Bulletin of the American Physical Society
APS March Meeting 2016
Volume 61, Number 2
Monday–Friday, March 14–18, 2016; Baltimore, Maryland
Session C46: Instrumentation II: Spectroscopy |
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Sponsoring Units: GIMS Chair: Angela Hight-Walker, NIST Room: 311 |
Monday, March 14, 2016 2:30PM - 2:42PM |
C46.00001: Temperature Controlling Digital Cameras for Time-Resolved Angle-Resolved Photoemission Spectroscopy Alexander Nguyen, Gregory Affeldt, Kenneth Gotlieb, Alessandra Lanzara Angle-resolved photoemission spectroscopy experiments (ARPES) use charged couple device (CCD) detectors to measure the spectra of various material. A CCD measures the number of photons that hit it; a problem with CCDs is that thermal energy can create false photon counts. By building a temperature controller the CCD's temperature is lowered to reduce the number of false counts, similarly, the temperature controller keeps the temperature stable reducing the randomness in false counts. [Preview Abstract] |
Monday, March 14, 2016 2:42PM - 2:54PM |
C46.00002: Towards Laser-based Angle-Resolved Photoemission Spectroscopy at Ultralow Temperatures Tejas Deshpande, John Harter, Alexei Fedorov, David Hsieh Recent technical advances in angle-resolved photoemission spectroscopy (ARPES) have enabled electronic structures of solids to be mapped at sub-Kelvin temperatures [1] or with sub-meV energy resolution [2]. However, achieving both conditions simultaneously remains an ongoing effort in the ARPES community. To this end, we discuss our progress in employing a laser-based source to perform ARPES of novel materials at ultralow temperatures.\\ [1] Borisenko. \emph{Synchrotron Radiation News} \textbf{25}, no. 5 (2012): 6-11.\\ [2] Okazaki, \emph{et al.} \emph{Science} \textbf{337}, no. 6100 (2012): 1314-1317. [Preview Abstract] |
Monday, March 14, 2016 2:54PM - 3:06PM |
C46.00003: Positron spectroscopy of 2D materials using an advanced high intensity positron beam A MCDONALD, V CHIRAYATH, Z LIM, R GLADEN, M CHRYSLER, A FAIRCHILD, A KOYMEN, A WEISS An advanced high intensity variable energy positron beam(\textasciitilde 1eV to 20keV) has been designed, tested and utilized for the first coincidence Doppler broadening (CDB) measurements on 6-8 layers graphene on polycrystalline Cu sample. The system is capable of simultaneous Positron annihilation induced Auger electron Spectroscopy (PAES) and CDB measurements giving it unparalleled sensitivity to chemical structure at external surfaces, interfaces and internal pore surfaces. The system has a 3m flight path up to a micro channel plate (MCP) for the Auger electrons emitted from the sample. This gives a superior energy resolution for PAES. A solid rare gas(Neon) moderator was used for the generation of the monoenergetic positron beam. The positrons were successfully transported to the sample chamber using axial magnetic field generated with a series of Helmholtz coils. We will discuss the PAES and coincidence Doppler broadening measurements on graphene --Cu sample and present an analysis of the gamma spectra which indicates that a fraction of the positrons implanted at energies 7-60eV can become trapped at the graphene/metal interface. [Preview Abstract] |
Monday, March 14, 2016 3:06PM - 3:18PM |
C46.00004: Stimulated Resonant X-Ray Emission in Solids Zhao Chen, Daniel Higley, Markus Hantschmann, Virat Mehta, Martin Beye, William Schlotter, Joachim Stohr We present direct evidence of resonant stimulated X-Ray emission in magnetically patterned Co/Pd multilayers. At a free electron laser, we measure X-Ray transmission through Co/Pd of ultrafast ($\approx$2fs) X-Ray pulses at the Co $L_3$ edge for fluences of up to 2 J/cm$^2$/fs simultaneously in the transmission and scattering geometries. With increasing fluence, we observe a nonlinear decrease in first-order scattering intensity together with a compensating increase in transmitted forward intensity for all energies within the Co resonant absorption edge. At high enough fluences ($>$1 J/cm$^2$/fs), the sample absorption spectrum and scattering intensity are both suppressed by over two orders of magnitude, leaving the sample effectively transparent to X-Rays. In our geometry, these two effects are indicative of elastic stimulated scattering, which favors forward transmission at the cost of scattered intensity in all other directions. We then show that our data is well-described by stimulated emission calculations using the optical Bloch equations. Our dual measurement serves as a pioneering study of X-Ray stimulated processes, and paves the way for experiments on realizing potentially powerful X-Ray spectroscopic techniques such as stimulated RIXS. [Preview Abstract] |
Monday, March 14, 2016 3:18PM - 3:30PM |
C46.00005: Extreme-ultraviolet ultrafast ARPES at high repetition rates Jan Buss, He Wang, Yiming Xu, Sebastian Stoll, Lingkun Zeng, Stefan Ulonska, Jonathan Denlinger, Zahid Hussain, Chris Jozwiak, Alessandra Lanzara, Robert Kaindl Time- and angle-resolved photoemission spectroscopy (trARPES) represents a powerful approach to resolve the electronic structure and quasiparticle dynamics in complex materials, yet is often limited in either momentum space (incident photon energy), probe sensitivity (pulse repetition rate), or energy resolution. We demonstrate a novel table-top trARPES setup that combines a bright 50-kHz source of narrowband, extreme ultraviolet (XUV) pulses at 22.3 eV with UHV photoemission instrumentation to sensitively access dynamics for a large momentum space. The output of a high-power Ti:sapphire amplifier is split to provide the XUV probe and intense photoexcitation (up to mJ/cm$^{\mathrm{2}})$. A vacuum beamline delivers spectral and flux characterization, differential pumping, as well as XUV beam steering and toroidal refocusing onto the sample with high incident flux of 3x10$^{\mathrm{11}}$ ph/s. Photoemission studies are carried out in a customized UHV chamber equipped with a hemispherical analyzer (R4000), six-axis sample cryostat, and side chambers for sample loading, storage and preparation. An ARPES energy resolution down to 70 meV with the direct XUV output is demonstrated. We will discuss initial applications of this setup including Fermi surface mapping and trARPES of complex materials. [Preview Abstract] |
(Author Not Attending)
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C46.00006: Role of Spatial Chirp in High Harmonic Extreme Ultraviolet (XUV) Absorption Spectroscopy of Thin Films Ming-Fu Lin XUV light from high harmonic generation is an emerging new tool for studying ultrafast dynamics. Such sources have intrinsic ``spatial chirp'' that can cause significant periodic artifacts in absorption spectra of inhomogeneous samples. We show that a uniform thin-film morphology is required in order to obtain harmonic-structure free absorption spectra, especially for organometallic complexes that have strong non-resonant absorption features from the organic ligands. Demonstration of several static absorption spectra of different organometallic complexes and perovskite materials reveals elemental, oxidation state, and band structure specificity in agreement with theoretical results. [Preview Abstract] |
Monday, March 14, 2016 3:42PM - 3:54PM |
C46.00007: High Power Terahertz Fields Generated by an Arrayed Photoconductive Antenna Structure Benjamin Graber, Dong Ho Wu, Christopher Kim Terahertz spectroscopy has a wide array of scientific, commercial, and industrial applications. However, to date, terahertz signal strength of available commercial systems is limited to less than 100 uW in average terahertz power. It is expected that with enhanced terahertz power one may be able to obtain better terahertz spectral information, and enable more practical terahertz applications in real environments. In order to achieve this goal we experimentally constructed an arrayed photoconductive antenna structure, in which terahertz signals from a few photoconductive antennas are combined by adjusting every terahertz signals to be in phase. The collected signals from the multiple emitters are concentrated onto a small area so that the combined terahertz signal strength is over 1mW in average power and peak electric field over 16kV/m. The terahertz frequency spectrum of combined signals is unaltered and exactly the same as that of each individual photoconductive antenna, which spans from 100GHz to 3THz. Experimental details regarding power measurement, time domain signals, and frequency spectra analysis will be discussed. This prototype array structure appears to scale linearly with the addition of photoconductive antennas. [Preview Abstract] |
Monday, March 14, 2016 3:54PM - 4:06PM |
C46.00008: Terahertz nano-spectroscopy and imaging of super?uid surface plasmons in conventional and anisotropic superconductors H. T. Stinson, J. S. Wu, B. Y. Jiang, Z. Fei, A. S. Rodin, B. Chapler, A. S. Mcleod, A. Castro Neto, Y. S. Lee, M. M. Fogler, D. N. Basov We numerically model near-field spectroscopy and superfluid polariton imaging experiments on conventional and unconventional superconductors in the infrared and terahertz regime. Our modeling shows that near-field spectroscopy can measure the magnitude of the superconducting gap in Bardeen-Cooper-Schrieffer superconductors with nanoscale spatial resolution. We demonstrate how the same technique can measure the $c$-axis plasma frequency, and thus the $c$-axis superfluid density, of layered unconventional superconductors such as cuprates and pnictides with identical spatial resolution. We discuss the development of a cryogenic terahertz near-field microscope designed to perform these proposed experiments, and recent proof of principle results at room temperature. [Preview Abstract] |
Monday, March 14, 2016 4:06PM - 4:18PM |
C46.00009: Inkjet Printed Wire-Grid Polarizers for the THz Frequency Range A. Farid, N. J. Laurita, B. Tehrani, J. Hester, M. M. Tentzeris, N. P. Armitage We have investigated the use of inkjet printing technology for the production of THz range wire-grid polarizers using time-domain terahertz spectroscopy. Such technology affords a cheap and reproducible way of quickly manufacturing THz range metamaterial structures. Thin silver-nanoparticle ink lines were printed using a Dimatix DMP-2831 printer. We investigated the optimal printing geometry of the polarizers by looking at a number of samples with printed wires of varying thickness and spacing. We also investigate the ultimate capabilities of these polarizers by investigating their properties when stacked. [Preview Abstract] |
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