Department of Physics & Astronomy Colloquia

May 4, 2015 Dr. Ariunbold Gombojav, Texas A&M University

Optimizing the laser-pulse configuration for ultrafast coherent Raman spectroscopy

Host: Dr. Chuji Wang

Abstract:

     Lasers have been widely used in biomedical and chemical research to study various properties of molecules. One example is the spontaneous Raman process, when light irradiates molecules the lower frequency light is emitted. This frequency shift is unique for each molecule to provide a “fingerprint” for species identification. Generally, the spontaneous Raman signal is weak. It can be enhanced by using one of the powerful techniques for molecular detection, coherent Raman spectroscopy based on Coherent Anti-Stokes Raman Scattering (CARS) process. Three pulses involved in this process. The two pulses coherently excite the molecular vibrations in unison. The third pulse scatters off these coherent oscillations generating a strong signal (anti-Stokes light). However, CARS signature is vastly ob-scured by non-resonant background contributions from other molecules pre-sent in the sample. A variety of methods used to counteract these back-ground vibrations have yielded only limited success.
     Femtosecond (one billionth of one millionth of a second) laser sys-tems in which the pulse energy is compressed within such a short time range and becomes extremely high put forward the potential improvement in CARS diagnostic capabilities.
     In this talk, a newly developed spectroscopic technique based on ultrafast coherent Raman scattering will be presented. The key advantage of this new technique is to substantially suppress the non-resonant background noise by shaping and delaying the third pulse, which probes the coherence of the medium that initially prepared by the two broadband pulses. We have experimentally demonstrated a robustness and superiority of signal-to-noise ratio of this developed technique, for instance, by identifying as few as 10000 bacterial spores at a single laser-shot level.
     Furthermore, I will discuss its potential technological transformation into a cost-effective (all-fiber) CARS device to be readily applied for envi-ronmental, agricultural and healthcare scientific research.

Key reference: Dmitry Pestov, Robert K. Murawski, Gombojav O. Ariunbold, et al., Opti-mizing the Laser-Pulse Configuration for Coherent Raman Spectroscopy, Science 316 265 (2007). [Highlights on photonics spectra], [Princeton Uni-versity news], [Science Daily], [A perspective given by Dr. Robert Lucht in SCIENCE Magazine]

April 28, 2015 Prof. Kevin Beach, University of Mississippi

Bonds, dimers, and loops in quantum spin systems

Host: Dr. Mark Novotony

Abstract:

      Many magnetic materials—some merely conventional but others quite exotic—can be well described as a collection of quantum spins, mutually coupled by antiferromagnetic interactions. Even in the absence of any specific material motivation, spin systems of this kind are widely used as toy models in which to study quantum criticality or to establish the existence of novel phases of matter. A recurring theme is that the low-energy sector of these models tends to have an effective description in terms of other, more geometric degrees of freedom, such as hard-core dimers or gases of closed strings or loops. I will highlight some of these correspondences in specific examples and illustrate how they can be exploited in theory and numerics.

April 1, 2015 Dr. Oscar A. Rondon, University of Virginia

SPIN PHYSICS PROGRAM IN JEFFERSON LAB’S HALL C

Host: Dr. Dipangkar Dutta

Abstract:

      The nucleon spin structure has been studied at Jefferson Lab's Hall C in experiments RSS (E01-006) and SANE (E07-003), which measured double spin asymmetries using the U. of Virginia solid polarized target and CEBAF's 6 GeV polarized electrons. The proton longitudinal spin structure g1 and transverse structure g2 have been investigated at kine-matics extending from the elastic point to DIS, for four-momenta squared ranging from 0.8 to 5 GeV squared. The neutron structures have been measured in the region of the nucleon resonances at 1.3 GeV squared on a deuteron target. Results of both experiments will be high-lighted. A brief survey of approved experiments for the 12 GeV pro-gram will also be presented.

Feb. 26, 2015 Dr. Jacquelyn J. Chini, University of Central Florida

One Size Fits All? Tailoring Course Transformation for Students and Instructors

Host: Dr. Chuji Wang

Abstract:

      In the Engage to Excel report, the President’s Council of Advisors on Science and Technology recommend widespread adoption of empirically validated teaching practices [1]. A recent meta-analysis found that active learning courses consistently outperform lecture courses across STEM disciplines, leading Carl Wieman to call continuing to teach with traditional lecture “the pedagogical equivalent of bloodletting” [2, 3]. Given this empirical and emotional support, why has the course transformation process been so slow? Others, however, raise a voice of skepticism about the “one size fits all” nature of such recommendations. Is every active learning course the same? If an instructional strategy has proven successful for a particular instructor and student population, will it be successful for every instructor and student population? I will present research on the many “players” involved in the transformation process—institutions, faculty, teaching assistants and students—and make the case that we need to carefully study differences across these populations to uncover the nuances of promising instructional strategies, allowing faculty to tailor strategies to their own context.

[1] Olson, S., & Riordan, D. G. (2012). Engage to Excel: Producing One Million Additional College Graduates with Degrees in Science, Technology, Engineering, and Mathematics. Report to the President. Executive Office of the President.
[2]. Freeman, S., Eddy, S. L., McDonough, M., Smith, M. K., Okoroafor, N., Jordt, H., & Wenderoth, M. P. (2014). Active learning increases student performance in science, engineering, and mathematics. Proceedings of the National Academy of Sciences.
[3] Wieman, C. E. (2014) Large-scale comparison of science teaching methods sends clear message. Proceedings of the National Academy of Sciences.

Feb. 11, 2015 Dr. Michael Strauss, University of Oklahoma

Measurements of the Properties of a Higgs Boson Using the ATLAS Detector at the LHC

Host: Dr. Gautam Rupak

Abstract:

      In July 2012 the ATLAS and CMS collaborations at the CERN Large Hadron collider announced the discovery of a Boson consistent with the predicted standard model Higgs Boson. Since that discovery, further measurements have given insight into the properties of this particle. This talk will discuss the importance of the Higgs Boson within the standard model, the discovery of this new Boson, and subsequent measurements of its properties. Searches for additional Higgs Bosons may also be discussed.

Feb. 6, 2015 Dr. Miles Stoudenmire, Perimeter Institute for Theoretical Physics

Exact Calculations in the One-Dimensional Continuum with DMRG

Host: Dr. Chuji Wang

Abstract:

      The density matrix renormalization group (DMRG) is a powerful method for solving one-dimensional quantum systems, but until recently has mainly been applied to lattice models. Applying DMRG to continuum 1D systems is difficult, but one is rewarded with results applicable to cold atom systems and electronic structure models; the latter providing insight into density functional theory (DFT) methods. I will describe how we overcome the challenges of studying continuum systems with long-range interactions, then focus especially on results for exact gaps and Kohn-Sham-DFT band gaps for weakly and strongly correlated electron systems.

Jan. 23, 2015 Dr. Robert L. Cooper, Indiana University

The Coherent Elastic Neutrino-Nucleus Scattering (CENNS) Experiment at Fermilab

Host: Dr. Gautam Rupak

Abstract:

      Low-energy neutrinos can have de Broglie wavelengths that are larger than target nuclei. At these energies, coherent elastic neutrino-nucleus scattering (CENNS) is predicted to be the dominant interaction, yet it remains unseen. Measuring CENNS is dicult because elastic scattering deposits very little energy in a detector and backgrounds are very difficult to control. Nevertheless, a discovery measurement is the first part in a larger program to use the CENNS interaction to understand supernova dynamics and detection, probe the weak interaction, and search for non-standard interactions and neutrino magnetic moments. The CENNS collaboration is planning to move the 500 kg, liquid argon detector MiniCLEAN to the Fermilab Booster Neutrino Beam for a first CENNS measurement. Without adequate shielding, MiniCLEAN will also be exposed to accelerator-correlated neutron backgrounds that can fake the CENNS signal. In this talk, I will describe the physics of CENNS, our plan for a first measurement at Fermilab, and our ongoing efforts to measure and mitigate neutron backgrounds. A exciting feature of our neutron measurement program is the novel, Indiana-built SciBath detector that recently measured neutron fluxes 20 m from the BNB accelerator target at Fermilab.

Jan. 20, 2015 Dr. Michael Chini, Townes Laser Institute

Probing and Controlling Ultrafast Electron Motion with Attosecond Transient Absorption Spectroscopy

Host: Dr. Chuji Wang

Abstract:

      Attosecond light pulses hold the promise for real-time measurement and control on the natural timescale of electron motion, allowing researchers to “film” the first steps of photo-induced chemical reactions and opening the door to “lightwave electronics” steered by sub-optical-cycle variations in an intense laser field. However, the experimental application of attosecond pulses to complex targets – beyond atoms and small molecules – has proven challenging, due to current limitations in both attosecond laser technology and time-resolved spectroscopic techniques. In this talk, I will discuss the application of attosecond pulses using a new technique – attosecond transi-ent absorption spectroscopy – to probe and control electron wavepackets in atomic and molecular targets. In addition, I will describe how new ultrafast laser architectures based on nonlinear optical techniques are currently push-ing the state-of-the-art in attosecond technology and promise to allow the first attosecond applications to chemical, biological, and condensed matter physics.

Jan. 16, 2015 Dr. George Shubeita, University of Texas at Austin

Molecular Motors: from Mechanics to Disease

Host: Dr. Chuji Wang

Abstract:

      Much like a city, living cells are organized, and main-taining their organization is essential for their proper functioning. To position micrometer-sized vesicles and organelles inside the cell at the right place and in a timely fashion the cell shuttles these cargoes along a network of intracellular roads (microtubules and actin filaments) using a set of molecular motor proteins (kinesin, dynein and myosin). These motor proteins use the energy released by ATP hydrolysis to generate the force they need to haul the cargoes; thus, measuring that force amounts to directly probing their function. Measuring the piconewoton forces that motors exert in their native cellular environment enabled us to count the number of motors hauling individual cargoes, and to test physical models of intracellular transport. Given the ubiquity of molecular motors, failure in regulating their function can result in disease. Neurodegenerative dis-eases such as Alzheimer’s, Huntington and Amyo-trophic Lateral Sclerosis, for example, have been linked to motor malfunction. Using a combination of genetic, biochemical and biophysical tools in a fruit fly model of Alzheimer’s disease, we established the mechanism by which the motor regulator GSK-3 alters transport when present in the elevated levels found in Alzheimer’s pa-tients. Our findings have implications on the develop-ment Alzheimer’s drugs targeting GSK-3.

Sep. 29, 2014 Dr. Russel White, Georgia State University

Newly Discovered Young Planets Constrain Formation and Migration Theories

Host: Dr. Angelle Tanner

Abstract:

      Our understanding of planet formation and migration is limited by both the poorly constrined ages of young stars and the death of known planets orbiting them. I'll present results from two observation programs that directly address these. The first uses Georgia State's CHARA Array to measure the angular sizes of young stars, permitting more robust age estimates. The ssecond is a multi-wavelength radial velocity search by young and adolescent aga planets. Our discoveries include the first hot- and warm-Jupiters in the nearest open clusters.

Sep. 10, 2014 Dr. Greg Smith, Jefferson Laboratory

Early Results From The Qweak Experiment

Host: Dr. Dipangkar Dutta

Abstract:

      A subset of results from the recently completed Jefferson Lab Qweak experiment will be reported. This experiment, sensitive to physics beyond the Standard Model, exploits the small parity violating asymmetry in elastic p scattering to make the first direct measurement of the proton’s weak charge. The experiment employed a 180 μA longitudinally polarized 1.16 GeV/c electron beam on a 35 cm long liquid hydrogen target. Scattered electrons in the angular range θ < 12° corresponding to were detected in one of eight Cerenkov detectors arrayed symmetrically about the beam axis.
     The goals of the experiment were to provide a measure of $QP$_W to 4.1%, which implies a measure of $sin2($θ_W) to 0.3%, and to provide a tight constraint on a combination of the vector weak quark charges $C$_1u and $C$_1d . Aspects of the experimental method will be described, with a focus on the challenges presented and met by the world’s highest power $LH$₂ target. The new constraints on $C$_1u and $C$_1d provided by the subset of the experiment’s data analyzed to date will also be shown.

Aug. 21, 2014 Dr. Krishna Adhikari, Mississippi State University

Measurement of deuteron’s spin structure function g1 and its moments at low momentum transfers ($Q2$)

Host: Dr. Lamiaa El Fassi

Abstract:

      Double polarization cross section differences (Δσ$$_||) for proton and deuteron targets have been measured in the EG4 experiment using the CLAS detector at Jefferson Lab by scattering longitudinally polarized electron beams at relatively low energies (1.0 - 3.0 GeV) from the CEBAF accelerator off longitudinally polarized $NH$₃ and $ND$₃ targets. Looking at very low scattering angles (down to 6°) with the help of a new dedicated Cherenkov counter and a special magnetic field setting of the CLAS detector, data were collected in the resonance region () at very low momentum transfers ($Q2$ on deuteron was as low as $0.02\; GeV2$). I will discuss the importance, measurement and analysis of the deuteron part of the EG4 data from which spin structure function $g$₁ is extracted and some of its moments are evaluated. These measurements extend and improve the world deuteron data on $g$₁ to the previously unmeasured low $Q2$ region. In combination with the corresponding proton data from the same experiment, this data will be valuable to extract $g$₁ of neutron in the same kinematics which, in turn, will help shed more light on the nucleon spin structure in the region of quark-confinement as well as in the transition region between hadronic and partonic degrees of freedom. In addition, evaluated moments of g1 are compared with predictions from different Chiral Perturbation Theory (χPT) calculations and phenomenological models which attempt to explain the nucleon internal structure and dynamics in the measured region.

2014-2015 Committee