Bulletin of the American Physical Society
2005 14th APS Topical Conference on Shock Compression of Condensed Matter
Sunday–Friday, July 31–August 5 2005; Baltimore, MD
Session Q3: Spectroscopy & Optical Properties II |
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Chair: Neil Holmes, Lawrence Livermore National Laboratory Room: Hyatt Regency Constellation D |
Wednesday, August 3, 2005 9:30AM - 9:45AM |
Q3.00001: Optical characterization of defects in RDX Von Whitley The objective of this work was to study the effects of impurities and defects on the absorption spectra of RDX. RDX is known to exhibit a sample-to-sample variation in the shock and impact sensitivity. There have been a number of explanations for the variation in the sensitivity, from small voids, to molecular impurities, to dislocations of the crystalline lattice. Ultimately, the reason is still debated, but it is generally accepted that higher-quality crystals are less sensitive than lower-quality crystals. Simple methods to determine the quality of RDX crystals are needed. Defects in the crystalline lattice, whether it is an impurity, a vacancy or a dislocation, will interrupt the crystalline symmetry around the defect. This interruption of the crystalline symmetry can be optically detected via anomalous absorption features found in the normally forbidden band gap region. This could allow for a simple experimental method to determine the quality of RDX. [Preview Abstract] |
Wednesday, August 3, 2005 9:45AM - 10:00AM |
Q3.00002: Liquid-solid phase transition of benzene under shock compression studied by nanosecond time-resolved nonlinear Raman spectroscopy Kazutaka Nakamura, Akitaka Matsuda, Ken-ichi Kondo Phase transition of benzene has been studied under laser-shock compression up to 4.2 GPa by using nanosecond time-resolved nonlinear Raman spectroscopy. 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 a velocity interferometer system. Higher frequency shifts in the ring- breathing mode of benzene are observed under shock compression. The shift at pressures below 3.0 GPa agrees well with that of liquid benzene under static compression. A metastable supercooled state and a liquid-solid phase transition are observed at shock pressures above 3.0 GPa. Time-resolved Raman spectra reveal that the liquid state is initially a metastable state and rapidly transforms to the solid state under shock compression at 4.2 GPa. Rapid nucleation and growth occurs within 20 ns. [Preview Abstract] |
Wednesday, August 3, 2005 10:00AM - 10:15AM |
Q3.00003: Shock-Induced Electronic Structure Changes in Anthracene Single Crystals using Time-Resolved Spectroscopy Naoki Hemmi, Zbigniew Dreger, Yogendra Gupta Shock-induced changes in the electronic structure of anthracene single crystals were investigated up to 6 GPa using optical spectroscopy. Absorption experiments revealed significant changes in the electronic structure of anthracene crystals under shock compression: (i) monotonic red shift of the band edge of monomer absorption, (ii) a new broad and structureless band on the lower energy side of the red-shifted band. In laser induced fluorescence measurements, excimer-like fluorescence was observed following the excitation in the new absorption band. These results indicate the formation of new electronic states in shocked anthracene. The new states are attributed to dimer-type defects formed as a result of the high stress and plastic deformation due to shock loading. Work supported by DOE and ONR. [Preview Abstract] |
Wednesday, August 3, 2005 10:15AM - 10:30AM |
Q3.00004: Optical Absorption and Raman Spectroscopy of Multiple Shocked Liquid Benzene to 10 GPa S. Root, Y.M. Gupta Liquid benzene samples were multiply shocked to peak pressures ranging from 3 GPa to 10 GPa to examine physical and chemical changes in benzene. A xenon flashlamp was used to probe the visible spectrum of benzene for loses in transmitted light intensity caused by changes in the electronic structure (absorption) or a possible liquid to solid phase transition (scattering). Raman spectroscopy was used to corroborate transmission measurements by examining changes in the benzene vibrational modes. The C-C symmetric ring breathing mode (992 cm$^{-1})$, C-H symmetric stretch (3061 cm$^{-1})$, along with several weaker modes at 607 cm$^{-1}$, 1178 cm$^{-1}$, 1586 cm$^{-1}$, and 1606 cm$^{-1}$ were monitored during shock loading. An EOS was developed to calculate the temperature of the shock compressed benzene. The present work has demonstrated that liquid benzene remains unchanged during multiple shock loading up to 10 GPa. Work supported by ONR and DOE. [Preview Abstract] |
Wednesday, August 3, 2005 10:30AM - 10:45AM |
Q3.00005: Ultrafast double pass absorption in benzene and cyclohexane Ricky Chau, Neil C. Holmes In this study, we report preliminary double-pass absorption experiments on benzene and cyclohexane. For these experiments, a high power broadband light source was used and the light was collected using both photomultiplier tubes and a streak cameras. The light on the PMTs were recorded at different wavelengths. We will present the results from the inital experiments with a discussion of the time resolved dissociation of the benzene and cyclohexane and a comparison of benzene (carbon double bonds) and cyclohexane (carbon single bonds).\\\\ This work was performed under the auspices of the U.S. Department of Energy by University of California, Lawrence Livermore National Laboratory under Contract W-7405-Eng-48. [Preview Abstract] |
Wednesday, August 3, 2005 10:45AM - 11:00AM |
Q3.00006: Velocity Correction for [100] LiF Optical Windows under Shock Compression, Recompression, and Unloading B. LaLone, O. Fataynov, J. Asay, Y. Gupta LiF is a standard optical window for interferometric measurements in shock wave experiments. It is generally assumed that the velocity correction, derived from single shock measurements, is applicable for arbitrary profiles. To determine the validity of this assumption, two types of experiments were carried out to determine velocity correction in compression, unloading, and recompression experiments. In the first, [100] LiF crystals were subjected to initial shock stresses ranging from 4 -- 17 GPa, and unloaded completely. In the second set of experiments, [100] LiF crystals were subjected to initial shock stresses ranging from 5 -- 11 GPa, and recompressed to 8 -- 17 GPa. Velocity corrections were measured using experimental configurations in which the velocity of the reflecting surface is independently known. The present results show that, within experimental error, the velocity correction for LiF windows depends only on the particle velocity and is independent of the loading history. Work supported by DOE. [Preview Abstract] |
Wednesday, August 3, 2005 11:00AM - 11:15AM |
Q3.00007: Suitability of magnesium oxide as a VISAR window Gerald Stevens, Lynn Veeser, Paulo Rigg, Robert Hixson Impedance matching of a VISAR window to a material under study helps simplify a shock experiment by effectively allowing one to measure an in situ particle velocity. The shock impedance of MgO falls roughly midway between those of sapphire and LiF, two of the most frequently used VISAR window materials. A series of symmetric impact experiments were performed to characterize the suitability of single crystal, [100] oriented magnesium oxide as a VISAR window material. These experiments yielded good results and show the viability of MgO as a VISAR window up to 23 GPa. Results from these experiments were used to determine window correction factors, and subsequently to estimate the pressure induced change in index of refraction. In many of the shots in this work we exceeded the Hugoniot elastic limit, and both elastic and plastic waves are evident in the velocity profiles. The presence of both waves within the VISAR window complicates the typical VISAR window correction analysis. Preliminary analysis of the elastic and plastic contributions to the window correction is presented. [Preview Abstract] |
Wednesday, August 3, 2005 11:15AM - 11:30AM |
Q3.00008: Hypervelocity Impact Flash at 6, 11, and 25 KM/S R.J. Lawrence, W.D. Reinhart, L.C. Chhabildas, T.F. Thornhill Impact-flash phenomenology has been known for many years, and is now being considered for missile-defense applications, in particular, remote diagnostics for kill assessment and target typing. To technically establish this capability, we have conducted a series of experiments at impact velocities of $\sim $6, $\sim $11, and $\sim $25 km/s. Two- and three-stage light-gas guns were used for the lower two velocities, and magnetically-driven flyers on the Sandia Z machine achieved the higher velocity. Spectrally- and time-resolved flash output addressed data reproducibility, material identification, and target configuration analysis. Usable data were obtained in the visible and infrared regions of the spectrum. Data from the Z shots extended for nearly 0.5 $\mu $s, and from the gas-guns usable reading times lasted for $\sim $100 $\mu $s. Standard atomic spectral databases were used to identify strong lines from all the principle materials used in the study. The data were unique to the individual materials over the wide range of velocities and conditions examined. The time-varying nature of the signals enabled correlation of differing spectra with multi-layer targets containing different materials in the separate layers. Integrating the records over wavelength helped to clarify those time variations. (*)Sandia is a multiprogram laboratory operated by Sandia Corporation, a Lockheed Martin Company, for the US Department of Energy's National Nuclear Security Administration under contract DE-AC04-94AL85000. [Preview Abstract] |
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