Bulletin of the American Physical Society
16th APS Topical Conference on Shock Compression of Condensed Matter
Volume 54, Number 8
Sunday–Friday, June 28–July 3 2009; Nashville, Tennessee
Session T4: SO-3: Spectroscopy 3 |
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Chair: Jared Gump, NSWC - Indian Head Room: Hermitage D |
Thursday, July 2, 2009 9:00AM - 9:15AM |
T4.00001: Laser-driven flyer plates for reactive materials research Hiroki Fujiwara, Kathryn Brown, Rusty Conner, Dana Dlott We have developed a laser-driven flyer plate apparatus to study shock-induced chemistry of reactive materials (RM) containing Al nanoparticles. Reactive materials are generally composed of fuel and oxidizer particles. Under shock compression these components mix and react to liberate energy and do work. Understanding how shocked nanoparticle compositions undergo exothermic chemistry is a difficult problem in materials science, since the reactivity is a function of both chemical and materials parameters. Laser-launched flyer plates coated with a small amount of the RM are made to impact a window and their emission spectrum is studied. Achieving a good reproducible launch is a problem, and is generally limited by the quality of the laser beam profile and the flyer target. Our approach exploits recent advances in beam shaping and microfabrication. This material is based on work supported by the US Army Research Office under award number W911NF-04-1-0178 and the Air Force Office of Scientific Research under award number FA9550-06-1-0235. Kathryn Brown acknowledges support from the Stewardship Sciences Academic Alliance Program from the Carnegie-DOE Alliance Center under grant number DOE CIW 4-3253-13. [Preview Abstract] |
Thursday, July 2, 2009 9:15AM - 9:30AM |
T4.00002: Single shot ultrafast dynamic ellipsometry of laser-driven shocks in single crystal explosives and thin films of metals Von Whitley, Shawn McGrane, David Moore, Dan Eakins, Cynthia Bolme Ultrafast dynamic ellipsometry (UDE) was used to measure the shock conditions of single-crystal energetic materials and metal thin films. Explosive crystals are coated with aluminum, which through frustrated laser ablation acts as a shock drive layer. UDE data on shocked explosives and different potential metal drive layers will be reported and experimental considerations will be discussed. [Preview Abstract] |
Thursday, July 2, 2009 9:30AM - 9:45AM |
T4.00003: Probing energetics with second harmonic generation Christopher Konek, Brian Mason, Chad Stoltz, Jared Gump, John Wilkinson We focus on the insensitive high explosive 1,3,5-triamino-2,4,6- trinitrobenzene (TATB) with the goal of obtaining structural information as a function of pressure and temperature. Prior experiments from Los Alamos (Son et al. J. Phys. Chem. B. 1999, 103 (26) 5434) demonstrated that in high temperature environments (approaching 300$^{\circ}$ C) TATB increases in efficiency as a nonlinear optical medium, possibly undergoing structural changes which alter the crystal symmetry. We use the nonlinear optical technique second harmonic generation (SHG) to probe TATB in a diamond anvil cell experimental setup to perform measurements at high pressure. Additionally, by exploiting the electronic absorption features of TATB to perform resonantly enhanced second harmonic generation (RE-SHG) experiments, we probe the electronic transitions in the visible range as a function of pressure and temperature, to observe electronic changes that would occur. Polarization resolved SHG experiments allow further insight into changes in crystal structure. These static measurements may have implications for shocked TATB. [Preview Abstract] |
Thursday, July 2, 2009 9:45AM - 10:00AM |
T4.00004: Measurement of optical extinction coefficients in sapphire as a function of the shock pressure Xianming Zhou, Jun Li, Jiabo Li Sapphire has been extensively used as a window material for both optical and thermal property measurements of shocked materials. Its optical extinction characteristic under dynamic compression is crucial in understanding the measured physical behaviors. Here we demonstrated a quantitative study of the dynamic optical extinction of sapphire in the shock pressure range from 72 to 183 GPa. Along its $<$1000$>$ orientation, the optical extinction coefficient ($\alpha )$ of sapphire crystal has been in-situ measured at several discrete wavelengths with an optical pyrometer incorporated with a shock-generated bright light source. The significant findings indicated that: (i) the $\alpha $ coefficient increases with the shock pressure but decreases with the wavelength, showing a quite different behavior from that observed in the low-pressure compression in the literature; (ii) the obtained linear relationship between the square-root of $\alpha $ coefficient and the photon energy can be well described by a Mie scattering calculation assuming a particle radii of $\sim $140nm, which suggests that the optical extinction of sapphire is attributed to a light scattering mechanism related with the shock-induced crack-net distribution in this strong brittle material. These quantitative extinction data have provided new insight into the decay nature of thermal radiance histories previously concerned at a metal/sapphire interface, which is crucial for inferring an interfacial equilibrium temperature. [Preview Abstract] |
Thursday, July 2, 2009 10:00AM - 10:15AM |
T4.00005: Effects of radiation damage in semiconductors using picosecond compressional waves Andrew Steigerwald, Justin Gregory, Ying Xu, Jingbo Qi, Norman Tolk Coherent acoustic phonon (CAP) interferometery is an ultrafast pump-probe optical technique wherein a traveling nano-acoustic wave samples, layer by layer, the properties of thin film heterostrucutres or nanostructured materials. Here we use sensitivity of the CAP technique to analyze the effects of extended ion irradiation in GaAs wafers. During ion irradiation multiple defects are created per ion, resulting in a continuous Gaussian-like damage profiles with full widths on the order of 500nm. The presence of such defects acts to modify local wavefunctions, resulting in degradation of the optoelectronic properties. We present results wherein (a) quantitative defect concentration profiles are measured as a function of depth, and (b) the severity of the electronic structure modifications in GaAs are measured as a function of defect concentration. The former represents a novel characterization technique with sensitivity and depth limits surpassing current techniques, while the latter represents unique measurements of the band structure in radiation damaged GaAs. [Preview Abstract] |
Thursday, July 2, 2009 10:15AM - 10:30AM |
T4.00006: Optical studies of III-V semiconductors under shock and ramp wave loading Paulius Grivickas, Matt McCluskey, Yogendra Gupta Low temperature photoluminescence of GaP and GaAs was investigated under conditions of uniaxial strain generated using shock and ramp wave loading along the [100], [111], and [100] orientations. In GaP, the exact band gap shifts were measured up to 5 GPa longitudinal stress and accurate optical deformation potentials of GaP were derived. The parameters established were used to explain nonlinear optical response and ionization of isoelectronic nitrogen impurities in shocked GaP. In GaAs, the crossing between the direct and the indirect conduction bands was observed below 5.5 GPa for all loading orientations. The exact transitions for different orientations were obtained by correlating the PL intensity changes in ramp wave experiments with simultaneous VISAR measurements. Modeling of this phenomenon showed that unlike hydrostatic pressure, where the direct-to-indirect transition is possible only between G and X conduction bands, the shear component of uniaxial strain can produce the transition between G and L bands as well. As the result, the accurate deformation potentials of all three conduction bands of GaAs were derived. [Preview Abstract] |
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