A5089547326- Particle Accelerators and Free-Electron Lasers
- Particle accelerators and beam dynamics
- Advanced X-ray Imaging Techniques
- Laser-Plasma Interactions and Diagnostics
- Magnetic confinement fusion research
- Gyrotron and Vacuum Electronics Research
- Particle Detector Development and Performance
- Superconducting Materials and Applications
- Advanced Optical Sensing Technologies
- X-ray Spectroscopy and Fluorescence Analysis
- Electron and X-Ray Spectroscopy Techniques
- Photocathodes and Microchannel Plates
- Plasma Diagnostics and Applications
- Laser-Matter Interactions and Applications
- Advanced Electron Microscopy Techniques and Applications
- Advanced Chemical Physics Studies
- Adaptive optics and wavefront sensing
- Advancements in Photolithography Techniques
- Calibration and Measurement Techniques
- Ocular and Laser Science Research
- Laser Design and Applications
- Semiconductor materials and devices
- Nuclear Physics and Applications
- Optical Systems and Laser Technology
- Thermal properties of materials
SLAC National Accelerator Laboratory
2012-2023
Menlo School
2004-2023
Stanford Synchrotron Radiation Lightsource
1995-2021
Stanford University
1995-2017
Linac Coherent Light Source
2007-2016
University of Illinois Urbana-Champaign
2014
University of Michigan–Ann Arbor
2014
NOAA Chemical Sciences Laboratory
2004
Office of Basic Energy Sciences
1999
Office of Science
1999
The recently discovered phenomenon of broadband white-light emission at room temperature in the (110) two-dimensional organic–inorganic perovskite (N-MEDA)[PbBr4] (N-MEDA = N1-methylethane-1,2-diammonium) is promising for applications solid-state lighting. However, spectral broadening mechanism and, particular, processes and dynamics associated with emissive species are still unclear. Herein, we apply a suite ultrafast spectroscopic probes to measure primary events directly following...
Ultrafast electron probes are powerful tools, complementary to x-ray free-electron lasers, used study structural dynamics in material, chemical, and biological sciences. High brightness, relativistic beams with femtosecond pulse duration can resolve details of the dynamic processes on atomic time length scales. SLAC National Accelerator Laboratory recently launched Electron Diffraction (UED) microscopy Initiative aiming at developing next generation ultrafast scattering instruments. As first...
Observing the motion of nuclear wavepackets during a molecular reaction, in both space and time, is crucial for understanding controlling outcome photoinduced chemical reactions. We have imaged vibrational wavepacket isolated iodine molecules using ultrafast electron diffraction with relativistic electrons. The time-varying interatomic distance was measured precision 0.07 {\AA} temporal resolution 230 fs full-width at half-maximum (FWHM). method not only sensitive to position but also shape...
Abstract Imaging changes in molecular geometries on their natural femtosecond timescale with sub-Angström spatial precision is one of the critical challenges chemical sciences, as nuclear geometry determine reactivity. For photoexcited molecules, dynamics photoenergy conversion path and efficiency. Here we report a gas-phase electron diffraction experiment using megaelectronvolt (MeV) electrons, where captured rotational wavepacket nonadiabatically laser-aligned nitrogen molecules. We...
Li-rich layered materials are important cathode compounds used in commercial lithium ion batteries, which, however, suffers from some drawbacks including the so-called voltage fade upon electrochemical cycling. This study employs novel transmission X-ray microscopy to investigate reaction induced morphological and chemical changes Li2Ru0.5Mn0.5O3 particles at meso nano scale. Combined spectroscopy, diffraction experiments performed systematically this material's evolution cycling as well...
Electron–phonon coupling processes determine electronic transport properties of materials and are responsible for the transfer excess energy to lattice. With decreasing device dimensions an understanding these in nanoscale is becoming increasingly important. Here we use time-resolved electron diffraction directly study relaxation thin bismuth films after optical excitation. Precise measurements transient Debye–Waller-effect various film thicknesses over extended range excitation fluences...
We present results on ultrafast gas electron diffraction (UGED) experiments with femtosecond resolution using the MeV gun at SLAC National Accelerator Laboratory. UGED is a promising method to investigate molecular dynamics in phase because pulses can probe structure high spatial resolution. Until recently, however, it was not possible for reach relevant timescale motion of nuclei during reaction. Using has allowed us overcome main challenges reaching resolution, namely delivering short...
We report measurements of the transient structural response weakly photo-excited thin films BiFeO3, Pb(Zr,Ti)O3, and Bi time-scales for interfacial thermal transport. Utilizing picosecond x-ray diffraction at a 1.28 MHz repetition rate with time resolution extending down to 15 ps, changes in angle are recorded. These associated photo-induced lattice strains within nanolayer films, resolved part-per-million level, corresponding shift scattering three orders magnitude smaller than rocking...
Abstract Understanding the fundamentals of nanoscale heat propagation is crucial for next‐generation electronics. For instance, weak van der Waals bonds layered materials are known to limit their thermal boundary conductance (TBC), presenting a dissipation bottleneck. Here, new nondestructive method presented probe transport in crystalline using time‐resolved X‐ray measurements photoinduced strain. This technique directly monitors time‐dependent temperature changes crystal and subsequent...
Abstract Currently, our general approach to retrieving molecular structures from ultrafast gas-phase diffraction heavily relies on complex ab initio electronic or vibrational excited state simulations make conclusive interpretations. Without such simulations, inverting this measurement for the structural probability distribution is typically intractable. This creates a so-called inverse problem. Here we address problem by developing broadly applicable method that approximates frame structure...
We present a dedicated end-station for solution phase high repetition rate (MHz) picosecond hard x-ray spectroscopy at beamline 15-2 of the Stanford Synchrotron Radiation Lightsource. A high-power ultrafast ytterbium-doped fiber laser is used to photoexcite samples 640 kHz, while data acquisition operates 1.28 MHz storage ring recording in an alternating on-off mode. The time-resolved measurements are enabled via gating detectors with 20 mA/70 ps camshaft bunch SPEAR3, mode available during...
This paper reviews an efficient implementation of the software 'middle layer' that resides between high-level accelerator control applications and low-level system. The middle layer is written in MATLAB includes links to EPICS Channel Access Library. Functionally, syntax closely parallels Family/Index naming scheme used many simulation codes uses same convention communicate with both online machine model. Hence, control, data analysis tools are integrated into a single, easy-to-use package.
Matlab is an interpretive programming language originally developed for convenient use with the LINPACK and EISPACK libraries. appealing accelerator physics because it matrix-oriented, provides active workspace system variables, powerful graphics capabilities, built-in math libraries, platform independence. A number of software toolboxes have been written in - Accelerator Toolbox (AT) model-based machine simulations, LOCO on-line model calibration, Channel Access (MCA) to connect EPICS. The...
In the interest of obtaining shorter bunch length for X-ray pulses, we have developed a low-alpha operational mode SPEAR3. this momentum compaction factor is reduced by 21 or more from usual achromat introducing negative dispersion at straight sections. We successfully stored 100 mA with normal fill pattern lifetime 30 hrs. The was measured to be 6.9 ps, compared 17 ps in mode. paper report our studies on lattice design and calibration, orbit stability, higher order alpha measurement,...
This paper presents measurements and analysis of the quantum efficiency (QE) intrinsic emittance Cu CsBr coated photocathodes. The data uses expressions for metal cathodes previously derived from Spicer's three-step model photoemission. Data taken with a 257 nm CW laser on (100) crystals indicate an 0.77 (μm/mm-rms) 0.42 uncoated cathodes. high low observed have applications in free electron other devices requiring brightness beams.
A weak vertical coupled-bunch instability with oscillation amplitude of the order a few $\ensuremath{\mu}\mathrm{m}$ has been observed in SPEAR3 at nominal vacuum pressure. The becomes stronger increasing neutral gas pressure as by turning off pumps, and weaker when beam emittance is increased. These observations indicate that motion driven ions trapped periodic potential electron beam. In this paper we present series comprehensive measurements, impedance-based stability analysis, numerical...
A series of bunch length measurements were made in SPEAR3 for two different machine optics. In the achromatic optics increases from low-current value 16.6 ps rms to about 30 at 25 ma/bunch yielding an inductive impedance -0.17 Omega. Reducing momentum compaction factor by a ~60 [1] yields ~4 rms. this paper we review experimental setup and results.
CsBr photocathodes have 10 times higher quantum efficiency with only 3 larger intrinsic transverse emittance than copper. They are robust and can withstand $80\text{ }\text{ }\mathrm{MV}/\mathrm{m}$ fields without breaking down or emitting dark current. operate in $2\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}9}\text{ }\mathrm{torr}$ vacuum survive exposure to air. well suited for generating high pulse charge rf guns a photocathode transfer system.