X-ray emission spectroscopy (XES) and optical Thomson scattering (OTS) are two of the most indispensable diagnostics for characterization of plasma parameters such as Te and ne in intense laser-produced plasmas (LPPs), but both can also provide weighted-average values owing to the line-of-sight, space, and time-integrated effects of optical/X-ray diagnostic techniques, which has not been thoroughly investigated. In this work, for the first time, the consistency and discrepancy between Te from XES and OTS are examined using intense lasers with a large focal spot to irradiate the smaller tip of a cylindrically symmetric titanium wire. Experimental results reveal that Te profiles derived from the two methods are approximately consistent in the earlier period of 1 ns, but exhibit different trends with increasing time. In addition, the impacts of the three integration effects on the interpretation of Te are assessed through an analysis of three types of XES methods, namely, time- and space-resolved, time-resolved but space-integrated, and time-integrated but space-resolved. Our findings indicate that the line-of-sight integration effect causes uncertainties of less than 5% in the electron temperature of corona LPPs, time-integrated XES can replace time-resolved measurements with an uncertainty of 10% for 1–2 ns laser duration, and space-integrated XES reflects the high-temperature region within 200 μm in front of the target surface, ∼10% lower than the maximum. These insights establish a foundation for the applications of experimental data in LPPs, particularly in the fields of laser-driven inertial confinement fusion and high-energy-density physics.
Over the last decade, frequency-domain in situ high-pressure nuclear magnetic resonance (NMR) spectroscopy in diamond anvil cells (DACs) has been employed as a structural and electronic probe of condensed matter systems at pressures well into the megabar range. However, extensive spin interactions and sample heterogeneities under pressure often lead to significant spectral overlap, inhibiting independent observation of chemically similar spin subspecies in the same sample. In this work, we introduce a time-domain relaxometry framework specifically suited for DAC experiments. Experimental flexibility and operational robustness are benchmarked on three hydrogen-rich molecular solids at pressures up to 72 GPa. We demonstrate that T-1-T-2 relaxometry can separate distinct proton populations in relaxation space even when the corresponding frequency-domain spectra are strongly broadened and overlapping, thereby establishing a practical route to relaxation-based high-pressure NMR analysis in molecular solids.
P2 is the remaining principal asymmetry in laser-driven hohlraums. A simple analytic model for P2 asymmetry on the Shenguang 100 kJ laser facility is presented, which is based on hohlraum geometry, wall albedo, plasma expansion, and shell velocity. The calculated P2 asymmetry from the model is in reasonably good agreement with experimental data from pre-pulse, shell flight and stagnation stages. The P2 model appears to capture the essential physics governing drive symmetry and has been implemented to guide new symmetric implosion designs, enabling a more rapid convergence to a symmetric implosion than the conventional trial-and-error approach.
Laser-driven proton acceleration has attracted considerable interest owing to its appealing potential in versatile applications including cancer therapy. Proton energies depend critically on the on-target intensities, yet the detrimental impact of focal spot degradation induced by spatiotemporal couplings on the acceleration remains insufficiently elucidated. In this study, we demonstrate that residual angular chirp (AC), stemming from minor misalignments of the grating compressor in a Petawatt-class laser system, acts as a critical bottleneck for proton acceleration. Experimental results reveal that even around 100 microradians of grating misalignment induces substantial focal-spot elongation and a pronounced reduction in peak intensity. By implementing an in situ spectral-blocking diagnostic, we effectively eliminated the residual AC and restored a near-diffraction-limited focus. This optimization led to a significant recovery of the on-target intensity, resulting in a twofold increase in the proton cutoff energy. Our work presents a successful demonstration of diagnosing and eliminating residual AC. This provides a practical reference for generating high-energy proton beams and supporting their diverse applications in a PW-class laser.
We propose an all-optical configuration for the integrated generation, collimation, and acceleration of positrons with laser–electron beam interaction in a channel target. The electromagnetic fields driven by a Doppler-boosted laser within the channel yield a high-collimated dense positron bunch (with a peak density of ∼1028 m−3 and a duration of ∼27 fs). With the channel target, the beam divergence angle (FWHM) is decreased from 40° to 23°, and the monoenergetic peak is expected to upshift to hundreds of MeV. Moreover, automatic spatial and spectral separation between positrons and background electrons is also achieved, providing a promising scheme for future high-quality positron generation in compact integrated devices.
Enhancement of betatron X-ray radiation produced in laser–plasma accelerators has previously been achieved by increasing the transverse oscillation amplitude of accelerated electrons in a tilted-shock traversal. This article reports on a simultaneous analysis of the properties of the betatron radiation and the trajectories of the relativistic electrons. The correlations of their parameters indicate new opportunities for improving betatron sources.
We demonstrate a self-seeded quantum electrodynamics (QED) cascade driven by a single 100 PW laser pulse reflected from a curved plasma mirror. Three-dimensional particle-in-cell simulations show that the reflected field self-injects electrons from the mirror surface and accelerates them toward the geometric focus, where the intensity reaches a0 ≈ 4000, triggering an avalanche-type cascade with more than seven generations. The generated pairs are accelerated within a propagating wave rather than a standing wave, producing 60 nC of pairs in collimated beams with high contrast to background electrons. The generated pair plasma exhibits collective behavior, absorbing the incident laser power and screening the laser field at high intensities. This single-beam geometry eliminates multipulse alignment requirements and provides a direct path to studying prolific light-to-matter conversion in strong-field QED.
X-ray phase-contrast imaging (XPCI) provides superior sensitivity for the diagnosis of low-Z materials compared with absorption-based techniques. Betatron radiation generated by laser wakefield accelerators, which offers high photon flux, ultra-short duration, and relatively high spatial coherence, is a promising compact source for XPCI. At present, there is a lack of knowledge about how to control wakefield accelerators and realize high-quality XPCI. This study investigates the influence of gas pressure (plasma density) on betatron source characteristics and on the performance of propagation-based XPCI. Through particle-in-cell and wave-optics simulations, it explores the relationship between gas pressure and imaging characteristics such as spatial resolution and brightness and determines an optimal operation window. Experimental results confirm this optimal operation window at 40–45 psi [plasma density ∼3–4×1018cm−3], with which a peak photon flux of 8×1012photons/sr and a contrast of 20.32% at a spatial resolution of 5 μm are realized. This study demonstrates a pathway for the optimization of betatron-based XPCI, enabling synchrotron-comparable spatial resolution in a laboratory-scale setup and shows the potential of XPCI in ultrafast microscopic imaging applications.
Collective Thomson scattering (CTS) is crucial for inertial confinement fusion (ICF) hohlraum diagnostics, but measurement of the electron plasma wave (EPW) feature remains challenging. The conventional collisionless model suffers from two critical defects: under low-temperature, high-density conditions it predicts an extremely narrow EPW peak that causes numerical sampling distortion, and it predicts a monotonic increase of peak intensity with decreasing scattering angle, which would mislead experimental design. To overcome these issues, the Bhatnagar–Gross–Krook (BGK) collisional model is introduced. The BGK model predicts a nonmonotonic peak intensity with an optimal angle between 30° and 60°, and yields a finite, resolvable peak width that eliminates sampling artifacts. It also enables reliable assessment of drive-beam backgrounds. Guided by the predicted optimal angle, CTS experiments at 42° were performed on the Shenguang-100 kJ facility. For the first time, both ion and electron features were simultaneously measured in the hohlraum corona, with the electron signal clearly distinguishable from the background. Joint fitting provides the temporal evolution of electron density and temperature. This work establishes a unified, collision-corrected diagnostic framework that overcomes a long-standing obstacle to measuring electron density and temperature in ICF hohlraum plasmas.
In 2017, Dias and Silvera [Science 355, 715–718 (2017)] claimed the first laboratory observation of the Wigner–Huntington transition of hydrogen to its metallic phase at 495 GPa. Because this claim relies critically on optical diagnostics and pressure calibration under extreme conditions, reproducibility and full traceability of the underlying datasets are essential. Here, we re-examine the raw data files released alongside the publication. We identify (i) nonuniform intervals of data points in the released diamond Raman spectrum, consistent with artificial removal or adjustment of data points without corresponding disclosure; (ii) pronounced mismatches between the released infrared transmission spectra and the curves shown in the published supplementary materials; and (iii) a highly limited and editable reflectance dataset that is insufficient for independent verification of the reflectivity-based metallicity claim. These issues not only prevent independent reconstruction of key figures, but also cast doubt on the authenticity of Dias and Silvera’s research findings. We encourage clarification of the provenance of the released files and the provision of complete raw datasets and processing details to enable community-wide verification.
Ultrafast, high-power lasers operating in the near-infrared (NIR) region are key to accelerating ions to extremely high energies. By changing the laser wavelength from the NIR region to the hard X-ray range, the photon energy increases more than 10000 times. The interaction mechanisms and, consequently, radiation attenuation lengths differ significantly between these two spectral ranges. Here we report the use of an X-ray free-electron laser (European XFEL, Germany) delivering 9.3 keV photons in 25 fs pulses and a total energy of 0.35 ml on a solid target. Electrons and ions escaping from an irradiated 3 & micro;m Cu foil into vacuum were investigated by a time-of-flight technique using windowless electron multipliers that enable the measurement of very weak currents. A model based on a shifted Maxwell-Boltzmann velocity distribution of species was used to analyze the detector signals. The method used made it possible to determine the temperatures of hot electrons and protons, their center-of-mass energy, the charge states of the isotopes Cu-63 and Cu-65, and the magnitude of the voltage arising in the double layer that accelerated them, and to estimate the repetition frequency of their cascade emission from the plasma. Computer simulations revealed the evolution of the electron density and temperature, the ion charge state distribution, and the time scales of processes occurring in the bulk of irradiated matter. Good correlation of theoretical and experimental results over the range of high-energy-density states demonstrates the capability to provide critical data to develop plasma models in the warm dense matter regime.
Achieving diffraction-limited focusing of high-power laser pulses to generate ultrahigh intensities is crucial for developing compact laser-driven particle accelerators and exploring strong-field quantum electrodynamics. However, accurately diagnosing and optimizing the focal spots of petawatt (PW) laser pulses remains a significant challenge. In this work, we present an experimental methodology utilizing a twin-focus scheme to precisely characterize the intensity distribution and wavefront of focused PW femtosecond laser pulses, and employ it to elucidate their power-dependent evolution. Furthermore, we optimize the focal spots at full power via our in situ wavefront correction method called “HotLoop,” achieving a Strehl ratio of 0.80 for 1 PW laser pulses. Consequently, the cutoff proton energies in laser proton acceleration experiments are significantly enhanced. The success of this approach underscores the necessity of in situ high-energy wavefront correction for ultrahigh-intensity laser–matter interactions.
The Langmuir decay instability (LDI) is a key saturation mechanism for stimulated Raman scattering (SRS) in inertial confinement fusion plasmas. However, a quantitative characterization of the two-dimensional angular spectrum of LDI in such inhomogeneous environments, particularly its dependence on the pump-wave incidence angle, remains limited. Here, we combine a k-space theoretical model with two-dimensional particle-in-cell simulations to study a localized Langmuir wave packet in a linear density gradient. Our results show that although the density gradient suppresses the overall strength of LDI, the backscattering channel (φ ≈ 180°) remains the dominant decay mode across all tested pump incidence angles. These results help clarify the multidimensional evolution of LDI in inhomogeneous plasmas and may be useful for developing more predictive models of SRS saturation in laser-fusion schemes.
Transition metal phosphides exhibit diverse crystal structures and intriguing physical properties, including superconductivity and magnetism. Despite extensive studies, obtaining a comprehensive understanding of the synthesis methods, structural variations, and emergent phenomena in binary and ternary phosphides remains an essential task. Here, we review recent progress in the synthesis, crystal structures, and physical properties of binary (e.g., Mo–P, Rh–P, Re–P, and Ir–P) and ternary (transition metal–transition metal–phosphorus, alkaline earth metal–transition metal–phosphorus, and rare earth element–transition metal–phosphorus) phosphides. Emphasis is placed on superconductivity, magnetism, and electronic structures, highlighting correlations between composition, structure, and properties. This synthesis of current knowledge provides insights into the design of novel phosphide materials and can guide future exploration of functional materials with tailored electronic and magnetic behaviors.
For decades, γ-N2 has been known to exist at very low temperatures and pressures, located in a tiny area of the nitrogen phase diagram. Recently, it was shown that γ-N2 occupies most of the P–T space usually associated with molecular phases such as δ, ɛ, and ζ, and that it plays a pivotal role in shaping nitrogen’s phase diagram. Using powder synchrotron X-ray diffraction, Raman and infrared spectroscopy, and density function theory calculations, we have investigated the structural and optical properties of γ-N2 in a wide P–T range. The combined X-ray diffraction and infrared spectroscopy results unequivocally demonstrate that γ-N2 adopts the monoclinic (P21/c space group) configuration with two N2 molecules per unit cell. It appears that the γ-N2 is structurally closely related to θ-N2, leading to both phases having very similar Raman signatures. Additionally, the Raman spectroscopy reveals a vibrational mode intensity resonance effect in both phases, caused by a strong vibrational coupling between the isotopic 15N14N and 14N2 vibrational excitations.
High-energy, high-yield structured spin-polarized positron beams have important applications in nuclear physics, high-energy physics, and information storage. However, their generation remains a significant challenge. Here, we put forward a scheme to generate these beams using a dense relativistic electron beam interacting with a gas-filled cone–channel target. The interaction induces composite focusing fields comprising the electric field from a plasma bubble and skin-layer magnetic fields from the electron beam and displacement currents. These fields compress the seed beam to ultrahigh density, thereby inducing extreme fields that enable efficient γ-photon emission and subsequent pair production, leading to a high positron yield. Furthermore, the azimuthal topology of these fields is imprinted onto the generated positrons, creating unique azimuthal polarization. Our simulations demonstrate the generation of an azimuthally polarized positron beam with a charge of 0.63 nC, a polarization approaching 60%, and an energy conversion efficiency exceeding 3%. Our method provides a highly efficient pathway for generating azimuthally polarized positrons, paving the way for their potential applications.
Porous materials have particular advantages for a variety of applications in inertial confinement fusion. To identify suitable new materials for these applications, it is important to investigate their interaction with high-power lasers and the associated plasma evolution. In this work, we report on the results of an experimental campaign performed at the ABC laser facility, employing carefully characterized nanostructured carbon foams obtained with the pulsed laser deposition technique. The enhancement of the ablation loading due to the foam buffer is evaluated by comparing the volume of the crater left after the interaction among different samples. Particular foam parameters and morphology are found to increase the ablation loading by producing a larger crater volume. Visible side-on streak camera images confirm these results. The absorption efficiency is investigated by time-resolved measurement of the laser light collected by focusing lenses and acquired by two fast photodiodes.
Iodide ions can form crystal lattices with large interstitial spaces, making them archetypal systems for investigating superionic phase transitions. Understanding how iodine-based lattices evolve under different thermodynamic conditions is therefore a central problem in condensed matter physics and functional materials design. Aluminum iodide (AlI3) is a molecular solid crystal with low ionic conductivity under ambient conditions, and it plays important roles in batteries and catalytic applications, motivating exploration of its pressure-tunable ionic transport behavior. Here, we reveal the pressure-induced structural dimensionality evolution in AlI3 through first-principles structural searches and synchrotron X-ray diffraction (XRD). We identify a sequence of phase transitions: from the molecular P21/c phase to a two-dimensional layered rhombohedral (R-3) phase above 1.3 GPa, and subsequently to a one-dimensional chain-like orthorhombic (Cmcm) phase beyond 49 GPa. Notably, in situ laser-heating XRD and ab initio molecular dynamics simulations reveal that the R-3 phase undergoes a transition to a superionic state at high temperatures, where Al3+ ions undergo partially disordered, rapid diffusion within the rigid iodine layers. We further demonstrate that the introduction of Al3+ vacancies substantially reduces the superionic transition temperature. Our work not only maps the structural evolution of AlI3 under pressure, but also provides a key reference for the structural design of metal halides under high pressure.
For moderately/strongly coupled plasmas, modeling of the electron screening effect remains an unresolved problem, owing to the complicated many-body correlations among the surrounding electrons and ions. In this work, we investigate the ion correlation effect on electron screening of moderately coupled plasmas using an atomic-state-dependent electron-screening model. It is found that the electron density around a target ion is significantly enhanced by the ion correlation effect from surrounding ions. By considering this ion correlation effect, the electron density fluctuation induced by the target ion becomes non-spherically symmetric, which causes traditional electron screening models to underestimate the screening effects, especially for moderately/strongly coupled and weakly degenerate plasmas. The present model and findings are validated by molecular dynamics simulations of moderately coupled ultracold neutral plasmas. For moderately coupled plasmas, the Coulomb logarithm is found to decrease by about 10%–30% owing to the ion correlation effect, which should be considered when modeling plasma effects on atomic processes, radiation transport, and thermodynamic properties.
We propose and elaborate a novel analytical method for describing the fundamental scattering processes of ultrashort laser pulses in matter under extreme conditions using the total scattering coefficient. This method considers the specifics of ultrafast electromagnetic interaction and the effects of pulse propagation in dense matter. It is demonstrated that analytical expressions can be obtained within the framework of the local plasma frequency model, allowing a link to be established between the dynamic polarizability and the dressed ion sphere that represents the extremely dense matter. Extinction and scattering cross sections are then functionals of the electron density, which is calculated in a self-consistent quantum-mechanical approach. Detailed calculations are carried out for the Al12+ ion in near-solid-density plasmas. The dependences on the laser pulse parameters and the opacity of the plasma are analyzed. Specific features of these dependences are established and explained.
