Bulletin of the American Physical Society
15th APS Topical Conference on Shock Compression of Condensed Matter
Volume 52, Number 8
Sunday–Friday, June 24–29, 2007; Kohala Coast, Hawaii
Session B5: Spectroscopy and Optical Studies I |
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Chair: Joel Carney, Naval Surface Warfare Center Room: Fairmont Orchid Hotel Plaza III |
Monday, June 25, 2007 10:30AM - 11:00AM |
B5.00001: Optical Response of Molecular Crystals to Non-hydrostatic Compression in a Diamond Anvil Cell Experiments Invited Speaker: High pressure response of molecular crystals is not as well understood as the response of covalent or ionic crystals. Because molecular crystals are highly compressible, small variations in applied stresses result in large intermolecular changes. Additionally, low symmetries, characteristic of molecular crystals, result in significant deformation under static pressure loading. Hence, an understanding and controlling of non-hydrostatic effects are important for examining molecular crystals. Several examples will be presented to show the significance of non-hydrostaticity on the underlying molecular mechanisms in a diamond anvil cell experiments. In particular, we will present our work on selected molecular crystals to highlight the role of non-hydrostaticity on: (i) structural phase transitions, (ii) changes in electronic structure, (iii) formation of structural defects, and (iv) solid state reactivity. Finally, we will demonstrate a relevance of non-hydrostatic compression to shock wave experiments. Work supported by DOE and ONR. [Preview Abstract] |
Monday, June 25, 2007 11:00AM - 11:15AM |
B5.00002: Brillouin-scattering Determination of the Acoustic Properties of Polymers at High Pressure Dana Dattelbaum, Lewis Stevens, Edward Orler, Muhtar Ahart, Russell Hemley Brillouin scattering is a powerful tool for probing the elastic properties of materials. Coupled with high pressure environments, such as those accessible using diamond anvil cells, the method can reveal rich materials physics under extreme conditions, and provide fundamental data for the development of equations-of-state. For the first time, the acoustic properties of three polymeric elastomers have been measured from ambient pressure to 12 GPa. While both transverse and longitudinal modes were observed for all three polymers, transverse modes were only observed at elevated pressures, with the pressure on-set of observable modes differing for the polymers studied. From the measured acoustic properties, elastic constants, moduli, and Poisson's ratios were calculated as a function of pressure. P-V isotherms were also constructed, and fit to a range of empirical/semi-empirical isothermal equation-of-state (EOS) forms. From this analysis, the isothermal bulk modulus and its pressure derivative were obtained for the polymers interrogated, and the static results were compared to available shock wave compression data. [Preview Abstract] |
Monday, June 25, 2007 11:15AM - 11:30AM |
B5.00003: Time-resolved emission spectroscopy of transparent and nontransparent materials. Takamichi Kobayashi, Toshimori Sekine Time-resolved emission spectroscopy with pulsed excitation has been used to observe spectral changes of shocked transparent single crystals and nontransparent materials. For transparent single crystals, drastic spectral changes near the HEL are observed and Us-Up relations can be determined. As the shock pressure is increased in the plastic region, however, the emission intensity decreases rapidly, probably because plastic deformation develops with pressure. For nontransparent materials, measurements of emission spectra under shock compression appears more difficult than transparent materials. Results on powder materials will be presented. [Preview Abstract] |
Monday, June 25, 2007 11:30AM - 11:45AM |
B5.00004: Photoacoustic Measurements to Determine Acoustic Velocities in Shocked Liquids N. Hemmi, K. Zimmerman, J.M. Winey, Y.M. Gupta, D.H. Torchinsky, K.A. Nelson Experimental developments were carried out to implement the Impulsively Stimulated Thermal Scattering (ISTS) method in shock wave experiments. This method, an application of Brillouin scattering in the time domain, allows us to determine the sound velocity and acoustic damping properties under dynamic loading in single event experiments. We discuss our experimental developments where the capability for performing reproducible single-shot experiments is key. We also present experimental results for benzene and glycerol, highlighting the differences in the shock response for these two liquids. Sound velocities were clearly observed for benzene shocked up to 0.85 GPa, while ISTS signals from shocked glycerol could not be observed due to strong acoustic damping. Implications of these photoacoustic measurements for understanding the shocked state will be presented. Work supported by DOE and ONR. [Preview Abstract] |
Monday, June 25, 2007 11:45AM - 12:00PM |
B5.00005: A shock pressure induced phase transition from liquid to solid of cyclohexane using time-resolved coherent anti-Stokes Raman spectroscopy Shiro Oguchi, Akira Sato, Ken-ichi Kondo, Kazutaka Nakamura The liquid-solid phase transition of cyclohexane has been studied under laser shock compression up to 3.8 GPa by using nanosecond time-resolved Coherent Anti-stokes Raman Spectroscopy (CARS) and laser shock compression. The shock wave is generated by irradiation of 10 ns pulsed laser beam on the plasma confinement target and its pressure is estimated from a particle velocity, which is measured by optically recording velocity interferometer system (ORVIS). Higher frequency shift of the Raman peaks (ring-breathing, C-C stretching, and CH$_{2}$ twist modes) was observed at high pressure. At 3.8 GPa, splitting of the peak (CH$_{2}$ twist mode) due to change in symmetry of surrounding molecules, which corresponds to phase transition to solid IV, was observed at delay time of 20 ns. Rapid liquid-solid phase transition has been directly observed to occur within 20 ns. [Preview Abstract] |
Monday, June 25, 2007 12:00PM - 12:15PM |
B5.00006: Ultrafast shock wave coherent dissociation and spectroscopy of materials Dana Dlott, Zhaohui Wang, Alexei Lagutchev, Jeffrey Carter, David Cahill This research is focused on understanding what happens at the level of individual molecules, when a solid is broken into two pieces creating a nascent interface. Ordinarily breaking a material involves nucleation or crack formation, so that at a given instant every atom at the interface acts differently. In order to get at detailed mechanisms it is desirable to have every atom doing exactly the same thing, in other words to cause the material to dissociate coherently. In this talk we will discuss methods for creating coherence in the dissociation process using femtosecond laser-driven tensile shocks, and methods for probing the molecular structures and energy dissipation processes in atomic layers immediately adjacent to the interface, using nonlinear and coherent optical spectroscopies. This material is based upon work supported by the U.S. Department of Energy, Division of Materials Sciences under Award No. DEFG02-91ER45439, through the Frederick Seitz Materials Research Laboratory at the University of Illinois at Urbana-Champaign. [Preview Abstract] |
Monday, June 25, 2007 12:15PM - 12:30PM |
B5.00007: Optical Properties, Raman Scattering, and Radiometry of Diamond under Shock Compression. R. Stewart McWilliams, Dylan K. Spaulding, Raymond Jeanloz, Jon H. Eggert, Peter M. Celliers, Damien G. Hicks, Gilbert W. Collins We have studied the optical transparency, luminescence, index of refraction, and elastic-plastic relaxation of diamond shocked to pressures in excess of its elastic limit. Techniques include VISAR velocimetry, optical pyrometry, and spontaneous Raman scattering on quasi-steady shock compressions in crystallographic orientations (100), (110), and (111) driven by the kiloJoule Janus laser at Lawrence Livermore National Laboratory. We extend the pressures to which diamond, or any material, has been studied using Raman scattering, and explore the development of two-wave, elastic-plastic compression near the Hugoniot Elastic Limit. This work was performed under the auspices of the U.S. Department of Energy. by Lawrence Livermore National Laboratory under contract No. W-7405-Eng-48. [Preview Abstract] |
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