Efficiency enhancement for Kα x-ray yields from laser-driven relativistic electrons in solids

Two-dimensional monitoring of a laser-solid x-ray source spot via penumbral coded aperture imaging technique

The uncertainties of spot size and position need to be clarified for x-ray sources as they can affect the detecting precision of the x-ray probe beam in applications such as radiography. In particular, for laser-driven x-ray sources, they would be more significant as they influence the inevitable fluctuation of the driving laser pulses. Here, we have employed the penumberal coded aperture imaging technique to diagnose the two-dimensional spatial distribution of an x-ray emission source spot generated from a Cu solid target irradiated by an intense laser pulse. Taking advantage of the high detection efficiency and high spatial resolution of this technique, the x-ray source spot is characterized with a relative error of ∼5% in the full width at half maximum of the intensity profile in a single-shot mode for general laser parameters, which makes it possible to reveal the information of the unfixed spot size and position precisely. Our results show the necessity and feasibility of monitoring the spot of these novel laser-driven x-ray sources via the penumbral coded aperture imaging technique.

Exploring Whether Data Can be Represented as a Composite Unit in Form Processing Using the Manufacturing of Information Approach

Data and information quality have been recognized as essential components for improving business efficiency. One approach for the assessment of information quality (IQ) is the manufacturing of information (MI). So far, research using this approach has considered a whole document as one indivisible block, which allows document evaluation only at a general level. However, the data inside the documents can be represented as components, which can further be classified according to content and composition. In this paper, we propose a novel model to explore the effectiveness of representing data as a composite unit, rather than indivisible blocks. The input data sufficiency and the relevance of the information output are evaluated in the example of analyzing an administrative form. We found that the new streamlined form proposed resulted in a 15% improvement in IQ. Additionally, we found the relationship between the data quantity and IQ was not a “simple” correlation, as IQ may increase without a corresponding increase in data quantity. We conclude that our study shows that the representation of data as a composite unit is a determining factor in IQ assessment.

Energy transfer dynamics in strongly inhomogeneous hot-dense-matter systems

Direct measurements of energy transfer across steep density and temperature gradients in a hot-dense-matter system are presented. Hot-dense-plasma conditions were generated by high-intensity laser irradiation of a thin-foil target containing a buried metal layer. Energy transfer to the layer was measured using picosecond time-resolved x-ray emission spectroscopy. The data show two x-ray flashes in time. Fully explicit, coupled particle-in-cell and collisional-radiative atomic kinetics model predictions reproduce these observations, connecting the two x-ray flashes with staged radial energy transfer within the target.

Laser-plasmas in the relativistic-transparency regime: Science and applications

Laser-plasma interactions in the novel regime of relativistically induced transparency (RIT) have been harnessed to generate intense ion beams efficiently with average energies exceeding 10 MeV/nucleon (>100 MeV for protons) at "table-top" scales in experiments at the LANL Trident Laser. By further optimization of the laser and target, the RIT regime has been extended into a self-organized plasma mode. This mode yields an ion beam with much narrower energy spread while maintaining high ion energy and conversion efficiency. This mode involves self-generation of persistent high magnetic fields (∼10⁴ T, according to particle-in-cell simulations of the experiments) at the rear-side of the plasma. These magnetic fields trap the laser-heated multi-MeV electrons, which generate a high localized electrostatic field (∼0.1 T V/m). After the laser exits the plasma, this electric field acts on a highly structured ion-beam distribution in phase space to reduce the energy spread, thus separating acceleration and energy-spread reduction. Thus, ion beams with narrow energy peaks at up to 18 MeV/nucleon are generated reproducibly with high efficiency (≈5%). The experimental demonstration has been done with 0.12 PW, high-contrast, 0.6 ps Gaussian 1.053 μm laser pulses irradiating planar foils up to 250 nm thick at 2-8 × 10²⁰ W/cm². These ion beams with co-propagating electrons have been used on Trident for uniform volumetric isochoric heating to generate and study warm-dense matter at high densities. These beam plasmas have been directed also at a thick Ta disk to generate a directed, intense point-like Bremsstrahlung source of photons peaked at ∼2 MeV and used it for point projection radiography of thick high density objects. In addition, prior work on the intense neutron beam driven by an intense deuterium beam generated in the RIT regime has been extended. Neutron spectral control by means of a flexible converter-disk design has been demonstrated, and the neutron beam has been used for point-projection imaging of thick objects. The plans and prospects for further improvements and applications are also discussed.

Energy penetration into arrays of aligned nanowires irradiated with relativistic intensities: Scaling to terabar pressures

Ultrahigh-energy density (UHED) matter, characterized by energy densities >1 × 10⁸ J cm^-3 and pressures greater than a gigabar, is encountered in the center of stars and inertial confinement fusion capsules driven by the world's largest lasers. Similar conditions can be obtained with compact, ultrahigh contrast, femtosecond lasers focused to relativistic intensities onto targets composed of aligned nanowire arrays. We report the measurement of the key physical process in determining the energy density deposited in high-aspect-ratio nanowire array plasmas: the energy penetration. By monitoring the x-ray emission from buried Co tracer segments in Ni nanowire arrays irradiated at an intensity of 4 × 10¹⁹ W cm^-2, we demonstrate energy penetration depths of several micrometers, leading to UHED plasmas of that size. Relativistic three-dimensional particle-in-cell simulations, validated by these measurements, predict that irradiation of nanostructures at intensities of >1 × 10²² W cm^-2 will lead to a virtually unexplored extreme UHED plasma regime characterized by energy densities in excess of 8 × 10¹⁰ J cm^-3, equivalent to a pressure of 0.35 Tbar.