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Accurate knowledge of the electronic transport properties of warm dense matter is one of the main concerns of research in high-energy-density physics. Three modern approaches with vastly different levels of fidelity are reviewed and compared: the Kubo–Greenwood (KG) approach based on density-functional-theory molecular dynamics simulations (QMD), quantum kinetic theory based on average-atom models, and time-dependent density functional theory. Throughout, emphasis is placed on the connection between static properties of the electrons (e.g., density of states) and transport properties. Overall, it is found that whenever the conduction electrons can be modeled as being nearly free, fair to excellent agreement is found between QMD and kinetic theory approaches. Such a circumstance is required for modeling warm dense matter as a plasma of ions and free electrons, which is assumed in most kinetic theory approaches. The sensitivity of transport properties to the electronic structure is further highlighted by comparing different exchange–correlation approximations in QMD and KG calculations. It is found that the inclusion of exact exchange via thermal hybrid functionals can make a pronounced impact on electrical and thermal conduction in warm dense matter. We also investigate dynamic screening physics via kinetic theory and time-dependent density functional theory calculations of the mean free path of an electron in a hot dense plasma. In sum, we identify three axes along which to make progress in predicting electron transport in warm dense matter. [ABSTRACT FROM AUTHOR]

Inertial confinement fusion (ICF) with the laser-indirect-drive scheme has recently made a tremendous breakthrough recently after decades of intensive research effort. Taking this success to the next step, the ICF community is coming to a general consensus that laser direct-drive (LDD) fusion might be the viable way for enabling inertial fusion energy (IFE) and high-gain targets for other applications. Designing and understanding LDD fusion targets heavily rely on radiation-hydrodynamic code simulations, in which charged-particle transport plays an essential role in modeling laser-target energy coupling and bootstrap heating of fusion-produced α-particles. To better simulate charged-particle transport in LDD targets, over the past four decades the plasma physics community has advanced transport calculations from simple plasma physics models to sophisticated computations based on first-principles methods. In this review, we give an overview of the current status of charged-particle transport modeling for LDD fusion, including what challenges we still face and the possible paths moving forward to advance transport modeling for ICF simulations. We hope this review will provide a summary of exciting challenges to stimulate young minds to enter the field, facilitate further progress in understanding warm-dense matter physics, and ultimately bridge toward the success of reliable LDD fusion designs for IFE and other high-gain ICF applications. [ABSTRACT FROM AUTHOR]

We have demonstrated generation and transport of a patterned electron beam from a Diamond Field-Emitter Array (DFEA) cathode in a radio frequency (rf) gun. DFEAs are arrays of micrometer-scale pyramids with nanometer-scale tips. They can be fabricated with base widths ranging from 3 μm to 25 μm and pitches as small as 5 μm. They have an inherent 1:0.7 base to height ratio. DFEAs operate as field-emitter cathodes and potentially produce intrinsically shaped electron beams, which are of interest for a number of accelerator applications. We report on the results of a recent experiment in which a beam, consisting of several beamlets, was produced from a DFEA cathode in an rf gun and transported 2.54 m along a beam line. A macrobunch charge of 60 pC was measured at a cathode field gradient of 15.1 MV/m. [ABSTRACT FROM AUTHOR]

We describe the fabrication and performance of the first spatial light modulators (SLM’s) which combine addressing in AlGaAs charge-coupled devices (CCD’s) and electroabsorption effects in GaAs/AlGaAs multiple quantum wells (MQW’s). One-dimensional, sixteen-stage, three-phase AlGaAs CCD’s with semitransparent gates were fabricated on the surface of the SLM. The optical signal propagates normal to the surface and enters the SLM through the gates. The transmission of this signal through the MQW is then modulated according to the channel voltage of the CCD’s. The maximum contrast ratio at 847 nm was measured to be 1.45:1 for these GaAs/AlGaAs -based SLM’s. [ABSTRACT FROM AUTHOR]

Resonant slot and dipole antennas coupled to low-temperature-grown GaAs photomixers have been fabricated and tested at terahertz operating frequencies. Enhanced output power is seen from the resonant structures compared to mixers coupled to broadband self-complementary spiral antennas. Driving point impedances as high as 300 Ω are attained at the resonant frequencies. These devices will be useful as fixed frequency local oscillators for submillimeter heterodyne receivers. © 1996 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Nondegenerate four-wave mixing experiments have been conducted in Al0.2Ga0.8As ridge waveguides, using picosecond laser pulses. Maker fringes due to phase-matching requirements were clearly observed, and phase-matched nondegenerate mixing was achieved by utilizing the waveguide geometrical birefringence. Conversion efficiency up to 5×10-3 for a coherent interaction length of 3 mm was obtained. The observed third-order nonlinear susceptibility χ(3)(ω3=ω1+ω1-ω2) does not display any strong resonances and exhibits a relaxation time shorter than 10 ps. From these measurements it is inferred that |χ(3)1111|≥8×10-11 esu, and |χ(3)1111/χ(3)2112|=2.4±0.3 for ω1 and ω2≊1480 meV/h. [ABSTRACT FROM AUTHOR]

A guided-wave interferometer capable of modulating 1.3-μm radiation via the electro-optic effect has been fabricated in GaAs. The interferometer uses three-guide couplers as the input and output sections and single-mode slab-coupled p+-n--n+ rib waveguides fabricated by means of Be-ion implantation for the two active arms. An extinction of ≊14.5 dB of the output signal from the center guide is obtained with 22 V applied to one arm of the interferometer. Interferometers of this type should be capable of large signal modulation out to 5-10 GHz. [ABSTRACT FROM AUTHOR]