Workshop on Frontiers in Ultrafast Scattering of Electrons

Aug 27, 2025, 8:00 AM → Aug 29, 2025, 5:00 PM America/Los_Angeles

48/1-112A/B/C/D - Redwood Rooms (SLAC)

Alexander Reid (SLAC), Joel England (SLAC)

We are pleased to announce the first workshop on Frontiers in Ultrafast Scattering of Electrons (FUSE), to be held August 27-29, 2025 at SLAC National Accelerator Laboratory in Menlo Park, California. The workshop aims to enhance the visibility of relativistic electron scattering as a critical research tool, foster collaboration across the broader ultrafast electron diffraction (UED) community (including both relativistic and nonrelativistic UED instruments), and serve as a platform for practitioners to exchange ideas, share breakthroughs, and address emerging challenges. The workshop is open to the global UED science and instrument development community to attend. We will arrange invited talks from international leaders, particularly those from regions with significant UED investments, to relate recent scientific developments, share capabilities and progress from emerging UED facilities, and identify opportunities for innovation. An auxilliary goal is to inform SLAC’s MeV-UED program so that it will remain user-driven while adapting to evolving trends in ultrafast science. Such engagement will be vital for maintaining the value of MeV-UED as a research tool and maximizing its scientific impact. 

Wed, August 27

8:00 AM → 8:30 AM Coffee Break

8:30 AM → 9:30 AM Welcoming Remarks

Convener: Joel England (SLAC)

8:30 AM Welcoming Remarks

Speaker: Mike Dunne (SLAC)

8:40 AM Historical Perspective on MeV Electron Microscopy and Diffraction and Progress in the Field

Speaker: Yimei Zhu (BNL)

9:10 AM Logistics and Workshop Charge

Speaker: Joel England (SLAC)

9:30 AM → 10:00 AM Coffee Break

10:00 AM → 12:30 PM UED Facilities

Convener: Stephen Weathersby (SLAC)

10:00 AM 3D atomic structure determination with MeV electron diffraction

Speaker: Alke Meents

10:30 AM The Future RUEDI (The Relativistic Ultrafast Electron Diffraction and Imaging) UK facility

Speaker: Julian McKenzie

12:30 PM → 2:00 PM Lunch

2:00 PM → 5:15 PM MeV-UED Enabled Ultrafast Chemical Science in Gas and Liquid Phases

Gas and Liquid Phase Chemical Science Enabled by MeV-UED

Convener: Yusong Liu (SLAC)

2:00 PM Speaker Introductions and Session Overview

Provide an introduction to the invited speakers and an overview of the scientific presentations in the session.

Speaker: Dr Yusong Liu (SLAC, LCLS)

2:05 PM Gas-phase Ultrafast Electron Diffraction: Achievements, challenges and opportunities

Gas-phase ultrafast electron diffraction (UED) has become a powerful tool for capturing molecular dynamics with femtosecond temporal and atomic spatial resolutions, enabling direct observation of phenomena such as photo-dissociation, ring-opening reactions, and nuclear wavepacket motion through conical intersections. Despite significant progress, several challenges remain: temporal resolution is limited by space-charge-induced pulse broadening; background signal subtraction is complex; structural retrieval methods lack standardization and are error-prone in low-signal regimes; and stable delivery of gas-phase samples with sufficient density is technically demanding. Advances in relativistic electron sources, pulse compression, electron counting detectors, and novel data analysis methods are rapidly expanding the capabilities of gas-phase UED, enabling studies of increasingly complex systems. This talk will provide an overview of the current capabilities, highlight persistent technical challenges, and explore future directions for UED within the broader context of ultrafast science.

Speaker: Dr Pedro Nunes (Diamond Light Source, Ltd)

2:35 PM Studying the UV-induced isomerization and dissociation dynamics of gas-phase oxazole and isoxazole

The five-member ring isomers oxazole and isoxazole (C3H3NO) are an interesting model system for studying UV-induced isomerization and dissociation since the different types of bonds in both isomers (C-N-C-O vs C-N-O-C) are predicted to lead to very different reaction products and dynamics. I will present time-resolved product yields for both isomers obtained from a recent GUED experiment and compare the experimental findings to results of trajectory surface hopping simulations as well as time-resolved Coulomb explosion imaging experiments performed at Kansas State University.

Speaker: Prof. Daniel Rolles (Kansas State University)

3:05 PM UED Studies of the UV Photochemistry of Isolated and Solvated Bromoform

Bromoform (CHBr3) is a natural compound whose UV photodissociation products contribute to ozone depletion in the Earth’s atmosphere. Ultrafast electron diffraction is used to study atomic rearrangements in isolated and in solvated bromoform molecules after 267 nm excitation. The gas phase study provides the first experimental visualization of a long-predicted ultrafast isomerization channel. The rate-of-formation, lifetime, and predominant yield, relative to a previously observed direct dissociation channel, challenge state-of-the-art theories (JACS 2024, 146, 28070, DOI: 10.1021/jacs.4c07165). More recently, a liquid phase UED study has been performed on bromoform solvated in 1-propanol to test and refine previously reported, solvent-mediated UV reaction mechanisms. Parallels and differences between the observed gas- and solution-phase dynamics will be discussed.

Speaker: Dr Oliver Gessner (LBNL)

3:35 PM Coffee Break

3:40 PM Capturing Chemical Motion in Solution: Insights from Femtosecond X-ray and Electron Scattering

Femtosecond X-ray solution scattering (XSS) has enabled us to capture photoinduced structural dynamics in solvated transition metal complexes with atomic-scale resolution, revealing intramolecular changes, vibrational coherences, and solvation dynamics. In this talk, I will present recent XSS results from the LCLS, with a particular emphasis on tracking photoinduced solute–solvent hydrogen-bond rearrangements coupled to ultrafast electron transfer (Nature Chem. 13, 343–349, 2021). I will also discuss opportunities for probing chemical dynamics in solution using ultrafast electron diffraction (UED), highlighting insights from the photodissociation of tri-iodide studied at the LCLS MeV-UED instrument (Struct. Dyn. 7, 064901, 2020).

Speaker: Dr Elisa Biasin

4:10 PM Laser-Induced Streaking in Liquid-Phase Ultrafast Electron Diffraction

Laser-induced streaking (LIS) of electron beam, first observed by Zewail group back in 1994, is a unique phenomenon in UED that is often used to conveniently identify time-zero in UED experiments. In the gas phase, LIS originates from plasma field created by strong field ionization of sample molecules, hence named as “photoionization-induced lensing” by Zewail. Separately, LIS can also be achieved with THz pulses, known as the THz streaking. THz streaking do not involve photoionization, but originates from the amplification of the electric field of THz pulses by a metal cavity. In this presentation, I will show our preliminary results on LIS in liquid-phase UED. We found that in liquid-phase, LIS can originate from a third mechanism that is different from the two mechanisms above. In addition to the main beam, liquid-phase LIS also streaks the diffraction pattern. This phenomenon creates both complexity and new opportunity for future liquid-phase UED experiments.

Speaker: Prof. Jie Yang (TsingHua University)

Thu, August 28

8:00 AM → 8:30 AM Coffee Break

8:30 AM → 10:30 AM Solid State & Quantum Materials

Convener: Alexander Reid (SLAC)

10:00 AM Attosecond quantum electron imaging for different applications in science

Speaker: Prof. Mohammed Hassan (University of Arizona)

10:30 AM → 11:00 AM Coffee Break

11:00 AM → 1:00 PM Electron Sources & Beam Optics

Convener: Fuhao Ji (SLAC)

11:00 AM Pushing the limits of Ultrafast Electron Diffraction and Imaging at Tsinghua University

Speaker: Renkai Li (Tsinghua University)

11:30 AM Novel Cathodes for Dark Current Mitigation in LCLS-II Injector Gun

High rep-rate SRF-Linac based XFEL like LCLS-II has a stringent requirement on the limit of the dark current from the injector RF gun. In this talk, we will present our recent work on mitigating the LCLS-II gun dark current by re-designing the photo cathode.  New cathode plugs with ~1mm insertion have been designed, manufactured and commissioned at LCLS-II. They successfully reduce the gun dark from ~uA to ~nA level, and can potentially enable further improvement on the beam emittance.

Speaker: Tianhuan Luo (Lawrence Berkeley National Laboratory)

12:00 PM C-band high-gradient photoinjector R&D at LANL CARIE facility

Two high-gradient 1.6-cell normal-conducting RF photoinjectors at C-band were designed for operation at the Cathodes And Radiofrequency Interaction in Extremes (CARIE) facility at Los Alamos National Laboratory (LANL). The first photoinjector cavity uses a planar copper cathode and has been fabricated and tuned at low power. The second photoinjector cavity was designed for using INFN-style photocathode inserts and is currently under fabrication. The high-power RF system of CARIE comprising a 50-MW 5.712-GHz klystron, circulator, and waveguide line has been conditioned to providing 12 MW with 1-µs pulse length.

Speaker: Haoran Xu (Los Alamos National Laboratory)

12:30 PM Design of the RUEDI ultrafast electron diffraction beamline at Daresbury Laboratory

RUEDI (Relativistic Ultrafast Diffraction and Imaging) is a planned UK national user facility. It has a diffraction beamline optimised for temporal resolution. This beamline uses an S-band normal conducting RF gun followed by a triple bend achromat magnetic compressor which simultaneously compresses the bunch and suppresses the time of arrival jitter to the 10 fs scale. The compressor has variable R56, sextupoles for control of T566 and optics designed to mitigate space charge degradation of the electron beam quality. After the sample the diffraction patterns are magnified onto the detector using flexible variable camera length solenoid optics.

Speaker: Ben Hounsell (STFC UKRI)

1:00 PM → 2:30 PM Lunch

2:30 PM → 4:30 PM Supporting Technologies & Diagnostics

Convener: Cameron Duncan (SLAC)

4:30 PM → 6:30 PM Poster Session

6:30 PM → 8:30 PM Dinner

Fri, August 29

8:00 AM → 8:30 AM Coffee Break

8:30 AM → 10:00 AM Materials at Extreme Conditions

Convener: Mianzhen Mo (SLAC)

8:30 AM Ultrafast Structural Evolution of Warm Dense Matter

Speaker: Prof. Benjamin Ofori-Okai (SLAC)

9:00 AM Radiation induced damage in nuclear materials studied with UED and modeling

Experimental study of early damage in nuclear damage has been very challenging due to low quantity and small size of defects. Therefore, being able to reliably validate modelling techniques of primary damage in nuclear materials has not been possible. Recent, advances in UED experiments has made it possible to study the dynamics of the material due to laser excitation. By comparing the signals from damaged and undamaged material it could be possible to evaluate the types of defects and their concentrations experimentally. Moreover, UED experiments can be directly simulated with computer modelling and, therefore makes it possible to validate the models being used.

In this presentation we present the combined experimental and modelling study to assess the damage and its role on the materials response to laser excitation of pristine and He implanted sample.

Speaker: Prof. Artur Tamm (University of Tartu)

9:30 AM Ultrafast electron-diffraction studies of materials under extreme conditions

Speaker: Dr Mianzhen Mo (SLAC)

10:00 AM → 10:30 AM Coffee Break

10:30 AM → 12:00 PM Cross-Cutting UED Science

In this session, we will focus on the applications of using UED, XUV and similar techniques on the in-situ/operando spectroscopy

Convener: Ming-Fu Lin (SLAC)

10:30 AM Probing in-operando device dynamics and atomic-scale energy flows with UED

Speaker: Prof. Aditya Sood (Princeton University)

11:00 AM Imaging photoexcited carriers and heat transport in nanoscale materials using ultrafast EELS

Speaker: Prof. Scott Cushing (Caltech)

12:00 PM → 12:30 PM Workshop Closeout

12:30 PM → 2:00 PM Lunch