Bulletin of the American Physical Society
75th Annual Meeting of the Southeastern Section of APS
Volume 53, Number 13
Thursday–Saturday, October 30–November 1 2008; Raleigh, North Carolina
Session PA: Applied Physics II |
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Chair: Mohan Aggarwal, Alabama A&T University Room: Holiday Inn Brownstone Roosevelt |
Saturday, November 1, 2008 10:30AM - 10:42AM |
PA.00001: Bifurcations and Averaging in a Series Array of Tunnel Diodes Kevin J. Brown, Huidong Xu, Stephen W. Teitsworth We investigate nonlinear electrical conduction properties of a series array of tunnel diodes using both numerical simulation and experimental measurement. Tunnel diodes are negative differential resistance (NDR) circuit elements and, in a series configuration, they provide a useful model system for nonlinear transport in more complex electronic structures such as semiconductor superlattices [1]. Measurements reveal high-frequency (of order 1 GHz), small-amplitude oscillations in the current when the diodes are voltage-biased in the NDR region. For a system of $N$ diodes, these fast oscillations are associated with Hopf bifurcations in a $3N$-dimensional nonlinear circuit model that includes intrinsic reactances for each diode. A nonlinear averaging method is applied to the full model, allowing the elimination of fast time scale behavior, and results in a reduced dynamical system of dimension $N$. Simulations of the reduced model are found to accurately describe the experimental circuit behavior on time scales that are much greater than the oscillatory time scale. [1] H. Xu and S. W. Teitsworth, Phys. Rev. B {\bf 76}, 235302 (2007). [Preview Abstract] |
Saturday, November 1, 2008 10:42AM - 10:54AM |
PA.00002: Infrared absorption and emission studies of Er:YAG, Er:KPb$_{2}$Cl$_{5}$, and Er:KPb$_{2}$Br$_{5}$ for eye-safe laser applications Craig Hanley, Ei Brown, Uwe Hommerich, Sudhir Trivedi, John Zavada There exists a significant current interest in the development of a new generation of 1.5-1.6$\mu $m eye-safe solid-state lasers with resonance diode laser pumping. Applications of laser sources that operate in the eye-safe wavelength regime near 1.5-1.6$\mu $m include remote sensing, long distance telemetry, and optical communications. Eye-safe laser wavelengths can be achieved by using trivalent Er$^{3+}$, which has an emission transition at $\sim $1.5$\mu $m. Prior to the development of resonantly pumped erbium lasers, two approaches were employed for eye-safe lasers, Nd-based lasers driving nonlinear optical parametric oscillators and erbium-doped glass lasers. System complexity and heat management limits the power scaling of these two approaches. The availability of new diode-pumped sources operating at $\sim $1.45$\mu $m has made resonantly pumped Er$^{3+}$ lasers a viable choice for high-power eye-safe lasers. Crystalline Er:YAG is currently the main gain material under consideration for 1.5$\mu $m Er lasers. In this work we present spectroscopic results of ceramic Er:YAG, Er:KPb$_{2}$Cl$_{5}$, and Er:KPb$_{2}$Br$_{5}$. Infrared absorption and emission cross-sections were analyzed and evaluated for potential applications as 1.5$\mu $m gain media. [Preview Abstract] |
Saturday, November 1, 2008 10:54AM - 11:06AM |
PA.00003: Growth and spectroscopic characterization of Ho-doped KPb$_{2}$Cl$_{5}$ crystal for mid-IR laser applications Olusola Oyebola, Ei Brown, Uwe Hommerich, Sudhir Trivedi, Althea Bluiett, John Zavada Results of the crystal growth and infrared spectroscopy of Ho:KPb$_{2}$Cl$_{5}$ (KPC) are presented for possible applications in mid-infrared solid-state lasers. KPC was synthesized from high purity PbCl$_{2}$ and KCl materials and purified through horizontal zone-refinement. 1-3 wt{\%} of HoCl$_{3}$ was mixed to the purified KPC and molten under a chlorinating atmosphere. Ho: KPC crystals were then grown using a self-seeded horizontal Bridgman technique. Absorption and emission studies were carried out on the polished crystal. Following optical excitation at 750 nm and 885 nm, several emission bands were observed in the near- and mid-IR spectral region. Further spectroscopic studies were focused on the mid-IR emission at 3900 nm arising from the Ho$^{3+}$ transition $^{5}$I$_{5} \rightarrow ^{5}$I$_{6}$. The room temperature emission lifetime of the $^{5}$I$_{5}$ level was measured to be 4.9 ms, which is in good agreement with the radiative lifetime determined from a Judd-Ofelt analysis. This result indicates that multi-phonon relaxation processes are not significant for the 3.9 $\mu $m emission from Ho: KPC. Further results of the infrared absorption and emission properties of Ho: KPC will be presented at the conference. [Preview Abstract] |
Saturday, November 1, 2008 11:06AM - 11:18AM |
PA.00004: Theory of single nuclear spin detection in magnetic resonance force microscopy Srinivasa Chemudupati, Vladimir Tsifrinovich We develop a theory for the measurement of a nuclear spin state in a paramagnetic atom with Oscillating Cantilever-Driven Adiabatic Reversals (OSCAR) in Magnetic Resonance Force Microscopy (MRFM). In this theory, we use a semi-classical approach where the electron-nuclear spin system, with hyperfine interaction, is treated quantum mechanically and the motion of the ferromagnetic particle on the cantilever tip is treated classically. Our computations support the idea of the measurement of a nuclear spin state by detection of a single electron spin. [Preview Abstract] |
Saturday, November 1, 2008 11:18AM - 11:30AM |
PA.00005: Optimizing extraction of information from resonance lines in Fourier-transform infrared spectroscopy P. Aggarwal, D.E. Aspnes The major analytic challenge in spectroscopy is to extract the maximum amount of information from an optical feature or features that are usually defined by a small number of data points.~ These in turn are often adversely influenced by both noise and the resolution function of the spectrometer. In dispersive-optical data the optimal approach for analyzing individual or closely spaced features is to Fourier-transform them and perform the analysis in reciprocal space, a procedure that requires the removal of endpoint-discontinuity artifacts.~ In Fourier-transform infrared spectroscopy (FTIR) the situation is more complicated in that the interferogram is measured and the spectrum calculated by Fourier analysis. We show that endpoint-discontinuity considerations provide insight into the effects of apodization on the Fourier transform of the interferogram.~ Once these effects are taken into account, individual structures can be analyzed as in the dispersive-optics case. [Preview Abstract] |
Saturday, November 1, 2008 11:30AM - 11:42AM |
PA.00006: Prolonging Electron Emission in Pyroelectric Crystal Accelerators Stephen Shafroth, Anya Derbakova, Vishal Rao, Kuai Yu Pyroelectric crystal accelerators have been used to accelerate electrons which produce X-rays on interacting with matter and are commercially available (Amptek). They have also been used to accelerate positive ions such as deuterons, which when colliding with deuterium targets produce nuclear fusion, giving rise to fast neutrons and protons. A problem with these crystal accelerators is that as the crystal temperature changes, particularly for fast temperature changes, the emission rate increases too fast and produces a discharge before the surface charge can build up sufficiently to accelerate ions or electrons to the highest energies. To address this problem we have developed LabView vi's which allow crystal heating rate and ambient pressure to be controlled. Electron emission has been recorded for about one hour without a discharge. [Preview Abstract] |
Saturday, November 1, 2008 11:42AM - 11:54AM |
PA.00007: Novel Pyroelectric Material Systems for Infrared Sensor Applications Padmaja Guggilla, Ashok Batra, Matthew Edwards Perovskite structured ceramics have been investigated due to their excellent dielectric, electro-optical, piezoelectric, and pyroelectric properties. Often dopants or additives are used in basic formulations of the materials to enhance or tune the material properties. Lead zirconate titanate (PZT), Cation(s) modified lead zirconate titanate such as lead lanthanum zirconate titanate (PLZT: lanthanum doped PZT), Mn doped lead lanthanum zirconate titanate (STPZT-2) and commercially available modified PZT (BM740) ceramics have been studied for their use in infrared detectors. Oxygen ions with 200 \textit{KeV} energy and doses of 1.0 $\times $ 10$^{16}$ \textit{ions/cm}$^{2}$ are irradiated onto BM 740 and its response is studied in terms of dielectric and pyroelectric properties before and after irradiation. As the pyroelectric materials' figure-of-merit depend upon the element size and the element thermal conductance, pyroelectric materials have also been examined in the form of thick film and thin film. Specified materials' figures-of-merit for their use in infrared detector are calculated and results are compared with several existing candidate materials. [Preview Abstract] |
Saturday, November 1, 2008 11:54AM - 12:06PM |
PA.00008: Investigation of locally favored structures in Al-La-Ni metallic glasses using $^{27}$Al NMR Spectroscopy Magdalena Sandor, Xuekui Xi, Yue Wu Al-TM-RE (TM= transition metal, RE = rare earth) bulk metallic glasses (BMGs) with high Al content have gained much research interest due to their high potential as structural and functional materials. The first recent fabrication of La$_{85-x}$Al$_{x}$Ni$_{15}$ (15 $\le $ x $\le $ 70) BMGs have inspired an NMR systematic study of their locally favored structures (LFSs). These BMGs are reported to show characteristics of high thermal stability, fragility, and considerable mechanical strength. $^{27}$Al NMR spectroscopy and nutation experiments are performed to unveil the sensitive structural dependence on line width and quadrupolar frequency with Al composition. It is observed that maximum glass forming ability (GFA) for this system prefers a decrease of symmetry at Al sites. Minimal GFA corresponding to instances of high symmetry occur in Al-rich and Al-poor regimes. These results, in addition to previous work, suggest that Ni and La atoms have unique local chemical and topological environments at different Al compositions. The monotonic decrease of relatively small $^{27}$Al Knight shifts with increasing Al concentration demonstrates the evolution of local electronic structure at Al sites. This study is valuable in correlating the unique role that TM and RE elements play in local compositional and geometrical order of high glass-forming Al-based BMGs. [Preview Abstract] |
Saturday, November 1, 2008 12:06PM - 12:18PM |
PA.00009: Effect of Preloading Condition on Fringe Pattern in Electronic Speckle Pattern Interferometry Tomohiro Sasaki, Sanichiro Yoshida, John Gaffney Electronic speckle pattern interferometry(ESPI) has received considerable attention as a measurement method capable of whole-field, dynamic analysis. In this study, an attempt is made to diagnose the degree of deformation based on the fringe patterns formed with an in-plane ESPI setup. We focus on the change in fringe pattern that preloaded specimens show when they are reloaded after released from the initial tensile load. If the degree of deformation can be identified from a specific change in the fringe pattern, this technique can be potentially used to predict material's remaining life. In this report, we discuss difference in the fringe pattern observed in Al-Mg alloy specimens preloaded to an under- and over-yield stress levels. In addition, difference in the fringe pattern based on the difference in Mg content is discussed. [Preview Abstract] |
Saturday, November 1, 2008 12:18PM - 12:30PM |
PA.00010: Can we know loading history of solid-state materials? Sanichiro Yoshida, John Gaffney, Tomohiro Sasaki, Christopher Schneider Using an optical interferometric technique called electronic speckle-pattern interferometry (ESPI) and a deformation theory called physical mesomechanics (PMM), an attempt is made to identify the loading history of aluminum specimens. The ESPI is used to form interferometric fringes representing in-plane displacement under tensile loading. PMM is used to interpret the obtained fringe patterns. Specimens preloaded to different degrees, ranging from a moderate elastic stage to late plastic stage, are reloaded within the elastic limit for multiple times. Fringe patterns resulting from each reloading cycle are classified in terms of the basic patterns, each representing longitudinal deformation, shear deformation, rotation, and their combinations. Specimens under the same preload/reload condition show a common feature in the transition of the classified patterns, whereas specimens under different preload/reload conditions show different transitions. Generally speaking, fringe patterns tend to show more rotational nature as deformation develops even in the reloading within the elastic limit. This result is consistent with PMM, which characterizes plastic deformation as shear instability leading to rotation. [Preview Abstract] |
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