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We present the chemical bonding and electronic properties of liquid methane at temperatures from 2000 to 4000 K and high densities of up to 3.0 g/cm3, calculated using ab initio molecular dynamics simulations in combination with the Mulliken population analysis. Bond-overlap populations and pair distribution functions are studied to investigate the evolution of electron delocalization accompanying atomic structure change as the density is increased. In addition, we also investigated the bandgap energy, electronic density of states, and spatial distribution of electron density. We observed that molecular hydrogen and C‒C bonds are formed after methane dissociates, and then the system undergoes a nonmetal–metal transition coinciding with hydrogen being transformed from the molecular to the atomic state. The C‒C bonds in the system retain covalent character, even at the highest density of 3.0 g/cm3. [ABSTRACT FROM AUTHOR]

When a laser is focused on an underwater object, it experiences a large amount of pressure owing to the plasma confinement effect of water. A hemispherical bubble is generated on the surface of the object, and large pressure is generated when the bubble collapses. In this study, we conducted experiments using different laser energies to analyze the pressure–time histories associated with bubble contraction. The maximum pressure was 10%–40% of the laser ablation pressure, whereas the pressure pulse width was 5–10 times longer than the laser pulse width. Furthermore, the bubble motion could be adiabatically explained, except for the plasma interaction region. The results indicate that the pressure at which the bubble collapses does not depend on the maximum size of the generated bubble but depends on the energy of water vapor within the bubble. [ABSTRACT FROM AUTHOR]

Ultrahigh-energy density (UHED) states greater than 1 Gbar pressure are typically observed under extreme conditions, such as in the core of an inertial confinement fusion implosion. A novel alternative approach for generating volumetric UHED states is to use nanowire arrays irradiated with a femtosecond ultrahigh-intensity laser. In this paper, we present an experimental investigation on laser absorption and energy transport in nanowire arrays irradiated with a picosecond kilojoule petawatt laser. The laser–target interactions were studied by measuring the x-ray emission and escaping hot electrons from a bare Cu foil and a foil with a nanowire array grown on its surface. The measured Cu-Kα and He-α emissions from the nanowire array were higher than those from the flat foil. In addition, hot electrons observed from the front surface of the nanowire array were enhanced. On the other hand, despite the stronger Kα emission from the nanowire array and the enhancement of hot electrons escaping from the front surface of the nanowire array, the number of hot electrons observed from the rear side of the flat foil target was slightly lower than that of the flat foil. A comparison of the experimental results with the results of a two-dimensional particle-in-cell simulation code suggested that the magnetic fields generated around the periodic nanowire array trap hot electrons, improving the electron-to-target energy coupling and efficiently producing UHED states. [ABSTRACT FROM AUTHOR]

The shock ignition (SI) approach to inertial confinement fusion is a promising scheme for achieving energy production by nuclear fusion. SI relies on using a high intensity laser pulse (≈1016 W/cm2, with a duration of several hundred ps) at the end of the fuel compression stage. However, during laser–plasma interaction (LPI), several parametric instabilities, such as stimulated Raman scattering and two plasmon decay, nonlinearly generate hot electrons (HEs). The whole behavior of HE under SI conditions, including their generation, transport, and final absorption, is still unclear and needs further experimental investigation. This paper focuses on the development of an experimental platform for SI-related experiments, which simultaneously makes use of multiple diagnostics to characterize LPI and HE generation, transport, and energy deposition. Such diagnostics include optical spectrometers, streaked optical shadowgraph, an x-ray pinhole camera, a two-dimensional x-ray imager, a Cu Kα line spectrometer, two hot-electron spectrometers, a hard x-ray (bremsstrahlung) detector, and a streaked optical pyrometer. Diagnostics successfully operated simultaneously in single-shot mode, revealing the features of HEs under SI-relevant conditions. [ABSTRACT FROM AUTHOR]

The interaction between a molecular cloud and an external agent (e.g., a supernova remnant, plasma jet, radiation, or another cloud) is a common phenomenon throughout the Universe and can significantly change the star formation rate within a galaxy. This process leads to fragmentation of the cloud and to its subsequent compression and can, eventually, initiate the gravitational collapse of a stable molecular cloud. It is, however, difficult to study such systems in detail using conventional techniques (numerical simulations and astronomical observations), since complex interactions of flows occur. In this paper, we experimentally investigate the compression of a foam ball by Taylor–Sedov blast waves, as an analog of supernova remnants interacting with a molecular cloud. The formation of a compression wave is observed in the foam ball, indicating the importance of such experiments for understanding how star formation is triggered by external agents. [ABSTRACT FROM AUTHOR]

We present an indirect method of estimating the strength of a shock wave, allowing on line monitoring of its reproducibility in each laser shot. This method is based on a shot-to-shot measurement of the X-ray emission from the ablated plasma by a high resolution, spatially resolved focusing spectrometer. An optical pump laser with energy of 1.0 J and pulse duration of ∼660 ps was used to irradiate solid targets or foils with various thicknesses containing Oxygen, Aluminum, Iron, and Tantalum. The high sensitivity and resolving power of the X-ray spectrometer allowed spectra to be obtained on each laser shot and to control fluctuations of the spectral intensity emitted by different plasmas with an accuracy of ∼2%, implying an accuracy in the derived electron plasma temperature of 5%-10% in pump-probe high energy density science experiments. At nano- and sub-nanosecond duration of laser pulse with relatively low laser intensities and ratio Z/A∼0.5, the electron temperature follows Te∼Ilas2/3. Thus, measurements of the electron plasma temperature allow indirect estimation of the laser flux on the target and control its shot-to-shot fluctuation. Knowing the laser flux intensity and its fluctuation gives us the possibility of monitoring shot-to-shot reproducibility of shock wave strength generation with high accuracy. [ABSTRACT FROM AUTHOR]

Pressure, density, and temperature data for H2O were obtained up to 260 GPa by using laser-driven shock compression technique. The shock compression technique combined with the diamond anvil cell was used to assess the equation of state models for the P-ρ-T conditions for both the principal Hugoniot and the off-Hugoniot states. The contrast between the models allowed for a clear assessment of the equation of state models. Our P-ρ-T data totally agree with those of the model based on quantum molecular dynamics calculations. These facts indicate that this model is adopted as the standard for modeling interior structures of Neptune, Uranus, and exoplanets in the liquid phase in the multi-Mbar range. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Astronomical observations reveal that the interaction between shock waves and/or blast waves with astrophysical objects (molecular clouds, stars, jet winds, etc.) is a common process which leads to a more intricate structure of the interstellar medium. In particular, when two isolated massive stars are relatively close and explode, the resulting Supernovae Remnants (SNRs) can interact. The impact zone presents fascinating complex hydrodynamic physics which depends on the age of the SNRs, their relative evolution stage, and the distance between the two stars. In this Letter, we investigate experimentally the interaction region (IR) formed when two blast waves (BWs) collide during their Taylor-Sedov expansion phase. The two BWs are produced by the laser irradiation (1 ns, ∼500 J) of 300 μm diameter carbon rods and propagate in different gases (Ar and N2) at different pressures. The physical parameters, such as the density and temperature of the IR, are measured for the first time using a set of optical diagnostics (interferometry, schlieren, time-resolved optical spectroscopy, etc.). This allows us to determine precisely the thermodynamic conditions of the IR. A compression ratio of r ∼ 1.75 is found and a 17–20% increase in temperature is measured compared to the shell of a single blast wave. Moreover, we observe the generation of vorticity, inducing strong electron density gradients, in the IR at long periods after the interaction. This could in principle generate magnetic fields through the Biermann Battery effect. [ABSTRACT FROM AUTHOR]

We report time-resolved X-ray Absorption Near Edge Spectroscopy (XANES) measurements of warm dense MgO. We used a high power nanosecond pulse to drive a strong uniform shock wave into an MgO sample, and a picosecond pulse to generate a broadband X-ray source near the Mg K-edge. We used this setup to obtain XANES spectra across a large area of the phase diagram, with densities up to 6.8 g/cc and temperatures up to 30 000 K, conditions at which no prior investigations of electronic and ionic structure exist. Our XANES results, together with quantum molecular dynamic simulations, demonstrate that the sample metallizes due to the bandgap closure as it melts, after which it shows typical behavior for a disordered ionic liquid. [ABSTRACT FROM AUTHOR]

Two partially coherent light laser beams, coupled with a random phase plate were focused at an angle of 31.7° with the centers of the beams offset by 250 μm. This produced a relatively uniform (7% root-mean-square) irradiated spot of 400 μm. When this technique was used to produce a shock wave in a copper wedge, a relatively uniform shock of 2 ns duration was produced. In addition, a multilayered flyer plate was accelerated using this method to an average speed of 21 km/s and produced a planar impact on a glass window. It is anticipated that this technique can be used to produce important multi-Mbar equation of state information in future experiments. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Reports on the results of the experiments of flyer acceleration by the irradiation of a high power laser using the ASHURA system. Ablation of the aluminum and polyimide layers by the laser; Acceleration of the rear layer as a flyer; Suggestion that the tantalum flyer is in a condensed state for the duration of the flight; Estimation of the flyer velocity from the acceleration profile.

The response of lithium fluoride (LiF) crystal detectors to monochromatic X-rays is measured in the multi-kilo-electron-volt range. This response, as a function of the X-ray dose, is independent of photon energy with no saturation level found. The response, as a function of the incident energy flux, is found to increase for photons of lower energy due to the differing attenuation lengths of X-ray photons within the crystal. Small differences are seen between different confocal microscopes used to scan the data, suggesting the need for absolute calibration. The spatial resolution of the LiF is also measured (1.19–1.36 μm) and is found to be independent of incident photon energy. Finally, a photometric study is performed in order to assess the feasibility of using these detectors at current X-ray free electron laser and laser facilities worldwide. [ABSTRACT FROM AUTHOR]

In this work, we demonstrate simultaneous phase-contrast imaging (PCI) and X-ray diffraction from shock compressed matter at the Matter in Extreme Conditions endstation, at the Linac Coherent Light Source (LCLS). We utilize the chromaticity from compound refractive X-ray lenses to focus the 24.6 keV 3rd order undulator harmonic of the LCLS to a spot size of 5 μm on target to perform X-ray diffraction. Simultaneous PCI from the 8.2 keV fundamental X-ray beam is used to visualize and measure the transient properties of the shock wave over a 500 μm field of view. Furthermore, we demonstrate the ability to extend the reciprocal space measurements by 5 Å−1, relative to the fundamental X-ray energy, by utilizing X-ray diffraction from the 3rd harmonic of the LCLS. [ABSTRACT FROM AUTHOR]

Pressure, density, and temperature were measured along the principal Hugoniot of the Si-doped Glow Discharge Polymer used in Inertial Confinement Fusion (ICF) capsules up to 5 Mbar, covering conditions beyond the first shock in a full-scale Inertial Confinement Fusion (ICF) capsule. The experiments were performed using the GEKKOXII laser at the Institute of Laser Engineering at Osaka University in Japan. Results are in good agreement with predictions obtained from ab initio Hugoniot calculations, but softer than the quotidian equation of state average atom model. Ab initio calculations show that dissociation of carbon bonds need to be taken into account in order to explain Hugoniot compressibility. [ABSTRACT FROM AUTHOR]

The development of small sized laser operating above room temperature is important in the realization of optical integrated circuits. Recently, micro-lasers consisting of photonic crystals (PhCs) and whispering gallery mode cavities have been demonstrated. Optically pumped laser devices could be easily designed using photonic crystal-slab waveguides (PhC-WGs) with an air-bridge type structure. In this study, we observe lasing at 1.3μm from two-photon pumped InAs-quantum-dots embedded GaAs PhC-WGs above room temperature. This type of compact laser shows promise as a new light source in ultra-compact photonics integrated circuits. [ABSTRACT FROM AUTHOR]

In this paper, we report on the quasi-isentropic compression of an iron sample using ramp shaped laser irradiation. This technique allows us to quasi-isentropically compress iron up to 700GPa and 8500K. To our knowledge, these data are the highest pressures reached on iron in off-Hugoniot conditions and the closest to the thermodynamic states thought to exist in Earth-like planetary cores. The experiment was performed on the Ligne d'Intégration laser facility at CESTA, Bordeaux, France. [ABSTRACT FROM AUTHOR]

Pressure, density, temperature, and reflectivity measurements along the principal Hugoniot of Ge-doped plastics used in Inertial Confinement Fusion capsules surrogates were obtained to pressures reaching up to 7 Mbar and compared to Quotidian Equation of State models. The experiment was performed using the GEKKO XII laser at the Institute of Laser Engineering at Osaka University in Japan. High precision measurements of pressure and density were obtained using a quartz standard and found to be in good agreement with theoretical Hugoniot curves. Modeling of reflectivity measurements show that shocked samples can be described as poor metals and that mean ionization calculated within the frame of QEOS is overestimated. Similarly, shock temperatures were found to be below theoretical Hugoniot curves. [ABSTRACT FROM AUTHOR]

Laser shock compression experiments on precompressed samples offer the possibility to explore extreme material states unreachable by static or single-shock compression techniques alone. We have found significant increases in static compression pressure in a wide-opening and thin diamond precompression cell. This suggests that the precompression target is adaptable to advanced coupling techniques with laser-driven dynamic compression methods. The novel coupling techniques proposed give the potential to access outstanding material states required in planetary and condensed-matter physics. [ABSTRACT FROM AUTHOR]

This paper reports an experimental study on preheating of laser-irradiated targets. We performed temperature measurements at the rear surface of laser-irradiated targets under conditions of two different laser wavelengths (0.35 or 0.53 μm) and several intensities (2×1013–1×1014 W/cm2) in order to verify an effect of radiation and nonlocal electron heat transport. The preheating temperature was evaluated by observing self-emission, reflectivity, and expansion velocity at the rear surface of planar polyimide foils. The experimental results show that the x-ray radiation is dominant for preheating for 0.35-μm laser irradiation, but contribution of nonlocal electron heat transport is not negligible for 0.53-μm laser irradiation conditions. [ABSTRACT FROM AUTHOR]

Equation-of-state data, not only pressure and density but also temperature, for polystyrene (CH) are obtained up to 510 GPa. The region investigated in this work corresponds to an intermediate region, bridging a large gap between available gas-gun data below 60 GPa and laser shock data above 500 GPa. The Hugoniot parameters and shock temperature were simultaneously determined by using optical velocimeters and pyrometers as the diagnostic tools and the α-quartz as a new standard material. The CH Hugoniot obtained tends to become stiffer than a semiempirical chemical theoretical model predictions at ultrahigh pressures but is consistent with other models and available experimental data. [ABSTRACT FROM AUTHOR]

Studies of short-pulse laser-generated hard x-ray (18–60 keV) sources, suitable for radiographs of large samples of dense matter, are presented. The spatial and dynamic resolutions for different target types and laser parameters have been investigated. A high quality radiograph with good spatial resolution in two dimensions was demonstrated by irradiating freestanding thin W wires. The influence of the geometry for the quality of the radiograph, which is crucial for the design of experiments probing laser-compressed matter, is reported. [ABSTRACT FROM AUTHOR]

In this letter we report on the direct density measurement in a shock compressed aluminum target using hard x-ray radiography. Experimental data employing a molybdenum Kα source at 17.5 keV, generated with a short pulse laser are presented. High spatial resolution was obtained thanks to a new design for the backlighter geometry. Density values deduced from radiography are compared to predictions from hydrodynamic simulations, which have been calibrated in order to reproduce shock velocities measured from a rear-side self-emission diagnostic. Our results reveal the great potential of this technique as a diagnostic tool for direct density measurements in dense high-Z opaque materials. [ABSTRACT FROM AUTHOR]

In this paper, experimental results on radiative shocks generated by a high power laser in a xenon gas cell are presented. Two sets of experiments have been performed at the Laser pour l'Utilisation des Lasers Intenses (LULI) laboratory. Several shock parameters were simultaneously measured: shock temperature and velocities, the precursor two-dimensional (2D) time evolution, its electron density, density gradient, and temperature. Data were obtained varying initial conditions for different laser intensities and gas pressures. Comparisons with 1D and 2D radiative hydrodynamic simulations are shown for all measured parameters (shock velocity, shape, radial expansion, and temperature as well as precursor velocity and electron density). [ABSTRACT FROM AUTHOR]

Hugoniot data of diamond was obtained using laser-driven shock waves in the terapascal range of 0.5–2 TPa. Strong shock waves were generated by direct irradiation of a 2.5 ns laser pulse on an Al driver plate. The shock wave velocities in diamond and Al were determined from optical measurements. Particle velocities and pressures were obtained using an impedance matching method and known Al Hugoniot. The obtained Hugoniot data of diamond does not show a marked difference from the extrapolations of the Pavlovskii Hugoniot data in the TPa range within experimental errors. [ABSTRACT FROM AUTHOR]

Equation-of-state (EOS) measurements for polystyrene in TPa (10 Mbar) pressure regions are presented. Polystyrene Hugoniot data were obtained up to 2.7 TPa using impedance matching techniques with laser direct drive at the GEKKO/HIPER laser facility [N. Miyanaga et al., in Proceedings of the 18th International Conference on Fusion Energy (IAEA, Sorrento, Italy, 2001), IAEA-CN-77] The results were compared with theoretical models and previous experimental data and found to be in good agreement with the previous data obtained by different drive and diagnostic techniques. [ABSTRACT FROM AUTHOR]

The GEKKQ/HIPER-laser [N. Miyanaga et al., in Proceedings of the 18th International conference on Fusion Energy (IAEA, Sorrento, Italy, 2001), IAEA-CN-77] driven shock experiments were characterized in detail for studies on equation-of-state (EOS) at ultrahigh pressures. High-quality shock waves were produced with the bundled 9 laser beams optically smoothed by spectral dispersion technique and Kinoform phase plates. The laser beams were directly focused on targets at up to an intensity of 1014 W/cm² or higher with a wavelength of 351 nm and a duration of 2.5 ns. Key issues on dynamic EOS research; the spatial uniformity and temporal steadiness of shock wave were estimated, and the preheating problem was also investigated by measurements of the self-emission and reflectivity from target rear surface. The experimental and analytical methods were validated by using double-step targets consisting of two Hugoniot standard metals. Extreme pressures only accessed in nuclear explosion experiments were generated with reproducibility and good accuracy using the laser direct-drive experimental system, for Al, Cu, polystyrene, and Ta. It was indicated that new and reliable EOS data at the ultrahigh pressures could he provided for materials ranging from low to high initial density by the laser direct-drive experimental technique. [ABSTRACT FROM AUTHOR]

Equation-of-state measurements for a polyimide are presented. High-power KrF laser and chemical explosive-driven experiments provided Hugoniot data on the polyimide up to about 65 GPa. Conventional reflected-light measurements in the explosive experiments and velocity interferometry measurements in the laser experiments were performed. From both laser and explosive results the change of Hugoniot was indicated at near 30 GPa. [ABSTRACT FROM AUTHOR]

Electric and magnetic properties were investigated on p-type Zn1-xCrxTe doped with nitrogen (N) as an acceptor. Thin films of p-Zn1-xCrxTe (x≤=0.09) were grown by molecular-beam epitaxy with the supply of N2 gas excited by rf plasma. With the increase of Cr composition x at an almost fixed N concentration of the order of 1020 cm-3, the temperature dependence of resistivity changed from metallic behavior to an insulating one, accompanied with a significant decrease of the hole concentration. The magnetization measurements revealed that ferromagnetic behaviors observed in undoped Zn1-xCrxTe were suppressed due to the nitrogen doping; with N concentrations of the order of 1020 cm-3, hysteresis loops in the magnetization curve disappeared, the magnitude of magnetization decreased, and the ferromagnetic transition were not observed down to 2 K according to the Arrott plot analysis. These experimental findings are discussed on the basis of the ferromagnetic double exchange interaction which is considered to work on the Cr 3d impurity level formed in the band gap of ZnTe. [ABSTRACT FROM AUTHOR]

We have observed the formation process of nanocatalysts that act for the growth of Si nanowires by means of UHV scanning tunneling microscopy. Gold-silicon nanocatalysts that we have examined were thought to form on a hydrogen (H)-terminated [111] silicon surface and to expel Si nanowires of extremely high aspect ratio via the vapor-liquid-solid mechanism. We have observed that a nanocatalyst, that is, a droplet of melted gold-silicon alloy of about 5 nm in diameter, is actually formed in a pit on a H-terminated surface in the narrow temperature range around 500°C. We have concluded that, in this specific temperature range, nanocatalysts can be melted, remain mutually isolated, absorb silicon effectively, and expel Si nanowires. Based on the result, we have proposed a method of making a thin template, which facilitates to decide the nucleation sites and the sizes of nanocatalysts, resulting in the precise control of those of Si nanowires. [ABSTRACT FROM AUTHOR]