Bulletin of the American Physical Society
Joint Spring 2010 Meeting of the Texas Sections of the APS, AAPT, and SPS
Volume 55, Number 3
Thursday–Saturday, March 18–20, 2010; Austin, Texas
Session C1: Poster Session (10:00AM-12:00PM) |
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Room: Robert Lee Moore Hall 5th Floor Hallway |
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C1.00001: Radiation of spin waves from the open end of a microscopic magnetic-film waveguide Daniel Birt, Vladislav Demidov, Sergej Demokritov, Brian O'Gorman, Maxim Tsoi, Xiaoqin Li We have studied experimentally the radiation of spin waves from a permalloy-film microwaveguide into a continuous permalloy film. We show that due to a strong mismatch of the spin-wave spectrum caused by a variation in the demagnetizing field at the interface between the waveguide and the film, a frequency interval exists, where spin waves experience total reflection from the junction penetrating into the permalloy film in a tunnelinglike manner. At frequencies above this interval, complex frequency-dependent radiation patterns were observed characterized by a preferential radiation direction appearing due to the intrinsic anisotropy of the spin-wave dispersion characteristics in the film. [Preview Abstract] |
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C1.00002: Elastic Properties of Silicon Carbide Nanowires and Nanosize Grains up to 75 GPa T.W. Zerda Silicon carbide nanowires of average diameter of 30 nm and narrow size distribution were sintered from carbon nanotubes and silicon at 1200$^{\circ}$C. X-ray diffraction measurements of those SiC nanowires were conducted in a diamond anvil cell at room temperature and pressures up to 55 GPa applied by an alcohol medium. We used the same technique to study SiC grains of various sizes. The pressure-dependent volumes of the respective unit cells were calculated from the diffraction data, and the bulk moduli extracted from these studies depended on the particle size: 260 GPa for the 20 nm grains, 198 GPa for the 50 nm grains, and 193 GPa for the 130 nm grains. The bulk modulus of the 30 nm SiC nanowire was found to be 240 GPa. The bulk modulus study was extended to 75 GPa of pressure by use of a diamond anvil cell cryogenically loaded with an argon pressure medium. The bulk modulus was unchanged in this extended pressure range. The elevated bulk modulus of 20 nm grains is explained by the core-shell model developed by Palosz, \textit{et al}. The core atoms exhibit all the properties associated with the bulk material, but the interatomic distances of shell atoms may differ. With nano-sized materials, a much larger percentage of the constituent atoms belong to the shell. [Preview Abstract] |
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C1.00003: ABSTRACT WITHDRAWN |
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C1.00004: Spectroscopic second-harmonic generation and reflectance-anisotropy spectroscopy on reconstructed stepped Si(001) surfaces Robert Ehlert, Loucas Loumakos, Michael C. Downer Spectroscopic second-harmonic generation (SHG) and reflectance-anisotropy spectroscopy (RAS) are the two dominant non-invasive optical probes of electronic structure and chemical dynamics at surfaces, but underlying connections between these spectroscopies remain poorly understood. Here we combine spectroscopic SHG and RAS to characterize stepped Si(001) surfaces offcut toward [110]. Both the linear and nonlinear optical response of the clean surface are dominated by the large number of dangling bonds at the D$_B$ steps and reconstructed terraces. Selective adsorption of H$_2$ at step edges and/or terraces allows us to isolate individual contributions and by using a simplified bond hyperpolarizability model (SBHM) identify their common microscopic origin. This ability to monitor surface chemistry on stepped silicon surfaces enables us to develop these methods as non-invasive, in-situ sensors to guide and interpret self-directed growth of nanoscale structures. [Preview Abstract] |
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C1.00005: Femtosecond dynamics of cluster expansion Xiaohui Gao, Xiaoming Wang, Bonggu Shim, Alexey Arefiev, Mikhail Tushentsov, Boris Breizman, Mike Downer Noble gas clusters irradiated by intense ultrafast laser expand quickly and become typical plasma in picosecond time scale. During the expansion, the clustered plasma demonstrates unique optical properties such as strong absorption and positive contribution to the refractive index. Here we studied cluster expansion dynamics by fs-time-resolved refractive index and absorption measurements in cluster gas jets after ionization and heating by an intense pump pulse. The refractive index measured by frequency domain interferometry (FDI) shows the transient positive peak of refractive index due to clustered plasma. By separating it from the negative contribution of the monomer plasma, we are able to determine the cluster fraction. The absorption measured by a delayed probe shows the contribution from clusters of various sizes. The plasma resonances in the cluster explain the enhancement of the absorption in our isothermal expanding cluster model. The cluster size distribution can be determined. A complete understanding of the femtosecond dynamics of cluster expansion is essential in the accurate interpretation and control of laser-cluster experiments such as phase-matched harmonic generation in cluster medium. [Preview Abstract] |
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C1.00006: Hot carrier injection from angstrom-scale silicon-on-insulator films measured by optical second-harmonic generation Ming Lei, Jimmy Price, Michael Downer Internal multi-photon photoemission (IMPE) and time-dependent electrostatic field-induced second-harmonic (TD-EFISH) generation are used to probe injection of hot electrons from silicon-on-insulator (SOI) films as thin as 20 angstroms (2 nm) into an overlying gate oxide and an underlying buried oxide (BOX). Photo-excited electrons are found to inject into both native gate and buried thermal oxides at different rates, including changes of opposite sign in the TD-EFISH signal, whereby they are distinguished straightforwardly. Techniques are demonstrated to measure kinetics of the two injection processes independently of each other and of competing charge injection at the substrate/BOX interface, enabling extraction of quantitative charge injection kinetic parameters for each SOI/oxide interface. The results demonstrate that optical SHG can non-invasively and quantitatively characterize hot carrier injection from ultrathin SOI --- a key determinant of SOI device reliability and lifetime --- without device fabrication. [Preview Abstract] |
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C1.00007: Spectroscopic SHG and spectroscopic ellipsometry study of silicon nanocrystals embedded in SiO$_{2}$ Junwei Wei, Adrian Wirth, Michael Downer The light-emitting silicon nanocrystals (Si NCs) embedded in silica matrix open up the possibility for silicon photonics. Optical spectroscopy can help elucidate unique, but poorly understood, bonding structures at the nano-interfaces that are responsible for the efficient photoluminescence. Here we present SHG amplitude and phase spectra of a 1$\mu$m-thick layer of 3 nm $\pm$ 30{\%} diameter Si NCs prepared by implanting Si ions into SiO$_{2}$ then annealing in Ar or H$_{2}$/Ar mixture at 1100$^{\circ}$C using cross-polarized two-beam second-harmonic generation (XP2-SHG). We also measure the linear dielectric function of the NC layer using spectroscopic ellipsometry (SE). The linear spectra show a significant reduction in the dielectric functions in Si NCs compared to bulk silicon. The pronounced E$_{2}$ critical point transition peak is somewhat blueshifted to the bulk E$_{2}$ peak while E$_{1}$ transition is strongly suppressed. The SHG spectra are only slightly perturbed by annealing in hydrogen. A fit of the SHG amplitude and phase spectra using model resonance functions yields resonances different from the linear spectra. A model with an intermediate transition layer of variable composition between the Si NC core and the amorphous SiO$_{2}$ matrix is introduced to explain the linear and SHG spectra. [Preview Abstract] |
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C1.00008: Chirped pulse Raman amplifier for two-color high-intensity laser-plasma experiments James ``JC" Sanders, Franklin Grigsby, Rafal Zgadzaj, Michael Downer The interactions of high-intensity lasers with a plasma are troubled by instabilities. A two-color laser pulse can be used to control these instabilities, but the intensities necessary to do this require that both colors have powers on the order of terawatts. Here, we present a scheme for generating terawatt, two-color laser pulses by using a three-stage amplifier system based on the stimulated Raman scattering of a chirped pulse. The first two stages consist of a Raman-shifter and a Raman-amplifier---two barium nitrate crystals---which works by first Stokes'-scattering a low-energy seed in the first crystal and then amplifying the seed via four-wave mixing to a few millijoules in the second crystal. The amplified first Stokes' pulse is then to be further amplified by a conventional Ti:Sapph crystal in a 6-pass bowtie configuration. The amplified beam has a peak wavelength of 873 nm and is to be compressed to the bandwidth limit ($\sim $50 fs). It will then be re-combined with a conventionally generated TW laser centered at 800 nm and will be sent into the plasma. [Preview Abstract] |
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C1.00009: The dynamics of quasibound state formation in the driven Gaussian potential Kyungsun Na, Daungruthai Jarukanont, Linda Reichl The quasibound states of a particle in an inverted-Gaussian potential interacting with an intense laser field are studied using complex coordinate scaling and Floquet theory. The dynamics of the driven system is different depending on whether the driving field frequency is less than or greater than the ionization frequency. As the laser field strength is increased, a new quasibound state emerges as the result of a pitchfork bifurcation in the classical phase space. Changes in the time-averaged ``dressed potential'' appear related to this bifurcation and provide additional confirmation of the role of the bifurcation on the emergence of a new quasibound state. The Husimi plots of the quasibound state residues reveal strong support on the periodic orbits of the bifurcation at frequencies above the ionization frequency. [Preview Abstract] |
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C1.00010: Inner-shell photodetachment of C$_{60}^-$ R.C. Bilodeau, N. Berrah, S. Schippers, A. Muller, D.A. Esteves, R.A. Phaneuf, N.D. Gibson, C.W. Walter, A. Aguilar First photodetachment spectroscopy on negative ions of C$_{60}$ has been conducted, using the merged ion-photon beam apparatus at the ALS with photon energies from 20eV up to 320eV. Multiple electron ejection was substantial at all photon energies, allowing product charge states up to 3+ to be measured. Fragmentation into cations of C$_{58}$, and C$_{56}$, was also studied. The relative strengths of the 7 observed product channels and absolute cross sections were measured at selected energies in this range. We find some structure that differs significantly from previous results in photoionization experiments on C$_{60}$ cations [S.W. J. Scully {\it et al.}, Phys. Rev. Lett. {\bf 94}, 065503 (2005).]. [Preview Abstract] |
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C1.00011: Production of exotic atoms at the Large Hadron Collider at CERN Mark Ellerman, Carlos Bertulani We study the production of exotic atoms in ultraperipheral pp and heavy ion collisions at the Large Hadron Collider (LHC) at CERN. Our calculations apply to the production of muonic atoms, pionic atoms, protonium, and other exotic atoms. The space-time distribution of the produced pairs is investigated in detail. [Preview Abstract] |
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C1.00012: Phase measurements on a subwavelength optical metamaterial based on metallic paired strips Travis Autry, Kara Maller, Thomas Jarvis, Xiaoqin Li, Dimitriy Korobkin, Gennady Shvets, Marcelo Davanco, Xuhuai Zhang, Stephen Forrest There are no known naturally occurring material with negative index of refraction due to the fact that the electrical resonances and the magnetic resonances don't overlap in frequency. However, artificially engineered materials, known as metamaterials, can be designed to exhibit such peculiar properties. We study a subwavelength optical metamaterial composed of paired gold strips separated by continuous gold film. According to theoretical calculations, this structure is expected to display a negative index of refraction in the near-infrared. We have performed phase measurements of the material using a polarization interferometer in the range of 750-960 nm using a Ti: Sapphire laser. We are in the process of extending the measurement to a longer wavelength range using a supercontinuum. The phase information of the transmitted and reflected wave at various wavelengths is critical for characterizing the index of refraction. [Preview Abstract] |
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C1.00013: Environmental Radiation Studies Utilizing RadNet Steven Jackson RadNet is an Environmental Protection Agency (EPA) managed environmental radiation and air quality monitoring station that has been recently installed on the Angelo State University campus. RadNet cycles air through a filter which collects particulate matter for an examination of alpha and beta activities of contained material. This project includes defining dominant alpha and beta emitters in the local environment, conducting a correlation study involving the effect of weather and wind direction on filter activity, physical interpretation of air quality index (AQI), and the use of X-ray fluorescence to verify radon decay progeny in the local environment. [Preview Abstract] |
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C1.00014: Python Graphical User Interface (GUI) for Control of the Levitated Dipole Experiment David Jacome, Darren Garnier, Paul Woskov, Jay Kesner The Levitated Dipole Experiment (LDX) is used to study the confinement properties of plasmas in a magnetic dipole field. In LDX a superconducting coil is levitated for up to 3 hours within a large vacuum chamber to produce the confining dipole field. The plasma experiments take place during this time, with $\sim$10 second plasma shots, one shot every $\sim$5 min. MDSplus software is used to run the experiment and store the data. The software is currently controlled by command line operations. Since levitation time is limited, it's important to maximize efficiency and accuracy of experimental operations. Here, we present a Graphical User Interface (GUI) to efficiently control the operation of the experiment. The need for a GUI that integrates the MDSplus data cycle, cell access control, and routine experimental parameter controls is necessary. The GUI program provides a simple method for monitoring and setting experiment parameters. Python is used as the primary language to run the commands. A program called XRCed distributed by wxPython works as a visual tool. [Preview Abstract] |
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