Bulletin of the American Physical Society
17th Biennial International Conference of the APS Topical Group on Shock Compression of Condensed Matter
Volume 56, Number 6
Sunday–Friday, June 26–July 1 2011; Chicago, Illinois
Session B5: Spectroscopy and Optical Studies I |
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Chair: Cindy Bolme, Los Alamos National Laboratory Room: Renaissance Ballroom D |
Monday, June 27, 2011 9:15AM - 9:30AM |
B5.00001: Free carrier lifetime reduction in shock-compressed GaAs Paulius Grivickas, Matthew McCluskey, Yogendra Gupta Understanding the changes in dynamic carrier properties, including lifetime, are important for operation of gallium arsenide (GaAs) based optoelectronic devices. Significant carrier lifetime reductions were determined in GaAs:Te, shock-compressed along [100] to 4 GPa, using time- and spectrally-resolved photoluminescence (PL) measurements. Lifetime changes were extracted from PL signals extending over five orders of magnitude following a short excitation pulse in single event shock experiments. Several time-resolved recombination mechanisms showed a linear lifetime reduction in marked contrast to earlier hydrostatic pressure results. The present results suggest that the lifetime reaches a minimum at the direct-to-indirect band gap transition. [Preview Abstract] |
Monday, June 27, 2011 9:30AM - 9:45AM |
B5.00002: Self-emission spectroscopy of single crystal quartz Minta Akin, Ricky Chau, Neil Holmes We report the self-emission spectra of single crystal quartz from 200-800 nm under stress up to about 1 Mbar. These spectra show the presence of several narrow peaks, in contrast to the broad luminescent peaks more often observed. We hope to use these spectra to elucidate the phenomena, such as defect formation, occurring during shock. [Preview Abstract] |
Monday, June 27, 2011 9:45AM - 10:00AM |
B5.00003: Anisotropic direct-to-indirect band gap transition in shock- and ramp-wave compressed GaAs M.D. McCluskey, P. Grivickas, Y.M. Gupta Gallium arsenide (GaAs) is an important material for laser diodes, light emitting devices, and high-speed electronics. Strain-induced electronic band structure changes affect the performance of multi-layered GaAs-based devices. In the present work, effects of uniaxial strain on the low-temperature photoluminescence of GaAs were investigated using shock and ramp wave compression along the [100], [111], and [100] orientations. Uniaxial strain transformed GaAs from a direct-gap to an indirect-gap semiconductor, dramatically altering its optical properties. Unlike hydrostatic pressure, uniaxial strain along [111] produces a large splitting of the $L$ band. This causes the $L$-band minimum to plunge downward, resulting in a novel ``$L$-gap'' semiconductor. [Preview Abstract] |
Monday, June 27, 2011 10:00AM - 10:15AM |
B5.00004: The elastic-plastic response of metal films subjected to ultrafast laser-generated shocks Von Whitley, Shawn McGrane, Cynthia Bolme, David Moore We have measured the free-surface response of metal films with nominal thicknesses ranging from 500 nm to 8 $\mu$m to shocks generated from chirped ultrafast lasers. We launch a single laser generated stress wave into the metal film, but measure two stress waves on the free surface separated in time. The two waves correspond to the elastic and plastic response of the thin metal films. Using ultrafast dynamic ellipsometry, we have measured the separation of the elastic and plastic waves to times as short as 20 picoseconds and measured peak elastic free surface velocities as high as 1.4 km/s in aluminum. We will discuss the experimental results we have measured for aluminum, copper and other metals. [Preview Abstract] |
Monday, June 27, 2011 10:15AM - 10:30AM |
B5.00005: Nitro Stretch Probing of a Single Molecular Layer to Monitor Shock Compression with Picosecond Time-Resolution Christopher Berg, Alexei Lagutchev, Yuanxi Fu, Dana Dlott To obtain maximum possible temporal resolution, laser-driven shock compression of a molecular monolayer was studied using vibrational spectroscopy. The stretching transitions of nitro groups bound to aromatic rings was monitored using a nonlinear coherent infrared spectroscopy termed sum-frequency generation, which produced high-quality signals from this very thin layer. To overcome the shock opacity problem, a novel polymer overcoat method allowed us to make the observation window (witness plate) a few micrometers thick. The high signal-to-noise ratios ($>$100:1) obtained via this spectroscopy allowed us to study detailed behavior of the shocked molecules. To help interpret these vibrational spectra, additional spectra were obtained under conditions of static pressures up to 10 GPa and static temperatures up to 1000 \r{ }C. Consequently, this experiment represents a significant step in resolving molecular dynamics during shock compression and unloading with both high spatial and temporal resolution. [Preview Abstract] |
Monday, June 27, 2011 10:30AM - 10:45AM |
B5.00006: Surface chemical reaction of laser ablated aluminum sample for detonation initiation Jack Yoh, Chang-hwan Kim, Ardian Gojani We explore the evolution of metal plasma generated by high laser irradiances and its effect on the surrounding air by using shadowgraph images after laser pulse termination; hence the formation of laser supported detonation and combustion processes has been investigated. The essence of the paper is in observing initiation of chemical reaction between ablated aluminum plasma and oxygen from air by inducing high power laser pulse ($>$1000 mJ/pulse) and conduct a quantitative comparison of chemically reactive laser initiated waves with the classical detonation of exploding aluminum (dust) cloud in air. Findings in this work may lead to a new method of initiating detonation from metal sample in its bulk form without the need of mixing nano-particles with oxygen for initiation. [Preview Abstract] |
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