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Abstract Booklet

Workshop on Ultrafast Electron Sources for Diffraction and Microscopy Applications

December 12-14, 2012

University of California, Los Angeles

Workshop on Ultrafast Electron Sources for Diffraction and Microscopy Applications December 12-14, 2012

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Recent years have witnessed tremendous progress in our understanding of the ultrafast and ultrasmall world thanks to the development of ultrafast optical lasers and the advent of X-ray Free Electron Laser (XFEL). Other approaches that utilize electrons as a probe have been demonstrating in smaller scale setups capabilities complementary to X-ray based techniques. Electron based techniques enjoy many unique advantages, such as large interaction cross-section, compact size and cost effectiveness. The development of high-brightness electron sources directly led to the success of XFEL; and at the same time, such high-brightness sources have opened the door to the direct investigation of the physical, chemical and biological dynamics processes with atomic spatial and temporal resolution by Ultrafast Electron Diffraction and Microscopy.

The near term future promises further exciting developments as many schemes have been recently proposed and experimentally demonstrated to improve temporal resolution in electron-based material studies. These include raising the energy to MeV levels, RF and magnetic bunch compression, laser-plasma electron sources, and RF streak diffraction mode. In transmission electron microscopy, the introduction of aberration and chromatic corrections has allowed TEMs to achieve unsurpassed spatial resolution. The addition of ultrafast temporal resolution is the next frontier in electron microscopy.

In this framework we would like to hold a workshop at UCLA, and invite all groups involved in ultrafast electron sources to help our growing community define what are the limitations and the potentials opened by such novel techniques. The workshop objectives are to inform the broad scientific communities – accelerator, electron scattering and ultrafast science, the latest development in ultrafast electron sources, and to identify critical technologies and high impact scientific opportunities. The issues we would like to address at the workshop: which of the beam characteristics need to be further improved? What processes or material studies will take most advantage from the unique properties of the source? What are the limits (and the requirements) in temporal resolution?

The connections with the conventional ultrafast structural dynamics investigation tools like conventional ultrafast electron diffraction, transmission electron microscopes as well as the complementarities with the x-ray diffraction and imaging communities will be also explored.

Topics include: Beam sources for Ultrafast Electron Diffraction. RF guns, laser-plasma based injectors,

DC photoguns. Compression methods: Magnetic, RF structures. Timing. Synchronization. Jitter control. Samples. Liquid, gas and solid phases. Electron Damage.


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Detectors and Diagnostics. Strong electron lenses. Imaging mode. Electron Microscopy. Scientific opportunities.

Organizing Committee: P. Musumeci (UCLA), X. J. Wang (BNL), R. K. Li (UCLA) Science Advisory Committee: J. Rosenzweig (UCLA), J. Spence (ASU), A. Zewail (Caltech), J. Zhang (Shanghai JiaoTong University), Y. Zhu (BNL) Program Committee: P. Baum (LMU), J. Cao (FSU), F. Carbone (EPFL), M. Chen (Tohoku University), R. Falcone (UC Berkeley), J. Hastings (SLAC), H. Ihee (KAIST), J. Luiten (TU/e), B. Reed (LLNL), B. Siwick (McGill University), C.X. Tang (Tsinghua University)


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Wednesday, Dec. 12th 2012 8:00-9:00 Registration and Breakfast 9:00-9:10 Opening 9:10-9:40 Scientific Opportunities with Ultrafast Electron Diffraction and Microscopy

J. Cao (Florida State Univ.) 9:40-10:10 State of Art of Electron Microscopy and Future challenges

L. Fitting Kourkoutis (Cornell Univ.) 10:10-10:40 Coffee break 10:40-11:05 Femtosecond electron diffraction: heralding the era of atomically-resolved

dynamics G. Sciaini (DESY and Univ. of Hamburg)

11:05-11:30 MeV UED and Its Applications for Correlated Material Studies P. Zhu (BNL and Shanghai Jiaotong Univ.)

11:30-11:55 REGAE: RF photoinjector based UED at DESY S. Manz (DESY)

11:55-12:10 Lattice response to femtosecond laser excitation of Nickel studied by time resolved transmission electron diffraction C. Streubühr (Univ. of Duisburg-Essen)

12:10-12:25 Snapshot imaging of Electron Pulse Dynamics for High-Brightness Ultrafast Diffraction and Microscopy Z. Tao (Michigan State Univ.)

12:25-13:30 Lunch 13:30-13:55 Movie Mode Dynamic Transmission Electron Microscopy

B. Reed (LLNL) 13:55-14:20 Granularity effects in high-brightness electron beams

B. van der Geer (TU/e/Pulsar Physics) 14:20-14:45 Four-dimensional electron tomography

O.-H. Kwon (Caltech) 14:45-15:00 Proposed Addition of Ultra-fast Imaging Capabilities to Sandia’s In-situ Ion

Irradiation TEM K. Hattar (Sandia National Laboratory)

15:00-15:20 Discussion: Beam requirements for ultrafast microscopy applications 15:20-15:40 Coffee break 15:40-17:30 Poster session, wine reception, and Pegasus Lab tour 17:30 Dinner on your own


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Thursday, Dec. 13th 2012

8:00-9:00 Breakfast 9:00-9:25 MeV electron diffraction and microscopy in Osaka University

J. Yang (Osaka Univ.) 9:25-9:50 Ultrafast electron diffraction with radio-frequency compressed electron

pulses B. J. Siwick (McGill Univ.)

9:50-10:05 Plans of UED experiments at the X-Band Test Area C. Limborg-Deprey (SLAC)

10:05-10:20 Ultrafast diffraction with single electrons F. Kirchner (LMU)

10:20-10:40 Discussion: Comparison between compressed DC and RF guns 10:40-11:00 Coffee break 11:00-11:25 Sub-fs-precision, ultrafast laser-based optical and microwave timing and

synchronization J. Kim (KAIST)

11:25-11:50 Femtosecond synchronization of lasers and electron beams J. Byrd (LBNL)

11:50-12:05 Radiofrequency phase space manipulation of ultrashort electron beams J. Luiten (TU/e)

12:05-12:20 Innovative Low-Energy Ultra-Fast Electron Diffraction (UED) System L. Faillace (RadiaBeam Technologies)

12:20-12:30 Discussion: Limits in timing and temporal resolution 12:30-13:30 Lunch 13:30-13:55 Ultrafast ultracold electron bunches and space-charge effects in cold ion

bunches R. Scholten (Univ. of Melbourne)

13:55-14:20 Ultrashort electron beams from laser gated tips P. Hommelhoff (Univ. of Erlangen and MPQ)

14:20-14:35 Application of laser-triggered nanometer-sized electron sources in ultrafast low-energy electron diffraction and ultrafast transmission electron microscopy S. Schäfer (Univ. of Göttingen)

14:35-14:50 Field Emission and Channeling Radiation for High-Spectral-Brilliance X-Ray Sources


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C. Brau (Vanderbilt Univ.) 14:50-15:10 Discussion: Where advanced sources can help? Ultimate limit in brightness. 15:10-15:30 Coffee break 15:30-15:55 Ultrafast electron sources based on plasmas produced by intense

femtosecond laser pulses S. Sakabe (Kyoto Univ.)

15:55-16:20 Toward a high quality electron source from a laser wakefield accelerator for electron diffraction J. Faure (LOA)

16:20-16:35 Ultrashort electron source from laser-plasma interaction J. Liu (SIOFM, CAS)

16:35-16:50 Concept for femtosecond point-projection imaging of nanostructures with coherent low-energy electron pulses M. Müller (Fritz-Haber-Institut)

16:50-17:05 m*: A route to ultra-bright photocathodes A. Schroeder (Univ. of Illinois at Chicago)

17:05-17:25 Discussion: Where advanced sources can help? Ultimate limit in brightness. 18:00 Banquet at the UCLA Faculty Center

Friday, Dec. 14th 2012

8:00-9:00 Registration and Breakfast

9:00-9:25 Ultrafast Gas Electron Diffraction M. Centurion (Univ. of Nebraska-Lincoln)

9:25-9:50 Liquid Jets for Ultrafast Diffraction Experiments U. Weierstall (Arizona State Univ.)

9:50-10:05 Designing in-situ experiments in gas and liquid environments for the DTEM P. Abellan (PNNL)

10:05-10:20 Time-resolved gas electron diffraction - building a new apparatus in Edinburgh D. Wann (Univ. of Edinburgh)

10:20-10:40 Coffee break 10:40-11:05 Photoelectron Pulse Properties from Free-Free Transitions in Ultrafast

Transmission Electron Microscopy D. Flannigan (Univ. of Minnesota)

11:05-11:30 Near Field 4D Electron Microscopy S. T. Park (Caltech)


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11:30-11:45 Ultrafast Processes on Surfaces Studied by Time-Resolved Reflection High Energy Electron Diffraction T. Frigge (Univ. of Duisburg-Essen)

11:45-12:00 Determination of Directional Atomic Displacement from Femtosecond Laser Excited Bismuth in Time Resolved Electron Diffraction P. Zhou (Univ. of Duisburg-Essen)

12:00-12:30 Applications of ultrafast electron diffraction C. Y. Ruan (Michigan State Univ.)

12:30 Closing of the Workshop 13:30 Pegasus Lab tour

Poster Session

1. A High Repetition rate-high brightness electron source for Time-Resolved electron diffraction and microscopy D. Filippetto, F. Sannibale, M. Zolotorev (Lawrence Berkeley National Laboratory)

2. Collimated Quasi-monoenergetic Electron Emission at locked phases from the Laser-Driven Surface Plasma Wave Y. Tian (Shanghai Institute of Optics and Fine Mechanics, Chinese Academy of Sciences)

3. Complex Acoustic Waves in Graphite Observed by Convergent-Beam Ultrafast Electron Crystallography W. Liang (Cal Tech)

4. Continuous MeV Electron Diffraction using a Flat Electron Beam F. Fu, R. Li, X. Wang and D. Xiang (Shanghai Jiao Tong University, SLAC National Accelerator Laboratory, UCLA, Brookhaven National Laboratory)

5. Controlled molecules for time-resolved electron Diffraction Experiments N. Mueller (Center for Free-Electron Laser Science, DESY and University of Hamburg)

6. Design and Implementation of a Flexible Beamline for FS Electron Diffraction Experiments G. Mancini (LUMES – EPFL)

7. Development of High Brightness Electron Source Laboratory at Fermilab


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H. Panuganti (Northern Illinois University)

8. Development of Hybrid Gun for the High Brightness Beam Generation A. Fukasawa, S. K. Mahapatra, H. To, B. Baumgartner, J. B. Rosenzweig, P. Musumeci, R. Li, UCLA, CA, USA David Alesini, Luca Ficcadenti, Bruno Spataro, INFN/LNF, Frascati, Italy A. Valloni, Luigi Palumbo, Rome University La Sapienza, Rome, Italy

9. Dispersion Compensation for Attosecond Electron Pulses M. Centurion (University of Nebraska – Lincoln)

10. High Brightness Sub-picosecond Electron Pulse Generation J. Li (East China Normal University, State Key Laboratory of Precision Spectroscopy)

11. Multi-Objective Molecular Dynamics Simulations with the GPT Code B. van der Geer (Pulsar Physics)

12. Time Resolved Electron Diffraction on Nanomaterials P. Zhou (Faculty of Physics, University of Duisburg-Essen)

13. Ultracold and Ultrafast Electrons Diffracted from Graphene E. Vredenbregt (Eindhoven University of Technology)

14. Ultrafast Time Resolved Surface Sensitive Electron Diffraction with Tilted Pump Pulse Fronts C. Streubühr (Faculty of Physics, University of Duisburg-Essen)


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Scientific Opportunities with Ultrafast Electron Diffraction and Microscopy

Presenter: J. Cao (Florida State Univ.)

In the past ten years, we have witnessed rapid advancement of ultrafast electron

diffraction and microscopy. In many cases, these techniques have demonstrated

the unprecedented capability of directly probing the dynamical processes at the

relevant atomic time and length scales, thus providing new scientific

opportunities in the fields of biology, chemistry, physics, and materials science.

This talk will highlight some of these recent development and applications as well

as some future perspectives.


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State of Art of Electron Microscopy and Future challenges

Presenter: L. Fitting Kourkoutis (Cornell University)

L. Fitting Kourkoutis, J. A. Mundy, D. A. Muller*

School of Applied and Engineering Physics, Cornell University, Ithaca, NY 14853

*Kavli Institute at Cornell for Nanoscale Science

Atomic-resolution spectroscopic imaging in state-of-the-art electron microscopes is now capable of unraveling bonding details at buried interfaces and clusters, providing both physical and electronic structure information [1]. The thousand-fold increase in electron energy loss spectroscopy (EELS) mapping speeds over conventional microscopes allows us to collect data from millions of spectra. In complex electronic materials interfaces and defects can dramatically change the macroscopic properties of the system. Using spectroscopic imaging microscopic inhomogeneities, atomic-scale interdiffusion and bonding changes can now readily be characterized and correlated with the macroscopic properties of the structure [2]. [1] D. A. Muller, L. F. Kourkoutis, M. Murfitt, J. H. Song, H. Y. Hwang, J. Silcox, N. Dellby, O. L. Krivanek, Science 319, 1073 (2008). [2] L. F. Kourkoutis, J. H. Song, H. Y. Hwang, D. A. Muller, Proc. Natl. Acad. Sci. 107, 11682 (2010).


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Femtosecond Electron Diffraction: Heralding the Era of Atomically-Resolved Dynamics

Presenter: G. Sciaini (DESY and University of Hamburg)

One of the great dream experiments in Science is to directly observe atomic

motions as they occur. Femtosecond electron diffraction provided the first ‘light’

of sufficient intensity to achieve this goal by attaining atomic resolution to

structural changes on the relevant timescales. During my talk I will cover the

technical progress that made this new level of acuity possible and give a survey of

the new insights gained from an atomic level perspective of structural dynamics1.

Thermally and purely electronically driven atomic displacements are going to be

discussed as well as phenomena involving strongly correlated charge density

wave systems. I will finalize my talk showing recent results obtained for an

organic crystal composed by light scattering centers. Here, we implemented a

recently developed ultra-bright femtosecond electron source to obtain an

atomically-resolved map of the relevant molecular motions driving the photo-

induced insulator-to-metal phase transition in the organic charge-transfer salt

(EDO-TTF)2PF6. This study is the first in its kind and illustrates the potential of

ultra-bright femtosecond electron sources to provide new insights into complex

dynamical phenomena relevant to chemistry and biology.


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MeV UED and Its Applications for Correlated Material Studies

Presenter: P. Zhu (BNL and Shanghai Jiaotong University)

MeV electron diffraction with a 100-fs time resolution and 5-fC single-shot-

imaging sensitivity has been experimentally demonstrated. The MeV-UED has

been successfully employed to study ultrafast melting of charge-density-wave in

TaSe2 and orbit-order dynamics in La.5Sr1.5MnO4.


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REGAE: RF Photoinjector Based UED at DESY

Presenter: S. Manz (DESY)

S. Manz1, D. Zhang1, A. Casandruc1, J. Hirscht1, S. Bayesteh3, S. Keskin1, M. Felber2, J. Nicholls4, F. Mayet3, M. Hachmann3, T. Gehrke3, S. Jangam1, A. Marx1, S. Hayes1,

K. Pichugin1, H. Delsim-Hashemi2, H. Schlarb2, M. Hoffmann2, M. Huening2, G. Moriena4, G. Sciaini1, M. Hada1, K. Floettmann2, R. J. Dwayne Miller1, 4

1 Max Planck Research Department for Structural Dynamics, University of Hamburg, CFEL, Luruper Chaussee 149, 22761 Hamburg, Germany

2 DESY Hamburg, Notkestrasse 85, 22607 Hamburg, Germany

3 Institute of Experimental Physics, CFEL, Luruper Chaussee 149, 22761 Hamburg, Germany

4 Departments of Chemistry and Physics, University of Toronto, Toronto, Ontario M5S 3H6, Canada

The relativistic electron gun for atomic exploration (REGAE) has been designed to

study structure and dynamics in a wide range of systems. Aiming for a time

resolution of far less than 100 fs, we plan to observe fast structural changes in

solid, solution and gas phase with single-shot femtosecond electron diffraction in

the energy range from 2 – 5 MeV. The presentation will describe the

experimental setup and report on the current status of static electron diffraction.

The feasibility of performing real space imaging with REGAE will be discussed as

well.


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Lattice Response to Femtosecond Laser Excitation of Nickel Studied By Time Resolved Transmission Electron Diffraction

Presenter: C. Streubühr (Univ. of Duisburg-Essen)

Ferromagnetic Nickel is widely studied in ultrafast magnetism, and direct

information on the femtosecond lattice dynamics is required. Here will present an

ultrafast transmission electron diffraction study of the lattice response of thin

free-standing Nickel single-crystalline films. The time-dependent diffraction

intensities were analyzed and are found to be inconsistent with simple lattice

heating. This yet unaccounted disagreement between the experimental results

and an explanation in terms of simple lattice heating will be shown.


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Snapshot imaging of Electron Pulse Dynamics for High-Brightness Ultrafast Diffraction and Microscopy

Presenter: Z. Tao (Michigan State Univ.)

We present the methods and results employing the shadow projection imaging

technique to directly interrogate the space charge effects of the ultrashort,

intense photoelectron pulses shortly after photoemission and during the free-

space expansion in a dc photo-gun geometry. Combined with analytical Gaussian

model and ab initio three-step photoemission model with fast multipole method,

we elucidate several essential space-charge-led features. The agreements

between theoretical models and experimental results enable us to understand

the non-linear effects in space charge dynamics and evaluate its impacts on the

performance of the next generation high-brightness ultrafast electron diffraction

and imaging systems.


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Movie Mode Dynamic Transmission Electron Microscopy

Presenter: B. Reed (LLNL)

The dynamic transmission electron microscope (DTEM) combines pulsed lasers

with a modified TEM column to capture the details of fast, irreversible processes

in materials. Specifically, the DTEM is designed to capture a complete real-space

image in a single nanosecond-scale exposure. This has revealed previously

invisible details of phase transformations, microstructural evolution, and solid-

state chemical reactions. A recent upgrade the LLNL DTEM yielded a new "movie

mode" capability, which captures 9 independent real-space images or diffraction

patterns in the space of a few microseconds, thus enabling an entirely new class

of experiments including the quantification of individual nucleation and growth

events.


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Granularity effects in high-brightness electron beams

Presenter: B. van der Geer (TU/e/Pulsar Physics)

Electron sources based on laser-cooling and trapping techniques are a relatively

new reality in the field of charge particle accelerators. The dynamics of these

sources are governed by stochastic effects, and not by the usually dominant

space-charge forces. As the high-brightness field moves towards increasingly

higher brightness, these stochastic effects will play an increasingly important role.

In this presentation I will discuss the physics of these granularity effects and show

their effect using molecular dynamics simulations with the GPT code where we

track each and every particle in realistic fields and including all pair-wise

interactions.


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Four-dimensional electron tomography

Presenter: O.-H. Kwon (Caltech)

Electron tomography provides three-dimensional (3D) imaging of equilibrium

structures of materials and biological specimens. Here, we present the

development of 4D electron tomography by integrating the fourth dimension

(time resolution) with the 3D spatial resolution obtained from a tilt-series of 2D

projections of an object. The methodology utilizes the ultimate spatiotemporal

resolution of ultrafast electron microscopy, in which femtosecond electron pulses

are chirped [1]. A series of time-framed tomograms constitute a movie, thus,

enabling the studies of transient structures, as demonstrated with carbon

nanotubes of various modes of vibration [2]. Also presented is stereographic

imaging, in analogy to 4D electron tomography, for a nanostructure in

complicated motion [3]. References [1] S. T. Park, O.-H. Kwon, A. H. Zewail, New J.

Phys. 14, 053046 (2012).[2] O.-H. Kwon, A. H. Zewail, Science 328, 1668 (2010).[3]

O.-H. Kwon, H. S. Park, J. S. Baskin, A. H. Zewail, Nano Lett. 10, 3190 (2010).


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Proposed Addition of Ultra-fast Imaging Capabilities to Sandia’s In-situ Ion Irradiation TEM

Presenter: K. Hattar (Sandia National Laboratory)

Understanding the nucleation and interactions of various radiation defect

structures is essential to predicting the performance of systems ranging from

satellites to nuclear power plants. Sandia National Laboratories’ Ion beam Lab has

recently developed an in situ ion irradiation transmission electron microscope

that permits real time observation of these interactions. In addition to the

nanoscale resolution permitted by the TEM, a sub-microsecond temporal

resolution is needed to capture the intermediate structures. These intermediate

structures are essential in identifying the active mechanisms present. The

feasibility of such an addition to the current system is currently under research.


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MeV Electron Diffraction and Microscopy in Osaka University

Presenter: J. Yang (Osaka Univ.)

The visualization of fundamental dynamic processes in matter occurring on

femtosecond time scales has attracted much attention in chemistry, material

science and biology. Ultrafast electron diffraction and microscopy (UED and UEM)

provide a real-time observation of structural dynamics in matter by recording the

change in the characteristics of electron diffractions or images in the pump state

and the unpump state. We have developed both a relativistic-energy UED and a

prototype of relativistic-energy UEM using a femtosecond photocathode RF gun.

In this paper, we will report the results of the femtosecond electron bunch

generation in the RF gun, the ultrafast electron diffractions and the first

experiments of relativistic-energy electron imaging.


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Ultrafast Electron Diffraction with Radio-Frequency Compressed Electron Pulses

Presenter: B. J. Siwick (McGill Univ.)

In this talk I will give an overview of ultrafast electron diffraction (UED) using

radio-frequency (RF) compressed electron pulses in the 100keV energy range.

The concepts involved in recompressing femtosecond laser produced electron

bunches with RF cavities will be discussed along with their practical

implementation at McGill University. Novel methods to characterize the

temporal impulse response function in pump-probe geometry using laser fields

and streak cameras will also be described. At pC bunch charges time resolution in

this instrument is ~350 fs FWHM, currently limited by RF/laser synchronization

jitter not the recompressed electron pulse duration which we estimate to be 150

+/- 50 fs FWHM. The instrument performance in UED experiments will be

demonstrated through two examples involving photo-induced structural

dynamics in materials.


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UED Experiments at the X-Band Test Area

Presenter: C. Limborg-Deprey (SLAC)

The XTA is a photoinjector equipped exclusively with X-Band RF accelerator

components, a 5.5 cell gun, a linac and a transverse deflector. Early next year, the

XTA will be modified with minor changes to run UED experiments. A first

experiment will utilize ~ps long electron pulses streaked with the transverse

deflector. The second experiment will utilize ~10 fs electron pulses out of an RF

compressor. Simulations indicate that 3MeV, kA, 10fs rms, 0.2 mrad e-bunches

could be used. The first experiment will give a reference in view of solving the

challenging issue of synchronization/pulse identification met in single shot

experiments.


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Ultrafast Diffraction with Single Electrons

Presenter: F. Kirchner (LMU)

We report on the generation of single-electron pulses for advancing ultrafast

diffraction to the time scale of electronic motion. Tailored excitation of metallic

photocathodes produces single-electron pulses with a minimized dispersion and

divergence. A microwave cavity can be used to further compress the wave

packets in time. ‘Isochronic’ magnetic lenses avoid the temporal distortions

introduced by the imaging system. The transverse coherence of the pulses

exceeds 20 nm, sufficient to cover biomolecular systems. We discuss the

perspectives and possibilities that these advancements may bring about.


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Sub-fs-precision, Ultrafast Laser-Based Optical and Microwave Timing and Synchronization

Presenter: J. Kim (KAIST)

I will introduce the most recent progress in subfemtosecond-precision optical and

microwave timing and synchronization based on ultrafast fiber lasers. The topics

will be (a) the optimization of timing jitter in ultrafast fiber lasers to the sub-fs

regime, (b) the extraction of microwave signals from ultrafast fiber lasers with

sub-fs jitter and stability, (c) long-distance synchronization of remote ultrafast

lasers and microwave sources with sub-10-fs drift maintained more than a week.

The combination of these techniques will culminate in a modular, flexible, sub-fs-

precision timing system for various types of local and remote ultrafast pump-

probe experiments.


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Femtosecond Synchronization of Lasers and Electron Beams

Presenter: J. Byrd (LBNL)

I will describe the development of femtosecond synchronization of electron

beams and ultrafast lasers at the fsec level and the its application to accelerators,

particularly linac-driven free electron lasers. I will then describe how these

techniques might be applied to smaller facilities for ultrafast electron diffraction.


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Radiofrequency Phase Space Manipulation of Ultrashort Electron Beams

Presenter: J. Luiten (TU/e)

The development of ultrafast time-dependent electron optics is required to fully

exploit the potential of ultrashort high-brightness electron beams. We are

investigating various ways to manipulate the 6D phase space distribution of

pulsed electron beams with resonant radiofrequency cavities. Besides bunch

compression, TM-010 cavities may be employed to reduce energy spread and as

time-dependent lenses, allowing correction of spherical aberrations. Deflecting

TM-110 cavities are usually applied for bunch length diagnostics, but may also

serve as fast beam choppers, enabling significant improvements of UEM in

stroboscopic mode. Time-of-flight femtosecond EELS may be realized by the

combination of TM-110 and TM-010 cavities.


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Innovative Low-Energy Ultra-Fast Electron Diffraction (UED) System

Presenter: L. Faillace (RadiaBeam Technologies)

RadiaBeam, in collaboration with UCLA, is developing an innovative, inexpensive,

low-energy ultra-fast electron diffraction (UED) system which allows us to

reconstruct a single ultrafast event with a single pulse of electrons. Time resolved

measurement of atomic motion is one of the frontiers of modern science, and

advancements in this area will greatly improve our understanding of the basic

processes in materials science, chemistry and biology. The high-frequency (GHz),

high voltage, phase-locked RF field in the deflector allows temporal resolution as

fine as sub-100 fs.


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Ultrafast Ultracold Electron Bunches and Space-Charge Effects in Cold Ion Bunches

Presenter: R. Scholten (Univ. of Melbourne)

Cold atom electron and ion sources based on photoionisation of laser-cooled

atoms offer interesting opportunities for diffractive imaging with high transverse

coherence, and investigation of self-field effects. We have demonstrated that

femtosecond excitation can produce electron bunches that are colder than might

be expected given the time-bandwidth limit of the excitation pulses. In separate

work, we have found unusual structures forming during the propagation of ion

bunches that are initially spherically symmetrical. I will describe our results and

models for these phenomena.


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Ultrashort Electron Beams from Laser Gated Tips

Presenter: P. Hommelhoff (Univ. of Erlangen and MPQ)

We will report on a tip based electron source that is optimized to maintain short

electron pulse duration and low emittance. The source is based on a nanometer

sharp tungsten needle tip in 310-orientation on which we focus femtosecond

laser pulses, in combination with a two-anode structure that allows us to

accelerate low charge electron pulses fast to 30 keV. This way, the unavoidable

energy-width-to-timing jitter is minimized. We estimate an electron timing jitter

(pulse duration) of less than 30fs at a target, possibly down to 10fs, and will

present first experimental results.


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Application of Laser-Triggered Nanometer-Sized Electron Sources in Ultrafast Low-Energy Electron Diffraction and

Ultrafast Transmission Electron Microscopy

Presenter: S. Schäfer (Univ. of Göttingen)

Photoelectron emission from sharp metal tips has received great attention in

recent years. Compared to the widely utilized flat photocathodes, tip-based

photoemitters have potential benefits due to their nanometer-sized emission

area and their large static field-enhancement at the tip apex. Here, we discuss

design considerations for the application of tip-based photoemitters in UTEM and

ULEED. Special emphasis is placed on the quantitative analysis of effective source

dimensions, brightness, coherence and temporal pulse broadening. Numerical

trajectory simulations are compared to experimental results for a laser-triggered

low-energy electron source with picosecond temporal pulse width and a high-

brightness UTEM source.


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Field Emission and Channeling Radiation for High-Spectral-Brilliance X-Ray Sources

Presenter: C. Brau (Vanderbilt University)

For 30-MeV electrons incident on a diamond crystal, channeling X-rays appear

near 56 keV. High spectral brilliance requires a small focal spot at the crystal. The

emittance from a gated field-emitter cathode is 4 nm, which can be focused to a

40-nm spot at 30 MeV. Simulations indicate that emittance growth is small. In

the coming months, we will test the cathodes in an rf gun at Niowave. Next year,

we will begin X-ray experiments using the 4.5-MeV A0 injector at Fermilab,

followed by experiments at the 40-MeV ASTA accelerator.


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Ultrafast Electron Sources Based on Plasmas Produced by Intense Femtosecond Laser Pulses

Presenter: S. Sakabe (Kyoto Univ.)

Using electron pulses accelerated by intense femtosecond laser pulses and

compressed by a static phase rotator, single-shot ultrafast electron diffraction has

been demonstrated. The electron pulses of several hundreds keV are generated

by irradiating tightly focused terawatt femtosecond laser pulses on a polyethylene

foil target, and the pulses are compressed by using an achromatic bending

magnet system. The pulse duration of the electron pulse beam has been

measured by detecting the electrons scattered by intense femtosecond laser

pulses in a direction perpendicular to the electron beam. These femtosecond

electron pulses could have an intensity to take a single-shot diffraction pattern.


35

Toward a High Quality Electron Source from a Laser Wakefield Accelerator for Electron Diffraction

Presenter: J. Faure (LOA)

In this talk, we will review the principles and performances of laser wakefield

accelerators, and focus in particular on their possibility of producing femtosecond

relativistic electron bunches [1]. Femtosecond electron bunches with 100 MeV

energy and few percent energy spread are now commonly produced in laser

wakefield accelerators [2,3]. However, for ultrafast electron diffraction

applications, lower energies in the MeV range are desirable. We will show how

laser wakefield accelerators can be scaled down to MeV energy levels using a

laser system with millijoule energy and kHz repetition rate [4]. Such a source has

intrinsic advantages which could be beneficial to ultrafast electron diffraction:

femtosecond bunch duration, picocoulomb charge and perfect synchronization

(jitter free) with the driving laser pulse. We will also show the results of the first

experiments using a mJ kHz laser system for accelerating electrons. Electrons at

100 keV and kHz repetition rate were produced and used to produce diffraction

patterns on a polycrystalline aluminum thin foil. References [1] O. Lundh et al.,

Nat. Phys. 7 219 (2011) [2] J. Faure et al., Nature 444 737 (2006) [3] C. Rechatin et

al., Phys. Rev. Lett. 102 164801 (2009) [4] A. Lifschitz and V. Malka, NJP 14 053045

(2012)


36

Ultrashort Electron Source from Laser-Plasma Interaction

Presenter: J. Liu (SIOFM, CAS)

By irradiating a flat Al target with femtosecond laser pulses at moderate

intensities of ~1017W/cm2, we obtained stable collimated quasi-monoenergetic

electron beams at ~100 keV close to the specular direction. The periodic

repetition of the electron emission leads to a pulse train of collimated quasi-

monoenergetic electrons with sub-femtosecond duration. The generated quasi-

monoenergetic electron beams with ultrashort duration will find potential

applications in 4D ultrafast time-resolved electron diffraction on a femtosecond

or even attosecond timescale.


37

Concept for Femtosecond Point-Projection Imaging of Nanostructures with Coherent Low-Energy Electron Pulses

Presenter: M. Müller (Fritz-Haber-Institut)

We report on the development of an approach for time-resolved imaging of

nanostructures based on a metal nanotip used as laser-triggered low-energy

electron point source (LEEPS) delivering highly coherent ultrashort electron

pulses. Due to their high sensitivity to electric fields, low-energy electron pulses

are particularly well-suited for mapping transient electric fields and charge

distributions in photoexcited nanostructures. We present first experimental data

on LEEPS projection imaging with femtosecond electron pulses, demonstrating

spatial resolution of several 10 nm. For the upcoming implementation of pump-

probe measurements we expect ~100 femtosecond temporal resolution,

supported by numerical simulations of the electron pulse propagation.


38

m*: A Route to Ultra-bright Photocathodes

Presenter: A. Schroeder (Univ. of Illinois at Chicago)

Robust and low divergence laser-driven pulsed electron sources are the ideal high

brightness sources for ultrafast electron diffraction and microscopy. It is now

evident that the electron effective mass, m*, of the state from which the electron

is emitted plays a key role in determining the transverse emittance, and hence

brightness, of pulsed electron sources. A theoretical formalism, strongly

supported by experimental evidence, will be presented to illustrate the influence

that m* has on electron emission; thereby providing a clear new route towards

laser-driven, ultra-low divergence, planar photocathodes. This work was

supported by DOE NNSA-SSAA grant number DE-FG52-09NA29451.


39

Ultrafast Gas Electron Diffraction

Presenter: M. Centurion (Univ. of Nebraska-Lincoln)

We will present recent results on ultrafast electron diffraction from isolated

molecules, and discuss opportunities and challenges for future gas phase

experiments. We have recently demonstrated 3D imaging of a symmetric top

molecule by using a femtosecond laser to align the molecules, and a femtosecond

electron pulse to capture the diffraction pattern while the molecules are aligned.

The 3D structure of the molecule was retrieved by combining the information

from multiple diffraction patterns corresponding to different projections of the

molecule. This result opens the door to imaging more complex molecules and to

image dynamics on femtosecond time scales.


40

Liquid Jets for Ultrafast Diffraction Experiments

Presenter: U. Weierstall (Arizona State Univ.)

A liquid jet injector has been developed to deliver fully solvated samples into a

probe beam under vacuum conditions. The injector was designed for X-ray

scattering studies of biological nanocrystals and molecules using X-ray Free

Electron Lasers, but is also of interest to ultrafast electron diffraction

experiments. By utilizing a Gas Dynamic Virtual Nozzle (GDVN) to generate a

sample-containing liquid jet of diameter ranging from 300 nm to 20 μm, the

injector avoids the clogging problems with conventional Rayleigh jets. Preliminary

studies using a GDVN for electron diffraction were carried out in the

environmental chamber of a transmission electron microscope.


41

Designing In-situ Experiments in Gas and Liquid Environments for the DTEM

Presenter: P. Abellan (PNNL)

The Dynamic Transmission Electron Microscope (DTEM) at PNNL has been

designed to achieve a combined temporal and spatial resolution of ~10-6s and

~10-10m. This spatio-temporal range covers diverse areas of research in

biochemistry, electrochemistry and catalysis. Critical to all experiments is the

reproducibility of variable conditions around the sample, which may be

maintained using in-situ gas and liquid holders. These environmental holders

allow for localized reactions to be observed with atomic resolution (for pressures

up to 800 Torr in the gas stage). Here, we show our approach to implement in-

situ experiments in gases and liquids inside the DTEM.


42

Time-resolved Gas Electron Diffraction - Building a New Apparatus in Edinburgh

Presenter: D. Wann (Univ. of Edinburgh)

Having worked for many years on time-averaged structures from gas electron

diffraction, the Wann group are now building an apparatus for time-resolved

diffraction. Based on a compact electron gun design, we have started to construct

a new pulsed-source 100 keV set-up, with the first electrons planned for early

2013. Simulations will be presented that predict a resolution of approximately

500 fs in the first instance. Further improvements can be imagined by accounting

for velocity mismatch. Quantum chemical calculations have also been used to

plan the initial experiments that will be performed.


43

Photoelectron Pulse Properties from Free-Free Transitions in Ultrafast Transmission Electron Microscopy

Presenter: D. Flannigan (Univ. of Minnesota)

In this talk, I will describe how ultrafast transmission electron microscopy can be

used to image and control the spatial distribution of femtosecond pulse-

modulated free-free transitions near nanostructures. This is achieved by using an

energy-filter to select a specific electron energy distribution to form the images

while varying the temporal overlap of the photon and photoelectron packets.

Further, I will describe how the properties of the femtosecond photoelectron

packet (distribution and duration) can be measured at the specimen by operating

in the low beam-current regime and quantifying the temporal response of the

low-loss region in the electron-energy spectra.


44

Near Field 4D Electron Microscopy

Presenter: S. T. Park (Caltech)

4D electron microscopy utilizes a pulsed electron packet to image structural

dynamics of nanomaterial, induced by an optical pulse, in real time. In the vicinity

of nanostructures, electrons can directly interact with scattered photons, and

either gain or lose light quanta. This near field photon-electron interaction

enables visualization of nanoscale particles, and is termed photon-induced near

field electron microscopy (PINEM). Here, we give an account of the experimental

results and the theoretical understanding of PINEM, and discuss the impact on

electron microscopy and its applications.


45

Ultrafast Processes on Surfaces Studied by Time-Resolved Reflection High Energy Electron Diffraction

Presenter: T. Frigge (Univ. of Duisburg-Essen)

We study ultrafast processes on surfaces by time-resolved RHEED. In our pump-

probe setup the sample is excited by 50 fs-laser pulses (800 nm). Electron pulses

(7-30 keV) are generated in a Au-photocathode. An incidence angle of 3-6°

ensures surface sensitivity. The velocity mismatch is compensated by tilting the

laser pulse front, which improves the time resolution to 1.8 ps. The transient

temperature is observed through the Debye-Waller effect. Self-organized

nanoscale Ge-clusters were grown on Si(001) in-situ under UHV conditions.

RHEED diffraction patterns allowed the simultaneous investigation of the

transient response of the two different cluster types through spot profile analysis.


46

Determination of Directional Atomic Displacement from Femtosecond Laser Excited Bismuth in Time Resolved

Electron Diffraction

Presenter: P. Zhou (Univ. of Duisburg-Essen)

Time resolved transmission electron diffraction was performed to study the

lattice response of femtosecond laser excited crystalline Bismuth membranes.

The lattice vibration can be driven either indirectly by the relaxation of hot

electrons or directly by the coupling of the laser pulses with the lattice via

nonlinear-optical mechanisms in preferential directions. These different excitation

mechanisms produce distinct signatures in the electron diffraction patterns which

were analyzed by inspection of individual diffraction orders and at different

incidences of the electron beam.


47

Applications of Ultrafast Electron Diffraction

Presenter: C. Y. Ruan (Michigan State Univ.)

The large Ewald sphere and scattering cross-section, and the easiness of forming a

nanoscale focused beam make the electron probes uniquely suited for studying

nanomaterials and complex systems in diffraction and imaging. I will describe

various methods developed and progresses made in the last decade in ultrafast

electron diffraction, which have been applied to study nanoscale materials

transformation and energy transport, plasmonics, and structurally correlated

electronic phase transitions in complex materials. I will also discuss how the

advances of future high-brightness electron microscope can deepen these

investigations and enable imaging of functioning devices with high temporal and

spatial resolutions.


48

A High Repetition Rate-High Brightness Electron Source for Time-Resolved Electron Diffraction and Microscopy

D. Filippetto, F. Sannibale, M. Zolotorev (Lawrence Berkeley National Laboratory)

The advent of RF photo-guns has boosted up the 6D brightness of produced

electron beams by almost two orders of magnitude. The high electric field at the

emission plane enables the creation of sub-picosecond pulses with enough charge

(105-106 electrons) to be used as probe in single-shot time-resolved experiments.

On the other hand, the low repetition rate (10-100 Hz) and the moderate stability

associated with such sources limit the range of applicability to true single-shot

experiments, and the typical time jitter (~ps) poses a lower limit on time

resolution.

The APEX photo-injector is a MHz source of bright beams, merging the high fields

of RF technology with the high repetition rate typical of synchrotron radiation

sources. In will be able to provide electron beams from tents of femtoseconds to

picoseconds beams at MHz repetition rate, with energies up to 750 keV. The high

repetition rate increases the feedback bandwidth, promising time jitters below

well below 100 fs. The electron transport line will be equipped with two

solenoids, an rf buncher, a deflecting cavity and a dispersive region for

longitudinal phase space diagnostic.

Here we report some preliminary considerations in using such source for ultrafast

electron diffraction experiments.


49

Collimated Quasi-monoenergetic Electron Emission at Locked Phases from the Laser-Driven Surface Plasma Wave

Y. Tian (Shanghai Institute of Optics and Fine Mechanics, Chinese Academy of Sciences)

We demonstrate stable collimated quasi-monoenergetic e-beam generation close

to the specular direction by irradiating a flat Al target with femtosecond laser

pulses at moderate intensities. We find that some accelerated electrons more or

less along the specular direction are ejected from the laser-driven surface plasma

wave at locked phases periodically, and inevitably steered slightly toward the

target normal by the ponderomotive force of the combined field of the incident

laser and its coherent reflection. The periodic repetition of the electron emission,

every optical cycle, leads to a pulse train of collimated e-beam with sub-cycle

duration.


50

Complex Acoustic Waves in Graphite Observed by Convergent-Beam Ultrafast Electron Crystallography

W. Liang (Cal Tech)

The second generation of Ultrafast Electron Crystallography (UEC) at Caltech

provides ultrashort electron pulses with tunable probe sizes and convergence

angles. Thereby, a wide area of diffraction experiments becomes feasible.

Employing the convergent-beam mode of UEC, we can investigate

inhomogeneous ultrafast dynamics through Kikuchi diffraction. Intricate laser-

induced acoustic waves in single-crystal graphite were mapped out by the

temporal evolution of Kikuchi patterns. These results demonstrate the unique

ultrafast probe sensitivity of UEC to atomic motions in inhomogeneous systems

and open up new areas for future UEC studies.


51

Continuous MeV electron Diffraction using a Flat Electron Beam

Feichao Fu1,2, Renkai Li3, Xijie Wang4 and Dao Xiang2

1. Department of Physics, Shanghai Jiao Tong University, Shanghai, China 2. SLAC National Accelerator Laboratory, Menlo Park, CA, USA

3. Department of Physics and Astronomy, UCLA, Los Angeles, CA, USA 4. Brookhaven National Laboratory, Upton, NY, USA

In a single-shot continuously time-resolved MeV ultra-fast electron diffraction

system, a thin slit is applied to minimize overlap of diffraction patterns that are

streaked in time by an rf deflecting cavity, which results only part of the

diffraction patterns are recorded at the detector screen.

In this paper, we propose to replace the standard round cathode laser beam

with a flat laser beam with large aspect ratio to obtain sharp recorded

patterns. Given the same area of the laser beam, we convert the simulated

patterns to radial intensity distributions which indicate higher S/N ratio and

better spatial resolution.


52

Controlled Molecules for Time-resolved Electron Diffraction Experiments

N. Mueller (Center for Free-Electron Laser Science, DESY and University of Hamburg)

Controlled molecule imaging increases the amount of information observable

when investigating molecular dynamics by electron diffraction, photoelectron

measurements, or FEL light sources. We prepare gas-phase samples of state-

selected and spatially oriented molecules. The angular distribution of the

molecules is probed by strong-field ionization using velocity map imaging.

Structural information can be gained by ultrafast electron diffraction. A

picosecond electron diffraction setup is under construction and will be combined

with the existing molecular beam setup to investigate complex molecular motions

of the prepared well-defined samples.


53

Design and Implementation of a Flexible Beamline for FS Electron Diffraction Experiments

G. Mancini (LUMES – EPFL)

We discuss the design and implementation of a flexible beamline for femtosecond

electron diffraction experiments in transmission or reflection geometry. By the

use of a radiofrequency compression cavity synchronized to our laser system, in

combination with a set of electron optics, we can control the beam properties in

terms of charge per pulse, transverse spot-size on the sample and temporal

duration of the bunches. The characterization of the beam is performed via a

light-electrons cross-correlation experiment and we demonstrate an overall

temporal resolution around 300 fs for bunches containing up to 105 electrons at a

repetition rate of 20 kHz.


54

Development of High Brightness Electron Source Laboratory at Fermilab

H. Panuganti (Northern Illinois University)

Fermilab is currently commissioning a low energy (4-5 MeV) facility based on an L-

band (1.3 GHz) electron source ― the High Brightness Electron Source Laboratory

(HBESL). The facility is dedicated to R&D on novel cathodes, low energy beam

dynamics, and development of short wavelength radiation sources. HBESL

incorporates a Ti:Sapphire laser system with a sub-fs (6 fs) oscillator as an integral

part of its goal to develop a Tera-watt laser system. In this contribution we will

present the current commissioning of the laser system, and discuss our plans and

preliminary results on our on-going studies (three-photon emission and field

emission).


55

Development of Hybrid Gun for the High Brightness Beam Generation

A. Fukasawa, S. K. Mahapatra, H. To, B. Baumgartner, J. B. Rosenzweig, P. Musumeci, R. Li, UCLA, CA, USA

David Alesini, Luca Ficcadenti, Bruno Spataro, INFN/LNF, Frascati, Italy

A. Valloni, Luigi Palumbo, Rome University La Sapienza, Rome, Italy

We are developing a novel electron beam source, so called ‘hybrid gun’. It has

both standing wave (SW) and traveling wave (TW) cells in one RF structure.

The SW part works as an RF gun, and the TW part is used to add energy

modulation in the longitudinal direction, so that the beam is compressed by

ballistic bunching. A PARMELA simulation showed it is possible to generate the

beam with the charge 10 pC, energy 3 MeV, the rms bunch length 70 fs, and

the normalized emittance 0.3 mm.mrad. We have made the structure and

commissioned it up to 10 MW successfully, although the design input power is

25 MW. The generation of the beam is expected in January, 2013.


56

Dispersion Compensation for Attosecond Electron Pulses

M. Centurion (University of Nebraska – Lincoln)

We propose a device to compensate for the dispersion of attosecond electron

pulses. The device uses only static electric and magnetic fields and therefore does

not require synchronization to the pulsed electron source. Analogous to the well-

known optical dispersion compensator, an Electron Dispersion Compensator

separates paths by energy in space. Magnetic fields are used as the dispersing

element, while a Wien filter is used for compensation of the electron arrival

times. We analyze a device with a size of centimeters, which can be applied to

ultrafast electron diffraction and microscopy, and fundamental studies.


57

High Brightness Sub-picosecond Electron Pulse Generation

J. Li (East China Normal University, State Key Laboratory of Precision Spectroscopy)

Femtosecond electron gun determines the temporal resolution of UED system.

The pulse duration of high-brightness electron bunch will be broadened because

of the space charge effect which results in the loss of temporal resolution. In our

setup, a DC acceleration and RF compression technology is applied to generate

sub-picosecond electron pulses with ≥ 105 electrons. The electrons are firstly

accelerated by a 10MV/m DC electric field, and then pass through a 3.2GHz RF

compression cavity with TM010 mode phase-locked to femtosecond laser

oscillator. The electron bunch acquires a chirp inversely to SC expansion, and so it

will be compressed.


58

Multi-Objective Molecular Dynamics Simulations with the GPT Code

B. van der Geer (Pulsar Physics)

In the high-brightness community we typically want it all: Lots of charge, low

emittance and short pulse-duration. During the design process it is common to

take space-charge forces into account, but at higher brightness stochastic effects

play an increasingly important role. Furthermore we need to include higher order

lens aberrations and external constraints. Advances in computational speed and

numerical algorithms allow us to run multi-objective optimizations with the GPT

code, taking into account all relevant physics affecting bunch quality at the

sample. This automatically shows trade-offs between conflicting objectives in

addition to providing the global optimum for the entire system.


59

Time Resolved Electron Diffraction on Nanomaterials

P. Zhou (Faculty of Physics, University of Duisburg-Essen)

Experimental investigations of different nanomaterials with time-resolved

electron diffraction are reported. The experiments were performed either in

reflection (GaAs nanowires) or in transmission (gold nanoparticles) geometry. In

reflection geometry space charge effects have a substantial influence on the

observed changes in the diffraction signals. Nevertheless, it is still possible to gain

information about the lattice response by analyzing the diffraction orders

individually. In contrast, transmission diffraction is less effected by space charge

so that ultrafast lattice heating can be readily observed. The results demonstrate

the possibilities and limitations of time resolved electron diffraction on

nanomaterials.


60

Ultracold and Ultrafast Electrons Diffracted from Graphene

E. Vredenbregt (Eindhoven University of Technology)

We develop a new class of electron source using pulsed photoionization of

trapped atoms to create intense electron pulses with large coherence length.

Temperatures of a few Kelvin are achieved for tens of thousands electrons. We

now report on picosecond pulses using ultrafast lasers for the ionization step. Low

temperatures can still be achieved despite the photon energy spread. We explain

this surprising result from electron trajectories resulting from photoionization,

and show how polarization effects can be understood. Diffraction from graphene

is used to characterize the coherence of the beam. Characterization of the bunch

length using a streak cavity follows.


61

Ultrafast Time Resolved Surface Sensitive Electron Diffraction with Tilted Pump Pulse Fronts

C. Streubühr (Faculty of Physics, University of Duisburg-Essen)

Time resolved reflection high energy electron diffraction (TR-RHEED) is a surface

sensitive technique to investigate the lattice dynamics of surfaces. The different

velocities of light and electrons result in a time mismatch between the laser

excitation and electron probe pulse (velocity mismatch). As a consequence the

temporal resolution is limited. In this contribution we report the use of an optical

setup capable of matching the pulse front of the laser to the electron pulse. The

improvement of the temporal resolution is demonstrated by measuring the

ultrafast lattice heating of Pb islands on a Si(111) surface.

workshop on ultrafast electron sources for diffraction and ...pbpl.physics.ucla.edu/uesdm_2012/uesdm...

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