2016-2017 Colloquia Abstracts

Return to the 2016-2017 Colloquia Schedule

Thursday, Sept. 22, 2016

Some photons, an electron, and an atom

Bruno deHarak, Illinois Wesleyan University
Experiment apparatus

Laser-assisted electron-atom scattering (LAES) experi-ments try to answer a simple question: what happens when an electron scatters from a target in the presence of a laser field? Laser-assisted free-free (LAFF) processes are the simplest, and were the first experimentally examined, examples of LAES experiments. In LAFF experiments, the presence of a laser field reduces the amplitude of the elastic peak, and produces a series of sidebands. The side-bands below the elastic peak are the result of photon emission by the scattered electron, while the higher ener-gy sidebands result from photon absorption. This talk will provide an overview of various types of LAES experi-ments, with focus on our recent LAFF experiments and simulations.


Return to the 2016-2017 Colloquia Schedule


Thursday, Oct. 6, 2016

The success of New Horizons: NASA’s first mission to Pluto

Nathaniel Cunningham, Nebraska Wesleyan University
Diagram of detection of Pluto's atmosphere as Pluto occults the Sun

NASA’s New Horizons spacecraft executed a fly-by of the Pluto system in July 2015, carrying out the first-ever (and last for a long time!) close-up exploration of this distant, icy world. This talk will introduce the Pluto system, the motivation for a mission to Pluto and the Kuiper Belt, and the New Horizons mission and instrument suite. I will present some of the startling facts that New Horizons has revealed about this richly-varied planet in the last year: active geology, an atmosphere more compact than expected, chaotically-tumbling moons. Finally, I will discuss what the future holds for New Horizons as it continues to traverse the outer solar system, and carries out an encore performance in 2019 with close investigation of a Kuiper Belt object.

Bio: Nathaniel is a Lincoln native, and earned his PhD in Astrophysics at the University of Colorado. In his research, he has developed astronomical instruments and used them to study the births and deaths of stars; developed detector systems for the Diocles high-power laser system at UNL; and he currently uses the Hubble Space Telescope to carry out spectoscopic studies of the surfaces and atmospheres of small bodies and moons in the Solar System. Since 2007, he has contributed to calibration of instruments on NASA's New Horizons mission to Pluto, and on the European Space Agency's recently-concluded "Rosetta" mission orbiting a comet. He joined the Physics & Astronomy facul-ty at Nebraska Wesleyan University in 2010.


Return to the 2016-2017 Colloquia Schedule


Thursday, Oct. 27, 2016

X-ray snapshots of molecules in motion

Anne Marie March, Argonne National Laboratory
Diagram of x-ray and laser pulses flowing into jet of molecules

X-ray spectroscopy is a powerful means of obtaining structural information about molecules, which includes the positions of atoms as well as energies and populations of electronic orbitals. Because each element of the periodic table has characteristic absorption and emission lines, by tuning X-ray energy one can selectively probe the local structure surrounding a particular atom within a molecule. Because of the penetration power of hard X-rays, one can probe molecules that are embedded in bulk environments, such as solutions. In this talk I will discuss hard X-ray spectroscopy techniques that allow us to see structural changes that occur as molecules react. The measurements make use of the ultrashort picosecond (10-12 s) duration pulses available at synchrotron sources as well as the femtosecond (10-15 s) duration pulses that are becoming avail-able at new X-ray free electron lasers.

Bio: Anne Marie March received a B. A. in Physics from the College of the Holy Cross and a Ph.D. in Physics from Stony Brook University. She joined the Atomic, Molecular, and Optical Physics group at Argonne National Laboratory as a postdoctoral researcher and is now an Assistant Physicist in the group. Her current research interests include fundamental light-matter interactions, the dynamics of photoexcited molecules in solutions, ultrafast X-ray techniques, and laser control of chemical reactions.


Return to the 2016-2017 Colloquia Schedule


Thursday, Nov. 3, 2016

Fabrication and Characterization of Magnetic Heteronanostructures – Knowing the world at the nanoscale

Ruihua Cheng, Indiana University-Purdue University Indianapolis

The fact that graphene's 2D electron system is unprotected from the environment is often detrimental: while the electron mobility is high compared to most semiconductors, it is generally far lower than it could be due to scattering from extrinsic disorder. However, perhaps the interactions between graphene's quasi-relativistic electrons and the various surface contaminants can be turned to advantage. For instance, can the electronic structure of graphene be controllably altered? We are starting to explore the possibility of adatom-induced spin-orbit couplings in graphene in order to realize the original topological insulator predicted by Kane and Mele in 2005. Initial experiments on dilute coatings of indium atoms on graphene will be presented, as well as our current efforts with osmium.

Bio: Ruihua Cheng is currently working at the Department of Physics of Indiana University-Purdue University Indianapolis as an Associate Professor. From 2005-2013, she was an Assistant Professor at IUPUI, and she was promoted to Associate Professor in 2013. During 2002-2005, she performed her postdoc research in magnetic thin film group of Argonne National Laboratory, and before that she received her Ph.D. in Physics at University of Nebraska–Lincoln, under the direction of Dr. Peter Dowben. Her research is focused on the study of nanomagnetism through the fabrication and characterization of magnetic nanostructure materials with the goal of understanding the new materials’ phenomena and exploring and potential technological applications.


Return to the 2016-2017 Colloquia Schedule


Thursday, Nov. 10, 2016

From laser plasma wakefield acceleration to table top radiation source

Min Chen, Key Laboratory for Laser Plasams (MOE), Department of Physics and Astronomy, Shanghai Jiao Tong University, China
A LWFA and plasma based compact radiation source

Laser wakefield acceleration (LWFA) has three orders of magnitude larger accelerating gradient than traditional ones and it is very promising to be the candidate accelerator for the next generation of compact radiation sources. In this talk I will give a short review on the LWFA and focus on the high quality electron beam generation and a new type of plasma based undulator.

To get low energy spread electron beam, two injection schemes are proposed here. By use of certain initially unmatched laser pulses, the electron injection can be constrained to the very front region of the mixed gas target, typically in a length of a few hundreds micro meters determined by laser-driven bubble deformation, and energy spread is largely reduced [1,2]. By using this method, electron beam with FWHM energy spread less than 5% and peak energy around 500MeV is demonstrated by simulations. In a second scheme, we suggest to use two-color beat wave to control the injection length [3]. Due to the phase velocity difference of the two color pulses, the ionization distance is very limited which then lowers the injection length. We demonstrate electron beam with ultralow energy spread less than 1% percent and central energy of 400MeV can be obtained by using ω and 3ω laser pulses in a gas.

To make a compact radiation source, we propose an all-optical synchrotron-like radiation source based on laser-plasma acceleration and plasma undulator (see Fig. 1). With the laser pulse off-axially injected in a straight channel, the centroid oscillation of the pulse causes a wiggler motion of the whole accelerating structure including the trapped electrons, leading to strong synchrotron-like radiations with tunable spectra [4,5]. It is further shown that a ring-shaped synchrotron is possible in a curved plasma channel. Due to the intense acceleration and bending fields inside plasmas, the central part of the sources can be made within palm size. With its potential of high flexibility and tunability, such compact light sources once realized would find applications in wide areas and make up the shortage of large synchrotron radiation facilities.

References:

  1. M. Zeng, M. Chen, Z.M. Sheng et al., Phys. Plasmas, 21, 030701 (2014).
  2. M. Mirzaie, et al., Sci. Rep. 5, 14659 (2015).
  3. M. Zeng, M. Chen, L.L. Yu et al., Phys. Rev. Lett. 114, 084801 (2015).
  4. M. Chen, J. Luo, F.Y. Li, et al, Light:Science & Applications, 5, e16015 (2016).
  5. J. Luo, M. Chen, et al., “A compact tunable polarized X-ray source based on laser-plasma helical undulaotors”, Sci. Rep. 6, 29101 (2016).

Bio: Min Chen received his PhD degree from Institute of Physics, Beijing, Chinese Academy of Sciences (CAS) in 2007. From 2007 to 2009 he worked as an Alexander von Humboldt postdoctoral research fellow in Heinrich Heine Universitaet, Duesseldorf, Germany. After that he joined LOASIS program at Lawrence Berkeley National Laboratory (LBNL) as a postdoctoral research fellow. From 2012, he joined Shanghai Jiao Tong University as a Distinguished Research Fellow.

His main research interests are laser plasma based particle accelerator and radiation sources including laser wakefield accelerator, laser solid ion acceleration and radiation sources from laser plasma interaction. Since 2006 he coauthored more than 100 peer-reviewed scientific research papers including 8 published in Physical Review Letters and 1 in PNAS, among them 30 are first author or corresponding author. The total citation number of these publications is more than 1500, H index is 21.


Return to the 2016-2017 Colloquia Schedule


Thursday, Nov. 17, 2016

Physics after the lab and the desk: Your work in Physical Review Letters

Dr. Samindranath Mitra, Editor, Physical Review Letters
Samindranath Mitra

Physics research takes place mostly at your desk, at the keyboard, in the lab. You communicate results through posters, talks, and papers—leading to, hopefully, wide dissemination and recognition. The sequence entails interacting with journal editors, referees, conference chairs, journalists, and so on. I will focus on this post-research collaborative process in physics, primarily through the lens that is Physical Review Letters.

Bio: Samindranath (Sami) grew up in Kolkata and Delhi, and received his Ph.D. at Indiana University (Bloomington) in 1994 on theoretical aspects of the quantum Hall effect. After working on chemical physics at the Albert Einstein College of Medicine in New York City, he joined Physical Review Letters. Among his other responsibilities are papers on transport properties in semiconductors, 2D materials, and mesoscopic systems.


Return to the 2016-2017 Colloquia Schedule


Thursday, Dec. 1, 2016

Electron Collisions – Experiment, Theory, and Applications

Klaus Bartschat, Drake University
Diagram of electron collision data

Electron collisions with atoms, ions, and molecules represent one of the very early topics of quantum mechanics. In spite of the field's maturity, a number of recent developments in detector technology (e.g., the "reaction microscope" or the "magnetic-angle changer") and the rapid increase in computational resources have resulted in significant progress in the measurement, understanding, and theoretical/computational description of few-body Coulomb problems. Close collaborations between experimentalists and theorists worldwide continue to produce high-quality benchmark data, which allow for thoroughly testing and further developing a variety of theoretical approaches. As a result, it has now become possible to reliably calculate the vast amount of atomic data needed for detailed modeling of the physics and chemistry of planetary atmospheres, the interpretation of astrophysical data, optimizing the energy transport in reactive plasmas, and many other topics—including light-driven processes, in which electrons are produced by continuous or short-pulse ultra-intense electromagnetic radiation.

In this talk, I will highlight some of the recent developments that have had a major impact on the field. This will be followed by showcasing examples, in which accurate electron collision data enabled applications in fields beyond traditional AMO physics. Finally, open problems and challenges for the future will be outlined.

*This work is supported by the National Science Foundation under grants No. PHY-1403245 and PHY-1520970, and by the XSEDE supercomputer allocation PHY-090031.


Return to the 2016-2017 Colloquia Schedule


Wednesday, Jan. 11, 2017

Saturn's Rings and Icy Moons from Cassini

Philip Nicholson, Cornell University
Saturn with full view of rings

Bio: Professor Nicholson has been on the faculty of the Department of As-tronomy at Cornell University since 1982. An Australian by birth, he com-pleted a Ph.D. in Planetary Science at the California Institute of Technolo-gy in 1978 as a Fulbright Scholar. Before moving to Cornell, he held post-doctoral positions at Mount Stromlo Observatory in Australia and at the Jet Propulsion Laboratory in California. His research centers on two main areas: the orbital dynamics of planetary ring systems and natural satel-lites, and infrared observational studies of planets, their satellites and rings. His work has included studies of the ring systems of Saturn, Uranus and Neptune via Voyager observations and ground-based stellar occulta-tions; Earth-based observations with the 5-meter Hale telescope at Palo-mar of the small moons of Jupiter and Saturn discovered by the Voyager spacecraft; dynamical investigations of the planetary system around the pulsar PSR 1257 + 12, and of the rotational evolution of natural satellites. In 1997, he was a co-discoverer of the first irregular moons of Uranus, Cal-iban and Sycorax.

Prof. Nicholson is a member of the Visual Infrared Mapping Spectrometer science team on the NASA/ESA Cassini mission to Saturn, and was the leader of a team of Cornell and Caltech astronomers studying the impact of comet Shoemaker-Levy 9 into Jupiter in July 1994 using the Hale tele-scope.


Return to the 2016-2017 Colloquia Schedule


Thursday, Jan. 26, 2017

Achieving Atomic-level Design of Structures and Properties of Materials by Tailoring Interfaces in Solids

Jian Wang, University of Nebraska–Lincoln
Multi-Scale Interfaces Design in Solids modeling

Interfaces are common planar defects in solids. Interface can act as barriers, sinks and sources for other defects. By tailoring interface structures and properties, materials can be designed to achieve unusual properties, such as high strength, good ductility, high toughness, and high irradiation tolerance. This can be accomplished through two steps: (1) Discover unusual mechanical behavior (e.g., high strength and good ductility) of nanostructured composites, and Develop theory and fundamental understanding of unusual mechanical behavior. (2) Transform fundamental understanding of structural characters and deformation physics of nanostructured composites into a mesoscale capability of discovering, predicting, and designing superior nanostructured materials (strength, ductility, toughness, and radiation). To achieve this goal, multi-scale methods including experiment and theory and modeling are necessary. In this talk, I will present fundamental principles in developing interface-dominated composites, and the development of experimental techniques and materials modeling tools at different scales.

Bio: Dr. Jian Wang is an Associate Professor at Mechanical and Materials Engineering at University of Nebraska-Lincoln. He received his Ph.D in Mechanical Engineering, Rensselaer Polytechnic Institute, Troy, NY, USA, in 2006. After that, He has been working as Technical Staff Member for 9 years at Los Alamos National Laboratory. Currently, his research interests are focused on more quantitative exploring the structure-properties relationships of structural and nanostructured materials. He was awarded International Journal of Plasticity Young Research Award, 2015; TMS MPMD Young Leader Professional Development Award, 2013; the LDRD/Early Career Award (2011); and the LANL Distinguished Postdoctoral Performance Award in 2009. He has ~200 peer-reviewed publications (~5500 citations and H-index = 44), two book chapters in Dislocations in Solids and 70+ invited/keynote presentations. He is serving as Editorial Boards for several materials journals.


Return to the 2016-2017 Colloquia Schedule


Thursday, Feb. 9, 2017

2D Materials: From Macroscopic Perfection to Emerging Nanoscale Functionality

Peter Sutter, University of Nebraska–Lincoln
Photos of nanomaterial in increasing scale from 10 μm to 2nm

Two-dimensional (2D) materials, such as graphene, hexagonal boron nitride and a family of metal chalcogenides represent a class of atomically thin crystals that have fascinating fundamental properties and show promise for a wide range of applications. Larger homogeneous areas of these materials have been investigated intensely. Much less understood are effects that arise in heterogeneous materials, either near naturally occurring defects, impurities, and boundaries, or as a result of intentional alloying and interface formation. Addressing such systems experimentally involves significant challenges: Understanding atomistic growth mechanisms, so that systems with specific “imperfections” and controlled interfaces can be realized; and probing emerging local properties at scales that match the relevant length scales in heterogeneous systems. I will discuss our recent progress in addressing these challenges by in-situ microscopy of the growth and processing of 2D materials and heterostructures, and by spatially resolved measurements of electronic structure and optoelectronic properties. The results contribute to a foundation for robust technologies that harness inherent or engineered heterogeneity in atomically thin materials.

Bio: Peter Sutter received his Diploma and Doctorate in Physics from ETH Zurich, Switzerland. Following a Swiss National Science Foundation Postdoctoral Fellowship at the University of Wisconsin-Madison, he was Assistant/Associate Professor at the Colorado School of Mines and Group Leader at Brookhaven National Laboratory before joining the University of Nebraska-Lincoln in 2015 as a Professor in Electrical and Computer Engineering. His research focuses on the growth and electronic properties of two-dimensional materials and nanomaterials for energy conversion processes, studied primarily by novel in-situ microscopy and measurement techniques. He received several awards, among which the NSF Career Award, the Scientific American 50 Award, and the Sapphire Prize. He has authored more than 160 peer-reviewed publications, presented numerous invited talks, and holds 7 U.S. Patents.


Return to the 2016-2017 Colloquia Schedule