A scaling study of short-pulse laser-driven proton and electron acceleration was conducted as a function of pulse duration, laser energy, and laser intensity in the multi-picosecond (ps) regime (∼0.8 ps–20 ps). Maximum proton energies significantly greater than established scaling laws were observed, consistent with observations at other multi-ps laser facilities. In addition, maximum proton energies and electron temperatures in this regime were found to be strongly dependent on the laser pulse duration and preplasma conditions. A modified proton scaling model is presented that is able to better represent the accelerated proton characteristics in this multi-ps regime.

While silicon carbide (SiC) has been predicted to undergo pressure-induced amorphization, the micro structural evidence of such a drastic phase change is absent as its brittleness usually prevents its successful recovery from high-pressure experiments. Here we report on the observation of amorphous SiC recovered from laser-ablation-driven shock compression with a peak stress of approximately 50 GPa. Transmission electron microscopy reveals that the amorphous regions are extremely localized, forming bands as narrow as a few nanometers. In addition to these amorphous bands, planar stacking faults are observed. Large-scale non-equilibrium molecular dynamic simulations elucidate the process and suggest that the planar stacking faults serve as the precursors to amorphization. Our results suggest that the amorphous phase produced is a high-density form, which enhances its thermodynamical stability under the high pressures combined with the shear stresses generated by the uniaxial strain state in shock compression. (C) 2018 Published by Elsevier Ltd on behalf of Acta Materialia Inc.

A set of experiments has been performed exploring unique characteristics of pair jets and plasmas at several energetic short-pulse laser facilities including Titan at Livermore and OMEGA EP in Rochester, as well as the Osaka LFEX and AWE Orion lasers. New results are summarized, including positron beam emittance, scaling of pair production vs. laser energy, and initial results on the pair jet collimation using electromagnetic fields.

The field of strongly coupled Coulomb systems that stretches from dense plasma, to astrophysics, condensed matter and high energy physics has seen a dramatic development over the last four decades. At the beginning of this process were a few physicists whose work has had a high impact on many exciting developments of the recent years. Among them are Hugh E. DeWitt, Bernard Jancovici and Forrest J. Rogers who passed away in 2013-2014. Their important contributions to the field of strongly coupled Coulomb systems are summarized in this article. (C) 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

Indirect laser-driven shockless compression experiments on gold targets were performed to characterize pressure loading processes and target states. Free surface velocities of the gold target under ramped pressure loading were measured using line-imaging velocity interferometers. From the velocity data and the equation of state, the maximum pressure and strain rate attained under compression were estimated to be ∼50 GPa and ∼4 × 107 s−1, respectively. Optical reflectivity was measured simultaneously with the velocity, the result suggesting no significant or unexpected temperature increases in the ultrafast shockless compression process.

We review recent experimental results on the path to producing electron-positron pair plasmas using lasers. Relativistic pair-plasmas and jets are believed to exist in many astrophysical objects and are often invoked to explain energetic phenomena related to Gamma Ray Bursts and Black Holes. On earth, positrons from radioactive isotopes or accelerators are used extensively at low energies (sub-MeV) in areas related to surface science positron emission tomography and basic antimatter science. Experimental platforms capable of producing the high-temperature pair-plasma and high-flux jets required to simulate astrophysical positron conditions have so far been absent. In the past few years, we performed extensive experiments generating positrons with intense lasers where we found that relativistic electron and positron jets are produced by irradiating a solid gold target with an intense picosecond laser pulse. The positron temperatures in directions parallel and transverse to the beam both exceeded 0.5 MeV, and the density of electrons and positrons in these jets are of order 10(16) cm(-3) and 10(13) cm(-3), respectively. With the increasing performance of high-energy ultra-short laser pulses, we expect that a high-density, up to 10(18) cm(-3), relativistic pair-plasma is achievable, a novel regime of laboratory-produced hot dense matter. (C) 2011 Elsevier B.V. All rights reserved.

High power lasers are a tool that can be used to determine important parameters in the context of Warm Dense Matter, i.e. at the convergence of low-temperature plasma physics and finite-temperature condensed matter physics. Recent results concerning planet inner core materials such as water and iron are presented. We determined the equation of state, temperature and index of refraction of water for pressures up to 7 Mbar. The release state of iron in a LiF window allowed us to investigate the melting temperature near the inner core boundary conditions. Finally, the first application of proton radiography to the study of shocked material is also discussed.

An accurate equation of state (EOS) for planetary constituents at extreme conditions is the key to any credible model of planets or low mass stars. However, very few materials have their high pressure (>few Mbar) EOS experimentally validated, and even then, only on the principal Hugoniot. For planetary and stellar interiors, compression occurs from gravitational force so that material states follow a line of isotropic compression (ignoring phase separation) to ultra-high densities. An example of the hydrogen phase space composing Jupiter and one particular Brown Dwarf is shown. At extreme densities, material states are predicted to have quite unearthly properties such as high temperature superconductivity and low temperature fusion. High density experiments on Earth are achieved with either static compression techniques (i.e. diamond anvil cells) or dynamic compression techniques using large laser facilities, gas guns, or explosives. The ultimate goal of this multi-directorate and multi-institutional proposal was to develop techniques that will enable us to understand material states that previously only existed at the core of giant planets, stars, or speculative theories. Our effort was a complete success, meeting all of the objectives set out in our proposals. First we focused on developing accurate Hugoniot techniques to be used for constraining the equation of state at high pressure/temperature. We mapped out an accurate water EOS and measured that the ionic->electronic conduction transition occurs at lower pressures than models predict. These data and their impact are fully described in the first enclosed paper ''The Equation of State and Optical Properties of Water Compressed by Strong Shock Waves.'' Currently models used to construct planetary isentropes are constrained by only the planet radius, outer atmospheric spectroscopy, and space probe gravitational moment and magnetic field data. Thus these data, which provide rigid constraints to these models, will have a significant impact on a broad community of planetary and condensed matter scientists, as well as our fundamental understanding of the giant planets. We then developed and tested precompressed and multiple shock techniques on water. Scientists around the world have teamed with us to conduct these complex and seminal high density experiments which allow access to the extreme core states of giant plants. Double shock experiments using a variety of anvils to compress water to densities higher and temperatures lower than accessible by single shock Hugoniot techniques. First a clear determination of the EOS and optical properties of the anvils needed to be measured. These properties for LiF and A1203 are written up in the second attached article, ''Shock-Induced Transformation of Sapphire and Lithium Fluoride into Semiconducting Liquids.'' An example double shock data record for water is shown. This data is being written up for publication.

We present equation of state points for iron, in the pressure range 10-45 Mbar, the first obtained with laser-driven shock waves. The experiment has been performed with the high energy laser Phebus, optically smoothed with Kinoform phase plates. Our results double the set of existing experimental data at very high pressures showing good agreement with the predictions of the quotidian equation of state model and with previous results.

Isentropic compression experiments that utilize intense magnetic fields to compress samples have been designed, developed and performed. The technique has been shown to work to pressures of more than 1 Mbar on Sandia National Laboratory's Z pulsed power machine. We are extending the technique to use high-explosive pulsed power.

Four larval ticks belonging to the genus Amblyomma (Acari: Ixodidae), and so far as we are able to discern, all belonging to the same species, were found in Dominican Republic amber deposits. These specimens represent the second known collection of an Amblyomma species in amber, and the first fossil larva of the hard tick family Ixodidae. These larval Amblyomma species most closely resemble A. dissimile, an amphibian and reptilian ectoparasite found in the southern United States through the Caribbean, Central America and South America. This is also the first report in which a series of fossil ticks has been described. Because we were unable to see dorsal body setae on these larval Amblyomma specimens, we can neither unconditionally state that they are A. dissimile, nor constitute a new species of the genus Amblyomma.