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 L5: Spectroscopy and Optical Studies III |
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Chair: Zbigniew Dreger, Washington State University Room: Fairmont Orchid Hotel Plaza III |
Wednesday, June 27, 2007 8:00AM - 8:30AM |
L5.00001: Single Shot Dynamic Ellipsometry Measurements of Laser-Driven Shock Waves Invited Speaker: A technique has been developed to measure the time-resolved position of a laser-driven shock wave and the subsequent material flow. Ultrafast Dynamic Ellipsometry using a chirped femtosecond laser pulse probes picosecond material dynamics in a single shot by capitalizing on the refractive index changes in the material. For transparent materials, the shock velocity, the particle velocity, and the shocked material's refractive index are extracted. A range of Hugoniot data is measured by taking advantage of the Gaussian spatial profile of the shock-driving laser that generates a distribution of pressures in the shocked media. Details of the experimental technique will be presented along with results from its application to transparent thin films. [Preview Abstract] |
Wednesday, June 27, 2007 8:30AM - 8:45AM |
L5.00002: Common Problems with Pyrometry at Shock Physics Experiments and How to Avoid Them Achim Seifter, Andrew Obst, David Holtkamp Temperature is not only one of the most prominent parameters in shock physics experiments but also very hard to determine experimentally. Only a few techniques are available because of difficulties due to the short timescale and often very low temperatures. Pyrometry is the most portable of these techniques but has to deal with some problems which give rise to uncertainties. Only if the experiment is designed very carefully some of these difficulties like background radiation from high explosive burn products, muzzle flash or laser light can be avoided. Other problems like spatial temperature non-uniformities or thermal radiation from a transparent anvil are inherent to the experiment and cannot be avoided. By choosing the proper spectral range covered by the pyrometer and fitting the obtained spectral radiance traces with appropriate models meaningful results can be obtained. In this paper we will describe the most important points to be taken into account when designing the experiment, present considerations for choosing the wavelength range of the pyrometer and show data where spatial non uniformities or radiation from hot anvils occurred and temperature data could still be obtained. [Preview Abstract] |
Wednesday, June 27, 2007 8:45AM - 9:00AM |
L5.00003: Emission spectroscopy of aluminum in post-detonation combustion John Wilkinson, Richard Lee, Joel Carney Emission spectroscopy measurements were performed on the fuel-rich explosive formulation PBX-N113 to determine the temperature and pressure in the post-detonation combustion plume. Specifically, the emission of aluminum was interrogated to determine the temperature and pressure of the atomic species in the debris field. Pressures in a detonation can exceed 100 kbar and temperatures can exceed 4000 K. Collisional broadening of gas phase atoms and molecules in this extreme environment causes the emission lines to be measurably broadened. In this paper, we discuss collision-broadened aluminum emission spectra. Atomic temperatures were measured by excited state population ratios (inferred from peak heights) for near-uv emission and compared to two-color pyrometry. Post detonation pressure was found by measuring the peak widths of atomic aluminum lines and comparing to those in a traditional, invasive, piezoelectric pressure gauge. [Preview Abstract] |
Wednesday, June 27, 2007 9:00AM - 9:15AM |
L5.00004: Analysis of Temperature Measurement at Lead/LiF Interface Under Shock Wave Compression Camille Chauvin, Pierre-Louis Hereil The results of pyrometric measurements performed at the interface of a lead target with a LiF window material are presented for stresses about 12 GPa. The purpose of the study is to analyze the part of the interface in the temperature measurement by a multi-channel infrared pyrometric device. The results show that the use of a specific deposite layer at the measured surface increases the emissivity of this surface. This leads to a better knowledge of the real temperature in the target by reducing the temperature error. A maximum value of 510 K has been measured for interface temperature. This is consistent with the behavior of lead under shock wave compression. Furthermore, the whole profile of measured temperature at the lead/LiF interface is also consistent which numerical simulation. [Preview Abstract] |
Wednesday, June 27, 2007 9:15AM - 9:30AM |
L5.00005: Time-Resolved Optical Measurements of Detonation and Combustion Products Joel Carney, John Wilkinson, James Lightstone This presentation exhibits our initial attempts at measuring detonation and combustion products using time-resolved absorption spectroscopy. Transient species in the post-detonation combustion environment of a fuel-rich explosive event include emissive and non-emissive products ranging in size from atomic to macroscopic. The time-resolved concentrations of emissive and non-emissive species relate to the overall efficiency of the detonation. Recently, our group has used streak-camera based time-resolved emission spectroscopy to directly measure the relative concentrations of emissive species in a detonation environment. To relate measured emission intensities to a total species concentration vs. time in the environment following a detonation, the ratio of emissive and non-emissive species need to be estimated. In this presentation, we compare concentrations of post-detonation combustion transient species (aluminum and aluminum monoxide) measured by time-resolved emission spectroscopy and time-resolved absorption spectroscopy. Pressed samples of PETN and aluminum are used as controlled, fuel-rich explosive mixtures. The absorption measurements are directly proportional to the transient concentration and serve to scale the relative emission measurement to the total (emissive + non-emissive) concentration. [Preview Abstract] |
Wednesday, June 27, 2007 9:30AM - 9:45AM |
L5.00006: Characterization and use of a CO$_{2}$ infrared laser for ignition of explosives Jeremy Monat, Edward Tersine, Brent Morgan, Peter Ostrowski This abstract reports on the characterization and use of a 200W, 10.6 $\mu $m CO$_{2}$ laser for nonresonant ignition of explosives. To characterize the laser, we measured its risetime with a detector whose response time is approximately 125 ns. We also measured the beam's spatial profile with a scanning pinhole setup. Next, we used the laser for testing of explosives for fundamental research and CAD/PAD (cartridge-actuated devices/propellant actuated devices) applications. Specifically, we determined energy-to-ignition values for TNT (2,4,6-trinitrotoluene) and the novel primary KDNP (4,6-dinitro-7-hydroxybenzofuroxan). Ignition was judged to begin at first light, which occurs when the laser-induced reaction first emits light as detected by a visible photodiode. To determine the energy to ignition accurately, we corrected the laser power for reflections. We used a high-speed camera to monitor the reaction progress from ignition to explosive consumption. [Preview Abstract] |
Wednesday, June 27, 2007 9:45AM - 10:00AM |
L5.00007: Time-Resolved Spectroscopic Measurements of Aluminum Oxidation in a Laser Ablation Event James Lightstone, Joel Carney Laser ablation of an aluminum sheet is used to create a high pressure and temperature environment for the investigation of aluminum (Al) oxidation. High energy pulsed lasers are used to initiate the ablation and to probe oxidation products in the expanding plume as a function of time and space. Emission, absorption, and scattering spectroscopies are used to deduce information on the observed reaction pathways, species concentrations, and internal energies. Emission measurements using a streak camera with 0.1 nm spectral resolution exhibit the line profiles of atomic Al and aluminum monoxide (AlO), which are sensitive to excited state populations and internal energy distributions. Analogous ground state information is recorded using absorption (laser induced fluorescence) spectroscopy. In general, comparable emission and absorption results for AlO imply a level of equilibrium within the expansion. Results from these studies will be presented along with progress toward adapting optical scattering (Raman) spectroscopies to identify additional aluminum oxide species formed in the ablation plume. The application of the spectroscopic techniques presented toward the measurement of a dynamic chemical process such as a detonating fuel-rich explosive formulation will also be discussed. [Preview Abstract] |
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