Damage to compression gratings poses a fundamental limit to chirped pulse amplification in high-power laser systems. Plasma-based compressors using strongly coupled stimulated Brillouin scattering (scSBS) offer a damage-free alternative, but their effectiveness has been hindered by instabilities that constrain interaction length. In this study, we report the first experimental demonstration of scSBS amplification driven by a flying focus in a 3 mm plasma channel. The flying focus is generated using chromatic aberration from spherical lenses, with its velocity precisely measured by an interferometric ionization method achieving 6.6 fs timing resolution. At a focus velocity near −c, scSBS amplification is realized at pump and seed intensities more than two orders of magnitude lower than in conventional schemes, yielding a conversion efficiency of 14.5%. The result is also supported by two-dimensional particle-in-cell simulations. These results demonstrate the effectiveness of flying focus as a tool for extending interaction lengths and enabling efficient plasma-based laser amplification at reduced intensities.
Electronic entropy is usually treated as a secondary correction to structural stability, but under strong electronic excitation it can become a primary thermodynamic driving force. Here, we show that electronic entropy can drive both polymorphic and stoichiometric phase transformations in compressed iron oxides. Using finite-temperature density functional theory, we calculate the electronic-temperature-dependent Gibbs free energies of Fe2O, FeO, Fe4O5, Fe3O4, and multiple Fe2O3 polymorphs, including α-, ι-, ζ-, η-, and θ-Fe2O3, over the pressure range 60–260 GPa. At 60–140 GPa, electronic excitation mainly reorganizes the relative stability of Fe2O3 polymorphs, driving transitions from ι-Fe2O3 to η-Fe2O3. At 180 GPa, the free-energy landscape becomes strongly competitive as FeO is stabilized over an intermediate range of electronic temperature, while η-Fe2O3 becomes favorable at higher T. At 220–260 GPa, the lowest-free-energy phase at low T is the Fe-rich compound Fe2O, but increasing electronic temperature stabilizes FeO. These results demonstrate that electronic entropy can control not only the relative stability of crystal structures at fixed composition, but also the competition between different iron-oxide stoichiometries. The predicted electronic-entropy-driven phase boundaries provide a route to nonthermal structural transformations in ultrafast and high-energy-density experiments.
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.
