) and propagation-based (PB-XPCI) XPCI imaging. However, PR from SP-XPCI and PB-XPCI images are, respectively, limited to reconstructing accurately slowly and rapidly varying features due to noise and differences in their contrast mechanisms. Herein, we consider a combined speckle- and propagation-based XPCI (SPB-XPCI) image by introducing a mask to generate a reference pattern and imaging in the near-to-holographic regime to induce intensity modulations in the image. We develop a single-shot 2D PR method for SPB-XPCI images of pure phase objects without imposing restrictions such as object support constraints. It is compared against PR methods inspired by those developed for SP-XPCI and PB-XPCI on simulated and experimental images of a thin glass shell before and during shockwave compression. Reconstructed phase maps show improvements in quantitative scores of root-mean-square error and structural similarity index measure using our proposed method.

We measured correlated X-ray photons from parametric down conversion as a means of creating entangled X-rays. Using a Laue diffraction geometry, we measured the efficiency of this process from single crystal diamond samples.

Mesoscale imperfections, such as pores and voids, can strongly modify the properties and the mechanical response of materials under extreme conditions. Tracking the material response and microstructure evolution during void collapse is crucial for understanding its performance. In particular, imperfections in the ablator materials, such as voids, can limit the efficiency of the fusion reaction and ultimately hinder ignition. To characterize how voids influence the response of materials during dynamic loading and seed hydrodynamic instabilities, we have developed a tailored fabrication procedure for designer targets with voids at specific locations. Our procedure uses SU-8 as a proxy for the ablator materials and hollow silica microspheres as a proxy for voids and pores. By using photolithography to design the targets' geometry, we demonstrate precise and highly reproducible placement of a single void within the sample, which is key for a detailed understanding of its behavior under shock compression. This fabrication technique will benefit high-repetition rate experiments at x-ray and laser facilities. Insight from shock compression experiments will provide benchmarks for the next generation of microphysics modeling.

Inertial confinement fusion (ICF) holds increasing promise as a potential source of abundant, clean energy, but has been impeded by defects such as micro-voids in the ablator layer of the fuel capsules. It is critical to understand how these micro-voids interact with the laser-driven shock waves that compress the fuel pellet. At the Matter in Extreme Conditions (MEC) instrument at the Linac Coherent Light Source (LCLS), we utilized an x-ray pulse train with ns separation, an x-ray microscope, and an ultrafast x-ray imaging (UXI) detector to image shock wave interactions with micro-voids. To minimize the high- and low-frequency variations of the captured images, we incorporated principal component analysis (PCA) and image alignment for flat-field correction. After applying these techniques we generated phase and attenuation maps from a 2D hydrodynamic radiation code (xRAGE), which were used to simulate XPCI images that we qualitatively compare with experimental images, providing a one-to-one comparison for benchmarking material performance. Moreover, we implement a transport-of-intensity (TIE) based method to obtain the average projected mass density (areal density) of our experimental images, yielding insight into how defect-bearing ablator materials alter microstructural feature evolution, material compression, and shock wave propagation on ICF-relevant time scales.

Many questions regarding dynamic materials could be answered by using time-resolved ultra-fast imaging techniques to characterize the physical and chemical behavior of materials in extreme conditions and their evolution on the nanosecond scale. In this work, we perform multi-frame phase-contrast imaging (PCI) of micro-voids in low density polymers under laser-driven shock compression. At the Matter in Extreme Conditions (MEC) Instrument at the Linac Coherent Light Source (LCLS), we used a train of four x-ray free electron laser (XFEL) pulses to probe the evolution of the samples. To visualize the void and shock wave interaction, we deployed the Icarus V2 detector to record up to four XFEL pulses, separated by 1-3 nanoseconds. In this work, we image elastic waves interacting with the micro-voids at a pressure of several GPa. Monitoring how the material’s heterogeneities, like micro-voids, dictate its response to a compressive wave is important for benchmarking the performances of inertial confinement fusion energy materials. For the first time in a single sample, we have combined an ultrafast x-ray framing camera and four XFEL pulse train to create an ultrafast movie of micro-void evolution under laser-driven shock compression. Eventually, we hope this technique will resolve the material density as it evolves dynamically under laser shock compression.

We measure polarization-resolved fundamental, second, and third harmonic nonlinear Thomson scattering out the side of a laser focus with 1018 W/cm2. The separate measured polarization components are each associated with a distinct dimension of predicted electron figure-8 motion. Taken together, the measured angular emission patterns for the two polarizations unambiguously confirm the figure-8 motion. Electrons are donated from lowdensity helium (10−3 to 1 Torr) ionized early during the laser pulse. Time-resolved single-photon detection is used to distinguish signal from noise.

With an ultrafast framing camera, we image the propagation of a shock wave on the nanosecond time-scale. Four frame x-ray phase-contrast radiographs are acquired using the pulse train from an x-ray free electron laser.