SYMPOSIUM ON ULTRAFAST DYNAMICS OF ATOMS

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EVENT PROGRAM
sponsored and organized by NEBRASKA EPSCor
in support of nebraska/kansas nsf collaborative project
funded by the National Science Foundation
Research Infrastructure Improvement Program Track-2 grant #1430519
2015 Nebraska Research & Innovation Conference
SYMPOSIUM ON ULTRAFAST
DYNAMICS OF ATOMS, MOLECULES
& NANOSTRUCTURES
unl office of research and economic development
SEPTEMBER 29 | LINCOLN, NEBRASKA
epscor.nebraska.edu
Message from the Nebraska EPSCoR Director
Dear Participants,
Notes:
It is my pleasure to welcome you to the Symposium on Ultrafast Dynamics of Atoms, Molecules
& Nanostructures, and I thank our speakers for sharing their time and expertise with us.
Today’s event is a continuation of an annual series of conferences and symposia that Nebraska
EPSCoR has been organizing in support of Nebraska researchers. This event is special because
it is organized in support of collaborative research efforts of Nebraska and Kansas in AMO
physics, funded by a three-year NSF EPSCoR grant.
Please enjoy today’s knowledge transfer and networking opportunities, and make sure to visit
the poster session to learn about exciting AMO research being conducted in Nebraska and
Kansas.
Thank you for joining us!
Best,
F. Fred Choobineh, P.E., Ph.D.
Director, Nebraska EPSCoR
Blackman Distinguished Professor of Electrical Engineering, UNL
Table of Contents
Agenda . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
Morning Session . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
Afternoon Session . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
Poster Session Abstracts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
Symposium Organizing Committee:
Nebraska EPSCoR Staff:
Anthony Starace, University of Nebraska-Lincoln (committee chair)
Herman Batelaan, University of Nebraska-Lincoln
Itzik Ben-Itzhak, Kansas State University
Kristin Bowman-James, Kansas EPSCoR
Doug Byers, Kansas EPSCoR
Martin Centurion, University of Nebraska-Lincoln
Rosemary Blum, Kansas EPSCoR
Fred Choobineh, Nebraska EPSCoR
Uwe Thumm, Kansas State University
Vinod Kumarappan, Kansas State University
Frederick N. Gartner, Accounting Technician
Nancy Simnitt, Executive Assistant
Carole Wilbeck, Communications Specialist
_____________________________________________________
Clint Chapman, Symposium Website Designer
2015 NEBRASKA RESEARCH & INNOVATION CONFERENCE
2015 NEBRASKA RESEARCH & INNOVATION CONFERENCE
SYMPOSIUM on ultrafast dynamics of atoms, molecules & nanostructures
TUESDAY, SEPTEMBER 29 | LINCOLN, NEBRASKA
7:30 am
Registration and Continental Breakfast
8:30 am
Opening Remarks
Dr. Prem Paul, University of Nebraska-Lincoln
8:45 am
Metasurfaces: New Frontiers in Structured Light and Surface Waves
Dr. Federico Capasso, Harvard University
9:30 am
Condensed Matter in Ultrafast and Superstrong Fields: Attosecond Phenomena
Dr. Mark I. Stockman, Georgia State University
10:15 a.m. Break
10:45 am QASER: From Radio Frequencies to Optical Domain
Dr. Anatoly Svidzinsky, Texas A&M University
11:30 am Ultrafast Electron Motion in Atoms and Molecules
Dr. Philip H. Bucksbaum, Stanford University
12:15 p.m. Lunch
1:30pm
Attosecond Dynamics: From Atoms to Semiconductor Solids
Dr. Stephen Leone, University of California, Berkeley
2:15 pm
Understanding and Modeling Ultrafast Molecular Dynamics from First Principles
Dr. Todd Martinez, Stanford University
3:00 p.m. Break
session chair
dr. anthony starace
university of nebraska-lincoln
session chair
dr. herman batelaan
university of nebraska-lincoln
session chair
dr. matthias fuchs
university of nebraska-lincoln
3:30 pm
Angle-Resolved Measurements Using Rotational Wavepackets in Asymmetric Top Molecules
Dr. Vinod Kumarappan, Kansas State University
session chair
3:55 pm
Ultrafast Electron Transport In and Between Single Atomic Layers
dr. uwe thumm
Dr. Hui Zhao, University of Kansas
kansas state university
4:20 pm Diffractive Imaging of Isolated Molecules with Femtosecond Electron Pulses
Dr. Martin Centurion, University of Nebraska-Lincoln
4:45 p.m. Poster session and reception (ends at 6:30 p.m.)
2015 NEBRASKA RESEARCH & INNOVATION CONFERENCE
1
SYMPOSIUM on ultrafast dynamics of atoms, molecules & nanostructures
Metasurfaces: New Frontiers in Structured
Light and Surface Waves
Condensed Matter in Ultrafast and
Superstrong Fields: Attosecond Phenomena
FEDERICO CAPASSO
Robert Wallace Professor of Applied Physics
and Vinton Hayes Senior Research Fellow in Electrical Engineering
School of Engineering and Applied Sciences, Harvard University
mark i. stockman
Professor of Physics and Director of the Center for Nanooptics (CeNO)
Georgia State University
8:45– 9:30 A.M.
ABSTRACT: Patterning surfaces with subwavelength spaced metallodielectric features (metasurfaces) allows local control of the amplitude,
phase and polarization of scattered light, and generation of complex
wavefronts such as optical vortices of different topological charge and
dislocated wavefronts. Recent results on achromatic metasurfaces will
be presented including lenses and collimators. Metasurfaces have also
become a powerful tool to shape surface plasmon polaritons (SPPs)
and, more generally, surface waves. I will present new experiments on
imaging SPPs that have revealed the formation of Cherenkov SPP wakes
and demonstrated polarization sensitive light couplers that control the
directionality of SPPs and lenses which demultiplex focused SPP beams
depending on their wavelength and polarization.
BIO: Dr. Federico Capasso is the Robert Wallace Professor of Applied
Physics at Harvard University, which he joined in 2003 after 27 years at
Bell Labs where he was Member of Technical Staff, Department Head
and Vice President for Physical Research. He pioneered band-structure
engineering of semiconductor nanostructures and quantum devices,
including the invention and realization of the quantum cascade laser,
and reported the first measurement of the repulsive Casimir force. In the
past decade he has focused on wavefront control using plasmonics and
on a new approach to diffractive optics based on metasurfaces, known
as flat optics. Key results of this research include the formulation and
demonstration of the generalized laws of refraction and reflection and
aberration free flat lenses. He is a member of the National Academy
of Sciences and the National Academy of Engineering, a fellow of the
American Academy of Arts and Sciences, and a foreign member of the
Accademia dei Lincei. His awards include the IEEE Sarnoff Award, the
Materials Research Society Medal, the Franklin Institute Wetherill Medal,
the Rank Prize in Optoelectronics, the Optical Society Wood Prize, the
IEEE Edison Medal, the American Physical Society Arthur Schawlow Prize
in Laser Science, the King Faisal Prize, the Berthold Leibinger Zukunft
Prize, the Julius Springer Prize in Applied Physics, the Institute of Physics
Duddell Medal, the Jan Czochralski Award for lifetime achievements in
Materials Science, the European Physical Society Quantum Electronics
Prize, the SPIE Gold Medal and the Gold Medal of the President of Italy
for meritorious achievement in science. He holds honorary doctorates
from Lund University, Diderot University and the Universities of Bologna
and Roma II (Tor Vergata).
2
9:30 - 10:15 A.M.
ABSTRACT: We discuss a new class of phenomena in condensed
matter optics when a strong optical field ~1-3 V/Å reversibly changes a
solid within an optical cycle. Such a pulse drives ampere-scale currents
in dielectrics and controls their properties, including optical absorption
and reflection, extreme UV absorption, and generation of high harmonics
in a non-perturbative manner on a 100-as temporal scale. Applied to a
metal, such a pulse causes an instantaneous and reversible loss of the
metallic properties. We will also discuss our latest theoretical results on
graphene that in a strong ultrashort pulse exhibits unique behavior. New
phenomena are predicted for buckled two-dimensional solids, silicene
and germanine. These are fastest phenomena in optics unfolding within
a half period of light. They offer the potential for petahertz-bandwidth
signal processing, generation of high harmonics on a nanometer spatial
scale, etc.
BIO: Mark I. Stockman received his PhD and DSc degrees from
institutes of the Russian Academy of Sciences. He is a Professor of
Physics and the Director of the Center for Nanooptics (CeNO) at
Georgia State University, Atlanta, GA, USA. He is a Fellow of the
American Physical Society, Optical Society of America, and SPIE – The
International Society for Optoelectronic Engineering. He has served as a
Distinguished Visiting Professor at Ecole Normale Supérieure de Cachan
(France) and as a Visiting Professor at Ecole Supérieure de Physique and
de Chimie Industrielle (Paris, France), and also as a Guest Professor
at University of Stuttgart (Germany), Max Plank Institute for Quantum
Optics (Garching, Germany), and Ludwig Maximilian University
(Munich, Germany). A major direction of his research is theoretical
nanoplasmonics and strong-field ultrafast optics. He is a co-inventor
of the spaser (nanoplasmonic laser). He is an author of over 190 major
research papers and has presented numerous plenary, keynote, and
invited talks at major international conferences. He gave lectures and
taught courses on nanoplasmonics and ultrafast optics at many major
international meetings and scientific institutions in the US, Canada,
Europe, Asia, and Australia.
2015 NEBRASKA RESEARCH & INNOVATION CONFERENCE
SYMPOSIUM on ultrafast dynamics of atoms, molecules & nanostructures
QASER:
From Radio Frequencies to Optical Domain
Ultrafast Electron Motion in Atoms and
Molecules
ANATOLY SVIDZINSKY
Research Associate Professor, Department of Physics & Astronomy
Texas A&M University
PHILIP H. BUCKSBAUM
Marguerite Blake Wilbur Professor in Natural Science
Stanford University
10:45 – 11:30 A.M.
11:30 A.M. – 12:15 P.M.
ABSTRACT: Collective interaction of light with atomic ensembles
occurring on fast superradiant time scales can yield light amplification
at high frequencies by the process of difference combination resonance.
A device that generates high frequency coherent radiation by driving an
atomic ensemble with a much smaller frequency is called the QASER.
Amplification mechanism of the QASER is governed by the difference
combination parametric resonance which occurs when the driving
field frequency matches the frequency difference between two normal
modes of the coupled light atom system. I will review the concept of
the QASER making a connection with the combination resonance in a
system of asymmetrically coupled parametric oscillators and inverted
pendulum. I will demonstrate the QASER amplification mechanism at
radio frequencies in coupled RLC circuits and microwave cavities. I will
also discuss possible realization of the QASER at optical frequencies in
gases and nonlinear media with negative refractive index or materials
with strong anomalous dispersion.
ABSTRACT: The timescale for internal motion in atoms and small
molecules is determined by their Angstrom sizes and Rydberg binding
energies to be femtoseconds or shorter. The binding fields for the
outermost electrons are tens of volts per Angstrom, while inner electrons
can be bound by kilovolts or more. I will describe recent experiments
designed to study the internal motion of electrons and nuclei in
molecules utilizing laser fields on these scales of time, photon energy
and field strength. Two kinds of laser sources are employed: strong
focused infrared lasers, and X-ray free electron lasers.
BIO: Anatoly Svidzinsky is a research associate professor with the
Department of Physics & Astronomy at Texas A&M University. He
received two Ph.D. degrees, from Moscow Institute of Physics and
Technology in 1997 and Stanford University in 2001. His research
interests in theoretical physics include quantum optics, Bose-Einstein
condensation, superconductivity, chemical physics and astrophysics. He
is best known for his work on collective, nonlocal and virtual effects in
emission of atomic ensembles; development of novel coherent sources
of radiation; pioneering work on dynamics of superfluid vortices;
Bose-Einstein condensate statistics; prediction of novel magnetic,
thermal and transport properties of high temperature superconductors;
development of description of the chemical bond based on dimensional
scaling analysis; prediction of a new mechanism of neutron star radiation
produced by superfluid core and invention of an alternative vector theory
of gravity. He is an author of about 100 research papers.
BIO: Philip H. Bucksbaum is the Marguerite Blake Wilbur Professor in
Natural Science at Stanford University, in the Physics, Applied Physics,
and Photon Science departments. He directs the PULSE Institute at
Stanford and SLAC. Bucksbaum graduated from Harvard College (A.B.
1975) and the University of California at Berkeley (M.A. 1978; Ph.D.
1980). He was previously on the University of Michigan faculty and the
Technical Staff at Bell Laboratories. He has been elected to the National
Academy of Sciences and the American Academy of Arts and Sciences,
and is a Fellow of the American Physical Society and the Optical Society.
2015 NEBRASKA RESEARCH & INNOVATION CONFERENCE
3
SYMPOSIUM on ultrafast dynamics of atoms, molecules & nanostructures
LUNCH 12:15 - 1:30 p.m.
Please enjoy lunch with colleagues
in the Regents Ballroom C.
We look forward to your participation at
the poster session in Regents Ballroom C
following today’s sessions!
Attosecond Dynamics: From Atoms to
Semiconductor Solids
stephen leone
John R. Thomas Endowed Chair in Physical Chemistry,
Professor of Chemistry and Physics
University of California, Berkeley
1:30 - 2:15 P.M.
ABSTRACT: Intriguing physics and chemistry problems abound in
the pursuit of attosecond science, as such measurements push the
boundaries of fundamental electron dynamics timescales. The x-ray
transitions accessed by attosecond pulses are responsive to charge,
chemical oxidation state, and electronic environment, and they exhibit
sensitive shifts even with vibrational excitation. An introduction to
attosecond measurements is presented, with a basic goal to reveal
new dynamical timescales. Investigations involve the development of
methods to explore coherent electronic superpositions and timescales
for autoionization, strong-field ionization, and in the solid-state
to determine how fast a band gap or strongly correlated material
responds upon carrier excitation.
BIO: Stephen Leone is the John R. Thomas Endowed Chair in
Physical Chemistry, Professor of Chemistry and Physics at the
University of California, Berkeley, and faculty investigator, Lawrence
Berkeley National Laboratory. His research interests are ultrafast and
attosecond laser investigations of atomic, molecular, and solid state
dynamics. His honors include the American Chemical Society Award in
Pure Chemistry, the Herbert P. Broida Prize of the American Physical
Society, the Bourke Medal of the Faraday Division of the Royal Society
of Chemistry, the American Chemical Society Peter Debye Award,
the Polanyi Medal of the Gas Kinetics Division of the Royal Society of
Chemistry, and the Irving Langmuir Prize in Chemical Physics of the
American Physical Society. He is a member of National Academy of
Sciences and Fellow of the American Academy of Arts and Sciences.
4
2015 NEBRASKA RESEARCH & INNOVATION CONFERENCE
SYMPOSIUM on ultrafast dynamics of atoms, molecules & nanostructures
Understanding and Modeling Ultrafast
Molecular Dynamics from First Principles
TODD MARTINEZ
Ehrsam and Franklin Professor of Chemistry
Stanford University
2:15 – 3:00 P.M.
ABSTRACT: The Born-Oppenheimer approximation (BOA), arising
from the mass disparity between electrons and nuclei, is a cornerstone of
theoretical chemistry. Within this approximation, the electronic state of
a molecule is well-defined and independent of nuclear motion. However,
the BOA must break down when multiple electronic states are involved,
and this must be the case when a molecule is promoted to an excited
electronic state (for example by light absorption). In order to describe
such phenomena, we must introduce quantum mechanical descriptions
for both the electrons and nuclei. In this talk, I will give an overview of
our current understanding of ultrafast molecular dynamics beginning on
excited electronic states and the breakdown of the BOA. By solving both
the electronic and nuclear Schroedinger equations simultaneously, we
can calculate this dynamics for molecular systems ranging from smaller
paradigmatic cases to larger practically relevant ones. We illustrate these
ideas with photoinduced cis-trans isomerization and excited state proton
transfer (using molecules in isolation, solution and protein environments
as examples).
BIO: Todd Martínez received his B.S. in Chemistry from Calvin College
in 1989 and his Ph.D. in Chemistry from the University of California
at Los Angeles in 1994. From 1994 to 1996, he was a Fulbright Junior
Postdoctoral Researcher at Hebrew University in Jerusalem and a
University of California President’s Postdoctoral Fellow at UCLA. In 1996,
he joined the faculty in the Department of Chemistry at the University
of Illinois. He rose through the ranks to become the Gutgsell Chair in
Chemistry. In 2009, he was recruited to join the faculty at Stanford
University and the SLAC National Accelerator Laboratory, where he is
currently David Mulvane Ehrsam and Edward Curtis Franklin Professor.
Angle-Resolved Measurements Using
Rotational Wavepackets in Asymmetric Top
Molecules
vinod kumarappan
Associate Professor of Physics
Kansas State University
3:30 – 3:55 P.M.
ABSTRACT: Conventional methods of making molecular frame
measurements do not work well for asymmetric top molecules due to the
difficulties in aligning the molecules and in determining their orientation
by momentum imaging of fragments. Rotational wavepacket dynamics
offers a new route to molecular frame measurements in such molecules,
enabling simultaneous characterization of the orientation dependence
of ultrafast processes and the rotational wavepacket itself. This variation
of rotational coherence spectroscopy will be discussed using strong field
ionization and fragmentation of ethylene as examples.
BIO: Vinod Kumarappan received his Ph.D. from Tata Institute of
Fundamental Research, Mumbai, for research on laser-generated
plasmas in rare-gas clusters. After postdoctoral work first at University of
Maryland at College Park and then at Aarhus University, he joined Kansas
State University in 2007 as an assistant professor in the department of
physics. His current research interests include measurements in the
molecular frame, photoelectron spectroscopy and ultrafast electron
diffraction.
2015 NEBRASKA RESEARCH & INNOVATION CONFERENCE
5
SYMPOSIUM on ultrafast dynamics of atoms, molecules & nanostructures
Ultrafast Electron Transport In and Between
Single Atomic Layers
Diffractive Imaging of Isolated Molecules
with Femtosecond Electron Pulses
HUI ZHAO
Associate Professor of Physics
University of Kansas
MARTIN CENTURION
Associate Professor, Department of Physics and Astronomy
University of Nebraska-Lincoln
3:55 - 4:20 P.M.
4:20 – 4:45 P.M.
ABSTRACT: This presentation will convey the Nebraska-Kansas
Consortium’s progress on understanding, controlling, and detecting
ultrafast electron transport in and between materials composed of
single atomic layers. In these ultimately thin solids, electron transport
is truly two dimensional. Using ultrafast laser techniques, we studied
ballistic, diffusive, and spin/valley-polarized transport of electrons in
two-dimensional materials such as phosphorene, tungsten disulfide,
and rhenium disulfide. The group has also investigated ultrafast electron
transport across van der Waals interfaces between two monolayers, such
as graphene - tungsten disulfide, molybdenum disulfide – molybdenum
diselenide, and tungsten disulfide – phosphorene. These studies
revealed fundamental aspects of electron transport on ultimately small
scales in solids.
ABSTRACT: Photo-induced molecular reactions often involve
short-lived intermediate states whose structure is unknown. Imaging
the nuclear geometry in transient excited states remains a challenge
due to the extreme requirements for spatial and temporal resolution.
Ultrafast electron diffraction can in principle simultaneously provide
sufficient temporal and spatial resolution. We use femtosecond
laser pulses to align molecules, and show that the full 3-D structure
of the molecules can be retrieved from the diffraction patterns.
Recent developments have allowed us to capture structures with
femtosecond resolution, which brings us within reach of fully
mapping the evolution of transient states during a chemical reaction..
BIO: Hui Zhao obtained his PhD in 2000 from Beijing Jiaotong
University. After postdoc trainings at Karlsruhe Institute of Technology
(Germany) and University of Iowa, he joined University of Kansas
in 2007 as an Assistant Professor in Physics, and was promoted to
Associate Professor in 2012. At KU, he developed an ultrafast laser
program to study novel transport phenomena in semiconductors. His
current research interests are optical and electronic properties of twodimensional materials and the heterostructures.
6
BIO: Martin Centurion is an Associate Professor in the Department
of Physics and Astronomy at the University of Nebraska-Lincoln. He
received his Ph.D. in Physics from Caltech in 2005, where he studied
ultrafast holography and nonlinear optics. After a one-year postdoc at
Caltech, he received a Humboldt postdoctoral fellowship to join the
Max Planck Institute of Quantum Optics in Garching, Germany. In
2009 he joined the University of Nebraska as an Assistant Professor.
His current research involves imaging of isolated molecules and
ultrafast molecular dynamics, and the interaction of atoms and
molecules with intense laser fields.
2015 NEBRASKA RESEARCH & INNOVATION CONFERENCE
POSTER PRESENTERS: Ultrafast Dynamics of Atoms, Molecules & Nanostructures
POSTER SESSION BEGINS AT 4:45 P.M.
Applications of Elliptically-Polarized, Few-Cycle Attosecond Pulses 1611
Jean Marcel Ngoko Djiokap, S.X. Hu, L.B. Madsen, N.L. Manakov, A.V. Meremianin, Anthony F. Starace
A new nonlinear dichroic effect is predicted as a first application of our ability to solve the six-dimensional two-electron, time-dependent Schroedinger equation for He
interacting with an elliptically-polarized XUV pulse. Specifically, we demonstrate control of double ionization of He by means of the polarization and carrier-envelope-phase
(CEP) of an intense, few-cycle attosecond XUV pulse. Another application of circularly-polarized attosecond pulses is the production of vortices in photoelectron momentum
distributions.
Attosecond time-resolved streaked photoemission from Mg-covered W(110) surfaces
1612
Uwe Thumm, Q. Liao We formulate a quantum-mechanical model for infrared-streaked photoelectron emission by an ultrashort extreme ultraviolet pulse from adsorbate-covered metal surfaces.
Applying this numerical model to ultrathin Mg adsorbates on W(110) substrates, we analyze streaked photoelectron spectra and attosecond streaking time delays for
photoemission from the Mg/W(110) conduction band and Mg(2p) and W(4f) core levels. Based on this analysis, we propose the use of attosecond streaking spectroscopy
on adsorbate-covered surfaces with variable adsorbate thickness as a method for investigating (a) electron transport in condensed-matter systems and (b) metal-adsorbate
interfacial properties at subatomic length and time scales. Our calculated streaked photoemission spectra and time delays agree with recently obtained experimental data.
Attosecond plasmonic streaking from gold nanospheres
1613
Uwe Thumm, Jianxiong Li
To study time--resolved photoemission from gold nanospheres, we developed a semi--analytical quantum--mechanical approach. We use Mie theory to analytically calculate
plasmonically enhanced fields near 10 to 200 nm gold nanospheres, driven by intense incident near--infrared (NIR) or visible light pulses. We model the gold conduction band
in based on spherical square well potentials. Our first numerical results for streaked photoelectron spectra from gold nanospheres show a 3 times increased streaking spectrum
amplitude for incident 800 nm streaking pulses and 10 nm diameter gold nanospheres, as compared with calculations in which the plasmonic near-field enhancement is
switched off. Supported by the NSF-EPSCOR program.
An Atomic Photoionization Experiment by Harmonic Generation Spectroscopy
1614
Jan Tross, M. V. Frolov, T. S. Sarantseva, N. L. Manakov, K. D. Fulfer, B. P. Wilson, X. Ren, E. D. Poliakoff, A. A. Silaev, N. V. Vvedenskii, Anthony F. Starace, C. A. TralleroHerrero
Measurements of the high-order harmonic generation (HHG) yield of the argon (Ar) atom driven by a strong elliptically-polarized laser field are shown to completely determine
the field-free differential photoionization cross section of Ar, i.e., the energy dependence of both the angle-integrated photoionization cross section and the angular distribution
asymmetry parameter.
Investigation into the differences between incoherent and pulsed white light absorption by nanoparticles in solution
1615
Brandin Davis, J. Powell, S. Zigo, Y. Qin, C. Sorensen, C. Trallero-Herrero
We investigate the difference between absorption spectroscopy done on nanoparticles in solution with incoherent white light and ultrafast pulses of white light. An 800nm, 25
fs, Ti:Saph laser is focused on a CaF2 crystal to produce a coherent white light pulse. The nanoparticle absorption spectrum is subsequently measured.
Anomalous Nonlinear X-ray Compton Scattering
1616
Matthias Fuchs, M. Trigo, J. Chen, S. Ghimire, S. Shwartz, M. Kozina, M. Jiang, T. Henighan, C. Bray, G. Ndabashimiye, P. H. Bucksbaum, Y. Feng, S. Herrmann, G. Carini, J.
Pines, P. Hart, C. Kenney, S. Guillet, S. Boutet, G. J. Williams, M. Messerschmidt, M. M. Seibert, S. Moeller, J. B. Hastings, D. A. Reis
X-ray scattering is typically used as a weak linear atomic-scale probe of matter. At high intensities, such as produced at free-electrons lasers (FELs), nonlinearities can become
important, and the probe may no longer be considered weak. Here we report the observation of one of the most fundamental nonlinear X-ray–matter interactions: the concerted
nonlinear Compton scattering of two identical hard X-ray photons producing a single higher-energy photon. The X-ray intensity reached 4x1020 Watt/cm2 corresponding to an
electric field well above the atomic-unit of strength and within almost four orders of magnitude of the quantum-electrodynamic critical field. We measure a signal from solid
beryllium that scales quadratically in intensity, consistent with simultaneous non-resonant two-photon scattering from nearly-free electrons. The high-energy photons show an
anomalously large redshift that is incompatible with a free-electron approximation for the ground-state electron distribution, suggesting an enhanced nonlinearity for scattering
at large momentum transfer.
Manipulation of Beams of Ultra-relativistic Electrons to Create Femtosecond X-ray Pulses
1617
Jordan ONeal, Austin Schulte, Matthias Fuchs
We develop a compact, laser-driven next-generation X-ray lightsource. To this end, we will use a novel approach that has the potential to shrink the size of high-power X-ray
sources from a typical footprint of more than a dozen football fields to roughly that of a dining room table. The source is expected to generate femtosecond pulses with
~10^9 photons at a photon energy tunable from ~100eV through the water window into the hard X-ray range. We investigate a novel X-ray focusing technique based on the
manipulation of the electron beam during the radiation emission.
2015 NEBRASKA RESEARCH & INNOVATION CONFERENCE
7
POSTER PRESENTERS: Ultrafast Dynamics of Atoms, Molecules & Nanostructures
3-D Molecular Imaging and Dynamics Studied by Ultrafast Electron Diffraction
1618
Jie Yang, Joshua Beck, Cornelis J. Uiterwaal, Martin Centurion
Ultrafast electron diffraction (UED) is a powerful method to study molecular structure and dynamics. For molecules in the gas phase, aligning the molecules break the spherical
symmetry of the angular distribution and making the 3-D imaging possible. In this poster we demonstrate that by combining UED and laser alignment, we were able to achieve
3-D molecular images with atomic resolution. We have also used UED to capture the structure of a transient excited state where we have observed alignment, bond lengthening
and dissociation of carbon disulfide molecules after interacting with an intense laser pulse.
Favorable target positions for intense laser acceleration of electrons in hydrogen-like, highly-charged ions
1619
Liang-Wen Pi, S. X. Hu, Anthony F. Starace
Classical relativistic Monte Carlo simulations of petawatt laser acceleration of electrons bound initially in hydrogen-like, highly-charged ions show that both the angles and
energies of the laser accelerated electrons depend on the initial ion positions with respect to the laser focus. Electrons bound in ions located after the laser focus generally
acquire higher (~GeV) energies and are ejected at smaller angles with respect to the laser beam. Our simulations assume a tightly-focused linearly-polarized laser pulse with
intensity approaching 10^{22}W/cm^2. Up to fifth order corrections to the paraxial approximation of the laser field in the focal region are taken into account. In addition to the
laser intensity, the Rayleigh length in the focal region is shown to play a significant role in maximizing the final energy of the accelerated electrons. Results are presented for
both Ne^{9+} and Ar^{17+} target ions.
Electron Steering With a Low Power Optical Laser 1620
Peter Beierle, Wayne Huang, Roger Bach, Maria Becker, Derek Ruffner, Herman Batelaan
As a beam of 4keV electrons passes by a metallic wall which is illuminated by a laser beam, the electrons experience a force that deflects the beam’s direction by 550microrad
when the electrons are approx. 10 microns from the surface, and as far as 200 microns. This “electron switch” has a response time of approximately 6 microseconds. This
switching mechanism is shown to be robust, as it is demonstrated for various optical wavelengths and surfaces. This type of electronic-free electron manipulation has potential
use in electron beam microscopy (EBM) and electron beam lithography (EBL). In addition, while diffracting a 10keV electron beam through a nanofabricated electron grating,
we observe the effects of illuminating the grating with a laser beam, with inconclusive results which seem to depend on the wavelength of the laser and relative angles between
the grating and the laser beam electron beam.
Compression of Electron pulses for Ultrafast Diffraction Experiments 1623
Omid Zandi, Kyle Wilkin, Alice DeSimone, Jie Yang, Martin Centurion
Non-relativistic highly charged electron pulses are compressed by the time-varying longitudinal electric field of an RF cavity to ultrashort durations for time-resolved electron
diffraction experiments. The compression is done by the synchronization of the cavity’s field to the pulses so that it pushes the front and back sides of each pulse toward each
other. The cavity performance is then evaluated by a streak camera that measures the pulse duration in situ. It consists of a capacitor in parallel to a GaAs photo switch. The
capacitor is initially charged to a high voltage. At the moment the compressed pulse is traversing the capacitor plates, a laser pulse activates the switch resulting in a GHz range
underdamped oscillation of the capacitor electric field. Hence the front and back halves of each pulse see opposite electric fields. This will streak the pulse on the detector with
a length proportional to the pulse duration.
Mega-Electronvolt Ultrafast Electron Diffraction at SLAC and UNL
1624
Matthew Robinson, Jie Yang, Markus Guehr, Theodore Vecchione, Renkai Li, Nick Hartmann, Xiaozhe Shen, Ryan Coffee, Jeff Corbett, Alan Fry, Kelly Gaffney, Tais Gorkhover,
Carsten Hast, Keith Jobe, Igor Makasyuk, Alexander Reid, J. S. Robinson, Sharon Vetter, Fenglin Wang, Stephen Weathersby, Charles Yoneda, Xijie Wang, Alexandra Hotchkiss,
Serge Y. Kalmykov, Bradley Shadwick, Matthias Fuchs, Martin Centurion
Ultrafast electron diffraction (UED) is a rapidly advancing technique, allowing one to study structural changes in molecules during dynamic processes. Yet due technological
limitations, experiments generally struggle to observe dynamics with sub-500 femtosecond time-resolution and sub-Angstrom spatial resolution; the parameters necessary to
resolve individual atomic motions within a molecule during a dynamic process. However, here we present two experiments: one is the fastest UED experiment carried out to
date, with 100 fs RMS time resolution and sub-Angstrom spatial resolution; the other is a newly established plasma accelerated electron source, which will produce high-energy
high-charge pulsed electron beams for UED experiments.
Probing vibrating SF6 with inner-shell photoelectron diffraction
1625
Ngoc Ty Nguyen, Anh Thu Le, Chii-Dong Lin
We present theoretical calculation for photoelectron angular distribution (PAD) from S(2p) in SF6 at low photoelectron energy region below 100 eV. Inner-shell photoelectron
is known to carry information about molecular structure, as it experiences during this half-collision process. We show that it is possible to image very small structural
changes during molecular vibration with PAD near the shape resonance at 13 eV. This is achieved in a pump-probe scheme, in which SF6 is first Raman excited dominantly
to symmetric stretch mode by a relatively short laser pulse and then later probed at different time delays by a soft X-ray pulse of a duration of a few femtoseconds and
photon energy near 200 eV.
8
2015 NEBRASKA RESEARCH & INNOVATION CONFERENCE
POSTER PRESENTERS: Ultrafast Dynamics of Atoms, Molecules & Nanostructures
Single-shot energy- and angular- characteristics of all-laser inverse-Compton x-ray source measured using single-photon spectroscopy 1626
Grigory Golovin, S. Banerjee, K. Brown, S. Chen, D. Haden, C. Liu, J. Mills, C. Petersen, J. Zhang, P. Zhang, B. Zhao, D. Umstadter, M. Veale, M. Wilson
We present spectral and spatial characterization of an all-optical tunable x-ray source based on inverse-Compton scattering. A unique CdTe single-photon-counting
camera was used to measure angular-resolved spectra. The data obtained allowed us to precisely measure central energy, energy spread, and divergence of the scattering
electron beam. A sensitive detection system enabled us to perform the measurements for single laser shots. For the experimental conditions relevant to this work, the
source’s quasi-monoenergetic spectrum was tuned in the energy range 50-110 keV. The source size was measured to be 4±1 um using the knife-edge technique. The
source characteristics and our measurements demonstrate that it is possible to use the inverse-Compton x-ray source to perform single-photon imaging based on k-edge
absorption, x-ray fluorescence, and x-ray diffraction.
Cavity-enhanced optical Hall effect in two-dimensional free charge carrier gases detected at terahertz frequencies
1627
S. Knight, S. Schöche, V. Darakchieva, P. Kühne, C.M. Herzinger, J.A. Woollam, M. Schubert, T. Hofmann
The effect of a tunable, externally coupled Fabry-Pérot cavity to resonantly enhance the optical Hall effect signatures at terahertz frequencies produced by a two-dimensional
electron gases is shown and discussed. Tuning the externally coupled Fabry-Pérot cavity strongly modifies the optical Hall effect signatures, which provides a new degree
of freedom for optical Hall effect experiments in addition to frequency, angle of incidence, and magnetic field direction and strength. We use epitaxial graphene grown by
Si-sublimation on SiC and AlInN/GaN-based high-electron mobility transistor structures on a sapphire substrate as model systems for this experiment.
Electron Dynamics in Nanoparticles Under Intense Laser Fields
1628
Jeffrey Powell, S.J. Robatjazi, A. Vajdu, V. Makhija, X. Li, M.F. Kling, C. Sorensen, A. Rudenko
Nanoparticles bridge the gap between atomic/molecular and bulk matter and, thus, offer unique opportunities to study dynamics of complex systems. Ultrashort laser
pulses provide tools to visualize and, potentially, to control electronic motion in nanoscale objects, nurturing the vision for developing ultrafast, light-driven optoelectronics.
In particular, photoelectron emission from isolated nanosystems pulses can bring insights into their electronic response, local field enhancement and collective excitations
(plasmons).
A Cylindrically Symmetric ‘Micro-Mott’ Electron Polarimeter
1629
Nathan Clayburn, E. Brunkow, G. H. Rutherford, S. J. Burtwistle, T. J. Gay
A small, novel, cylindrically-symmetric Mott electron polarimeter is described. The effective Sherman function, or analyzing power, and the device’s maximum
efficiency have been determined. The new polarimeter’s performance is compared to published results for similar compact retarding-field Mott polarimeters.
SIMION electron trajectory simulations incorporating calculations of Sherman function are presented to explain the differences in performance between
this new Mott polarimeter and previous designs. This polarimeter will be used to measure the polarization of a new, potentially fast source of electrons.
Funded by NSF PHY-1206067 and EPSCoR IIA-1430519
Development of flexible electron time of flight for ultrafast pulse characterization
1630
Pratap Timilsina, P. Mundine, C.Trallero-Herrero
We develop an electron time of flight (eTOF) to characterize ultrafast (femtosecond, sub-femtosecond & attosecond) electric field pulses ranging from the far IR to the
XUV. By measuring the photoelectrons in the presence of two electric fields and their quantum interference we will be able to extract the amplitude and phase of the
electric field. For XUV pulses these are the well-known streaking and RABITT (Reconstruction of Attosecond Beating by Interference of Two-Photon Transition) methods.
The eTOF is based on a set of tunable electrostatic lenses and is capable of measuring 0-150 eV electrons. In addition we can selectively increase the photoelectron yield in
different energies of the spectrum. The precise tuning of electrostatic lens system is done with a Genetic Algorithm with an intensity fluctuation discriminator in the fitness.
State-selective photoexcitation and molecular dissociation using XUV pump – Near-infrared probe
1631
Kanaka Raju Pandiri, Y. Malakar, W. L. Pearson, B. Kaderiya, Xiang Li, D. Trabert, F. Wilhelm, Wei Cao, I. Ben-Itzhak, A. Rudenko
Attosecond light sources based on high-harmonics generation are employed to study time-resolved dynamics. These broadband light sources populate superposition of
states in the system. In contrast, we used narrow bandwidth XUV pulses to achieve state-selective excitation. The experiment is performed with 11th harmonic pump (100
fs, ∼17.3 eV, 200 meV bandwidth) and 800-nm probe pulse sequence to induce the dissociative ionization of O2, which was characterized by energy- and angle-resolved
photoion and photoelectron detection. The observed data can be understood in terms of the (net) absorption of one and two 800-nm photons by the XUV-excited ionic
state.
This project is supported by the Chemical Science, Geosciences, and Bio-Science Division, Office of Basic Energy Science, Office of Science, U.S. Department
of Energy. K.R.P. supported by National Science Foundation Award No. IIA-1430493.
2015 NEBRASKA RESEARCH & INNOVATION CONFERENCE
9
POSTER PRESENTERS: Ultrafast Dynamics of Atoms, Molecules & Nanostructures
Spin Transfer of Quantum Information between Majorana Modes and a Resonator
1632
Alexey Kovalev
This work shows that resonant coupling and entanglement between a mechanical resonator and Majorana bound states can be achieved via spin currents in a 1D quantum
wire with strong spin-orbit interactions. The bound states induced by vibrating and stationary magnets can hybridize, thus resulting in spin-current induced 4Ï€-periodic
torques, as a function of the relative field angle, acting on the resonator. We study the feasibility of detecting and manipulating Majorana bound states with the use of
magnetic resonance force microscopy techniques.
Progress towards a femtosecond, spin-polarized electron source
1633
Maria Becker, Herman Batelaan, Eric Jones, Tim Gay, Evan Brunkow, Nathan Clayburn, Susan Enders, Omid Zandi
Previous and ongoing experiments involving the interaction of femtosecond laser pulses with GaAs crystals are aimed at developing an ultrafast source of spin-polarized
electrons. Experimental studies, including a heuristic model for the unexpected result of subadditivity in pump-probe measurements, will be presented that indicate
electron emission from GaAs occurs at a sub-picosecond time scale. When realized, the ultrafast, spin-polarized electron source will be used for fundamental physics
studies, including electron-electron dynamics in two-particle quantum interference effects such as the Hanbury-Brown Twiss effect. Progress towards this study has
included production of double tips for coherent electron emission.
Nanoantennas and metasurfaces to enhance light-matter interactions at nanoscale 1634
Christos Argyropoulos
Nanoantennas and metasurfaces can manipulate the electromagnetic radiation in unprecedented ways and at nanoscale regions. Metals or high index dielectrics can be
used to build these nanophotonic systems. The large field enhancement in the vicinity of these systems due to localized or collective resonances ensures a significant
boosting of optical nonlinear effects, spontaneous emission rates, and other quantum effects. In addition, two dimensional materials, such as MoS2 and graphene, can be
integrated in these resonating systems. Several future integrated nanophotonic systems are envisioned with the proposed hybrid nanostructures, such as tunable optical
sensors and efficient electro-optical modulators with compact footprint.
Multiphoton dissociative ionization of CS^+
1635
Jyoti Rajput, Bethany Jochim, M. Zohrabi, K. J. Betsch, U. Ablikim, Ben Berry, T. Severt, Peyman Feizollah, A. M. Summers, Kanaka Raju P., G. S. J. Armstrong, B. D. Esry,
K. D. Carnes, I. Ben-Itzhak
We have studied the dissociative ionization of a CS+ molecular-ion beam in the strong-field regime using ~790 nm, ~30 fs laser pulses. A coincidence three-dimensional
momentum imaging method was used to measure all ions and neutrals formed during this multiphoton process. Two prominent channels were observed: charge-symmetric
dissociation, yielding C^+ + S^+, and charge asymmetric dissociation, yielding C + S^(2+). The unusual angular distribution for the charge-symmetric dissociation channel
will be discussed in light of the population of metastable states in the transient CS^(2+) molecular ion.
Velocity-map imaging and streaked photoelectron emission from metallic nanostructures
1636
Erfan Saydanzad, Saydanzad, Erfan, Uwe Thumm
Attosecond time-resolved XUV-pump–IR probe spectroscopy has been shown to be a powerful method for investigating the electron dynamics in atom, and this technique
is now being transferred to the investigation of electronic excitations, electron propagation, and collective electronic (plasmonic) effects in solids[1,2]. Based on classical
trajectory calculations, we simulated (i) the final photoelectron velocity distribution in order to provide observable velocity-map images for gold nanospheres of 10 and
100 nm diameter and (ii) streaked photoemission spectra. By analyzing our numerical results, we illustrate how spatio-temporal information about the sub-IR-cycle
plasmonic and electronic dynamics is encoded in velocity-map images and streaked spectra. *Supported by the NE/KS NSF-EPSCOR program.
[i] Attosecond physics: attosecond streaking spectroscopy of atoms and solids, U. Thumm, Q. Liao, E. M. Bothschafter, F. Süßmann, M. F. Kling, and R.
Kienberger, p. 387, Handbook of Photonics, Volume 1, (Wiley, 2015).
[ii] Attosecond time-resolved streaked photoemission from Mg-covered W(110) surfaces, Q. Liao and U. Thumm, Phys. Rev. A 92, 031401(R) (2015).
Progress Towards Large Flux High-Order Harmonic Generation Driven by Two-Color Laser Fields
1637
Travis Severt, J. Tross, P. Timilsina, S. Buczek, C. Trallero-Herrero, I. Ben-Itzhak
In the past decade, there has been a push to create bright tabletop XUV sources to study ultrafast dynamics in atoms and molecules. One of the more promising
techniques is high-harmonic generation (HHG) driven by two-color laser fields. Our first step towards this goal is to investigate HHG from argon in an 800/400-nm
laser field. In preliminary data, we observe two orders of magnitude increase for most harmonics created by the two-color field, and almost a three orders of magnitude
enhancement of the ninth harmonic, when compared to the single-color (800-nm) field.
10
2015 NEBRASKA RESEARCH & INNOVATION CONFERENCE
POSTER PRESENTERS: Ultrafast Dynamics of Atoms, Molecules & Nanostructures
Strong-field dissociation dynamics of molecular dications
1638
Bethany Jochim, T. Severt, M. Zohrabi, U. Ablikim, Ben Berry, B. Gaire, K. J. Betsch, F. Anis, K. D. Carnes, B. D. Esry, I. Ben-Itzhak
We study the dissociation dynamics of metastable molecular dications, NO2+, CS2+, and CO2+ (several-keV beam targets), driven by intense ultrafast laser pulses. In
NO2+, time-dependent Schrodinger equation calculations and measured angular distributions demonstrate the importance of multiphoton permanent dipole transitions.
Similar permanent dipole transitions are experimentally observed in CS2+ dissociation. In CS2+, we also find dissociation involving no energy gain (or loss) from the field
due to a pump-dump-like process driven by a single laser pulse. This phenomenon is also observed in CO2+, whose ground electronic state has structure similar to that of
CS2+.
Carrier-envelope phase control over fragmentation of H2+ and D2
1639
Bethany Jochim, M. Zohrabi, B. Berry, Nora G. Kling, Bethany Jochim, T. Severt, U. Ablikim, K. J. Betsch, S. Zeng, F. Anis, Z. Wang, M. F. Kling, K. D. Carnes, B. D. Esry,
I. Ben-Itzhak
We examined carrier-envelope phase (CEP) dependences in H2+ dissociation and Rydberg D* formation from D2. D* formation exhibits strong CEP dependences in the
total yield, and both molecules show CEP-dependent asymmetries in the fragment emission direction with respect to the laser polarization. These observations result from
interfering pathways involving different numbers of photons and are consistent with the general CEP theory [1]. Moreover, D* spatial asymmetry and yield exhibit higherorder oscillations related to a higher difference in the number of photons involved in the interfering pathways.
[1] V. Roudnev and B. D. Esry, Phys. Rev. Lett. 99, 220406 (2007)
A 600 MW light source at 7 micrometer center wavelength as a path to strong field science in the far infrared
1640
Derrek Wilson, Carlos Trallero-Herrero
We demonstrate a far infrared source (7 micrometer) with pulse duration of ~ 130 fs and pulse energies of 80 mJ. This source was generated by performing difference
frequency generation on the Signal and Idler pulses from an Optical Parametric Amplifier. We show a clear path to achieving 1 GW peak power and applications of this light
source to strong field science in both atoms and solid systems.
Study of Nuclear Wave Packet Dynamics in Strong-Field Ionized Iodomethane and Diiodomethane 1641
Yubaraj Malakar, Balram Kaderiya, Wright Lee Pearson, Kanaka Raju Pandiri, Mohammad Zohrabi, Farzaneh Ziaee, Itzik Ben-Itzhak, Daniel Rolles, Artem
Rudenko
As a prototypical polyatomic system with well-studied photodissociation dynamics, the iodomethane molecule (CH3I) has recently been used to test novel quantum
control schemes and to investigate charge transfer processes after X-ray absorption. Here we present the results of Infra-Red pump-probe experiment that maps bound
and dissociating nuclear wave-packets in singly and doubly charged CH3I ionic states. Measuring dependence of energies and yields of ionic fragments on time-delay
between two 25fs, 800nm pulses, we track the propagation of different dissociation pathways and vibrational motion of the molecule. We employ the same experimental
technique to study nuclear wave-packet dynamics in diiodomethane (CH2I2).
Pump-probe Sub-additivity in Photoelectron Emission from GaAs 1642
Evan Brunkow, Nathan B. Clayburn, Maria Becker, Eric Jones, Herman Batelaan, T.J. Gay
Using a 75 ns pulsed laser (800 nm center wavelength; 10 nJ/pulse), we have shown that photoemission from GaAs induced by coherent pump and probe pulses is more
than additive for delays < 200 fs. This implies that the emission is slower than 200 fs or that other dynamics that affect the photoemission are operative [1]. For delays
between 0.5 and 16 ps, the electron emission is sub-additive. This appears to be the result of the reflectance changing due to the first pulse, which reduces the absorption
of the second pulse. The results of experiments studying this sub-additivity are presented.
Funded by NSF PHY-1206067, EPSCoR IIA-1430519, and NSF 1306565 (HB)
[1] E. Brunkow et al., Bull. Am. Phys. Soc. 59 (2014).
Progress report on laser control of electrons in nanostructures
1643
Eric Jones, Gobind Basnet, Maria Becker, Evan Brunkow, Nate Clayburn, Peter Beierle, Bret Flanders, Tim Gay, Herman Batelaan
Laser-induced field emission tips are the standard for ultrafast electron microscopy and diffraction, capable of delivering single-electron pulses of femtosecond duration
with picometer resolution. We investigate the electron emission from two modified tip sources: a gold (Au) nanowire, and a GaAs tip. Electron emission from the Au
nanowire may give insight into the internal electron dynamics in and on the wire. Controlling those dynamics could allow for single- or multi-electron pulses on demand.
The GaAs tip may be a novel ultrafast source of spin-polarized electrons. Other nanostructures under investigation include nanofabricated gratings and plasmonic antenna
arrays for free-electron control. 2015 NEBRASKA RESEARCH & INNOVATION CONFERENCE
11
POSTER PRESENTERS: Ultrafast Dynamics of Atoms, Molecules & Nanostructures
Field-Enhanced Chemical Reactions: Photochromic Switching in the Plasmonic Field of Gold Nano-Structures 1644
Christopher Otolski, Ryan Hamelin, Christopher G. Elles
The photochromic ring-opening and ring-closing reactions of a diarylethene derivative in the solid phase proceed readily following resonant excitation of the molecule.
Molecules deposited onto an array of gold nanorods undergo the same reaction through non-resonant excitation due to the interaction of the molecules with the
plasmonic field of the nanostructured array. Plasmonic field enhancement allows non-resonant switching with very low intensity irradiation at wavelengths that are not
resonant with the absorption bands of the molecule. Only a fraction of the molecules convert back to the open form under these conditions due to the limited range of
the plasmonic field.
Bond rearrangement and hydrogen migrations in small hydrocarbons through strong-field induced interactions
1645
Wright Lee Pearson, Yubraj Malakar, Artem Rudenko
Imaging and control schemes for photo-induced structural rearrangement dynamics are of particular interest to ultrafast photochemistry. Here we report on a series
of experiments that study bond dissociation and rearrangement of small hydrocarbons (CH4, C2H2, C2H4) irradiated by intense 800nm laser pulses. Different
fragmentation pathways, isomerization and proton migration channels are measured by coincident ion momentum patterns for two- or three-body breakup channels.
Among these studies we observe C2H2 and C2H4 isomerization where the evolution of kinetic energy release spectra with increasing laser pulse duration differentiates
active isomerization pathways within or after the pulse.
Intense-Field Photoionization of Molecules using Ultrashort Radiation Pulses: Carbondisulfide and Substituted Monoaromatic Hydrocarbons 1646
Joshua Beck, Timothy Scarborough, Cornelis J. Uiterwaal
We experimentally investigate the intense-field photodynamics of molecules using 50-fs, 800-nm pulses with in-tensities of 1012 to 1014 W/cm2. Target molecules include
carbondioxide (CO2), carbondisulfide (CS2), and substi-tuted monoaromatics, such as aniline (C6H5-NH2) and nitrobenzene (C6H5-NO2). We use mass spec-trometry to
detect ions, and avoid focal intensity averaging. For CS2, the onset of ionization is dominated by parent ions (1+, 2+). We show that ionization is insignificant for intensities
that maximize alignment of CS2, which validates ultrafast electron diffraction experiments from aligned CS2. For the substituted monoaromatics we discuss the role of
the substituent.
12
2015 NEBRASKA RESEARCH & INNOVATION CONFERENCE

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