A5035533418- Advanced X-ray Imaging Techniques
- Crystallography and Radiation Phenomena
- X-ray Spectroscopy and Fluorescence Analysis
- Particle Accelerators and Free-Electron Lasers
- High-pressure geophysics and materials
- Advanced Electron Microscopy Techniques and Applications
- Laser-Plasma Interactions and Diagnostics
- Diamond and Carbon-based Materials Research
- X-ray Diffraction in Crystallography
- Medical Imaging Techniques and Applications
- Magnetic properties of thin films
- Atomic and Molecular Physics
- Enzyme Structure and Function
- Electron and X-Ray Spectroscopy Techniques
- Ion-surface interactions and analysis
- Laser-Matter Interactions and Applications
- Advanced X-ray and CT Imaging
- Particle accelerators and beam dynamics
- Photorefractive and Nonlinear Optics
- Advanced Fiber Laser Technologies
- Rare-earth and actinide compounds
- Nuclear Physics and Applications
- Nuclear materials and radiation effects
- Material Dynamics and Properties
- Iron oxide chemistry and applications
Washington State University
2025
University of South Alabama
2023-2024
SLAC National Accelerator Laboratory
2013-2023
Menlo School
2003-2021
Linac Coherent Light Source
2011-2021
University of California, Berkeley
2008-2016
University of Michigan–Ann Arbor
2007-2016
Deutsches Elektronen-Synchrotron DESY
2016
Los Alamos National Laboratory
2016
Czech Academy of Sciences, Institute of Physics
2016
Intense femtosecond laser excitation can produce transient states of matter that would otherwise be inaccessible to laboratory investigation. At high densities, the interatomic forces bind solids and determine many their properties substantially altered. Here, we present detailed mapping carrier densityâdependent potential bismuth approaching a solid-solid phase transition. Our experiments combine stroboscopic techniques use high-brightness linear electron acceleratorâbased x-ray source...
Intense femtosecond x-ray pulses from free-electron laser sources allow the imaging of individual particles in a single shot. Early experiments at Linac Coherent Light Source (LCLS) have led to rapid progress field and, so far, coherent diffractive images been recorded biological specimens, aerosols, and quantum systems with few-tens-of-nanometers resolution. In March 2014, LCLS held workshop discuss scientific technical challenges for reaching ultimate goal atomic resolution single-shot...
Linear-accelerator-based sources will revolutionize ultrafast x-ray science due to their unprecedented brightness and short pulse duration. However, time-resolved studies at the resolution of duration are hampered by inability precisely synchronize an external laser accelerator. At Sub-Picosecond Pulse Source Stanford Linear-Accelerator Center we solved this problem measuring arrival time each high energy electron bunch with electro-optic sampling. This measurement indirectly determined...
Delayed coherent nuclear forward scattering of synchrotron radiation by polycrystalline Fe foils (both isotopically enriched and naturally abundant) has been measured. Quantum beats wre observed in the time spectra. With chosen experimental conditions these can only arise from scattering. The 5-meV bandwidth provided a special silicon crystal monochromator obviates need for resonant filter. This direct approach offers possibility performing wide range M\"ossbauer spectroscopy experiments...
Specular reflectivity of p-polarized light near the iron ${\mathit{L}}_{\mathrm{II}}$ and ${\mathit{L}}_{\mathrm{III}}$ absorption edges was measured from a single-crystal film with an external magnetic field perpendicular to scattering plane. Large changes in were observed upon reversal direction field. We attribute this resonant magnetization-sensitive effect interference between nonmagnetic contribution scattering. Similar effects can be expected other ferromagnetic ferrimagnetic systems.
X-ray free-electron lasers (FELs) produce femtosecond x-ray pulses with unprecedented intensities that are uniquely suited for studying many phenomena in atomic, molecular, and optical (AMO) physics. A compilation of the current developments at Linac Coherent Light Source (LCLS) future plans LCLS-II Next Generation (NGLS) outlined. The AMO instrumentation LCLS its performance parameters summarized. few selected experiments representing rapidly developing field ultra-fast peak intensity...
We have developed different types of photodetectors that are based on the photoionization a gas at low target density. The almost transparent devices were optimized and tested for online photon diagnostics current future x-ray free-electron laser facilities shot-to-shot basis with temporal resolution better than 100 ns. Characterization calibration measurements performed in laboratory Physikalisch-Technische Bundesanstalt electron storage ring BESSY II Berlin. As result, measurement...
The Linac Coherent Light Source has added a self-seeding capability to the soft x-ray range using grating monochromator system. We report demonstration of with measured resolving power 2000--5000, wavelength stability ${10}^{\ensuremath{-}4}$, and an increase in peak brightness by factor 2--5 across photon energy 500--1000 eV. By avoiding need for at experimental station, self-seeded beam can deliver as much 50-fold higher users.
We present the first highly resolved measurements of plasmon spectrum in an ultrafast heated solid. Multi-keV x-ray photons from Linac Coherent Light Source have been focused to one micrometer diameter focal spots producing solid density aluminum plasmas with a known electron n_{e}=1.8×10^{23} cm^{-3}. Detailed balance is observed through intensity ratio up- and down-shifted plasmons forward scattering spectra measuring temperature. The damping treated by electron-ion collision models beyond...
We report clear experimental evidence for second harmonic generation at hard x-ray wavelengths. Using a 1.7 Å pumping beam generated by free electron laser, we observe in diamond. The is of order 10 times the background radiation, scales quadratically with pump pulse energy, and over narrow phase-matching condition. Of importance future experiments, our results indicate that it possible to nonlinear processes crystals intensities exceeding 1016 W/cm2.
The existence of charge density wave (CDW) correlations in cuprate superconductors has now been established. However, the nature ground state order remained uncertain because disorder and presence superconductivity typically limit CDW correlation lengths to a dozen unit cells or less. Here we explore YBa2Cu3Ox (YBCO) ortho-II ortho-VIII crystals, which belong cleanest available family, at magnetic fields excess resistive upper critical field (Hc2) where is heavily suppressed. We find an...
In a free-electron laser (FEL) the lasing medium is high-energy beam of electrons flying with relativistic speed through periodic magnetic field. The interaction between synchrotron radiation that produced and in induces bunching electrons, greatly increasing intensity at particular wavelength. Depending only on phase match electron energy period, wavelength FEL can be continuously tuned within wide spectral range. concept adapted to produce wavelengths from millimetres Ångstroms, principle...
We present experimental evidence for achieving significant x-ray flux enhancement by coupling a highly collimated and monochromatic synchrotron beam into Si/polyimide/${\mathrm{SiO}}_{2}$ thin-film waveguide. The observed 20-fold increase agrees with theoretical predictions was limited only absorption of the 1 \AA{} x rays in waveguide structure.
Dichroic interference effects were observed in circularly polarized soft-x-ray reflectivity at the Co ${\mathit{L}}_{2,3}$ edges of a magnetic multilayer. The data show maximum asymmetry ratio 80%, greater than degree circular polarization incident light, changeover dichroic characteristics with increasing grazing angle, and an inverted pattern angular dependence ratio. These observations are explained successfully by classical electromagnetic model calculation which includes complete state...
A method to measure spin-dependent x-ray-absorption spectra that does not require long-range magnetic order is presented. It based on the spin dependence of emission spectrum. Using a high-resolution spectrometer separate and select different spin-polarized final states in K\ensuremath{\beta} fluorescence spectrum MnO ${\mathrm{MnF}}_{2}$, absorption vicinity Mn K edge were measured. Since this uses direction local moment as reference it can be applied paramagnetic antiferromagnetic systems...
We experimentally and theoretically study the coincidence count rate for down-converted x-ray photons. Because of photoionization, parametric down-conversion at wavelengths generally involves loss theoretical description requires a Langevin approach. By working in transmission geometry (Laue) rather than Bragg previous experiments, we obtain an improvement signal-to-noise ratio 12.5, find agreement between experiment theory.
We describe a gas-phase x-ray scattering experiment capable of capturing molecular motions with atomic spatial resolution and femtosecond time resolution. X-ray free electron lasers can deliver intense pulses ultrashort duration, making them suitable to study ultrafast chemical reaction dynamics in an ultraviolet pump, probe scheme. A cell diffractometer balances sample flow gas density laser focusing conditions provide adequate vector high signal intensity near-uniform excitation...
In the field of beam physics, two frontier topics have taken center stage due to their potential enable new approaches discovery in a wide swath science. These areas are: advanced, high gradient acceleration techniques, and x-ray free electron lasers (XFELs). Further, there is intense interest marriage these fields, with goal producing very compact XFEL. this context, recent advances radio-frequency cryogenic copper structure research opened door use surface electric fields between 250 500...
Water adsorption isotherms from 25 to 125 °C were measured for three metal–organic frameworks (MOFs), MOF-303, MOF-LA2-1, and MIL-100(Fe), which are frequently studied water harvesting applications. The results show how the step in isotherm varies as a function of temperature detail combination pressure necessary remove adsorbed water. Furthermore, isobaric–isothermal Gibbs ensemble Monte Carlo simulations performed MOF-303 shed light on change occupation numbers different known sites with...
The weak ${2p}^{5}{4f}^{n+1}$ quadrupolar excitation is separated from the intense ${2p}^{5}{5d}^{1}$ white line at gadolinium ${L}_{\mathrm{III}}$ absorption edge in ${\mathrm{Gd}}_{3}{\mathrm{Ga}}_{5}{O}_{12}$ by resonant inelastic x-ray scattering. This separation obtained monitoring intensity of ${3d}^{9}{4f}^{n+1}{5d}^{0}$ and ${3d}^{9}{4f}^{n}{5d}^{1}$ multiplet families, which are resonantly enhanced intermediate energies, respectively. dipolar excitations detected spite Gd $2p$...
Nuclear Bragg scattering of synchrotron radiation from isotopically enriched $^{57}\mathrm{Fe}_{2}$${\mathrm{O}}_{3}$ has been observed at a signal-to-noise ratio 100:1 without delayed-coincidence techniques. The use high-resolution premonochromator providing 5-meV energy spread and 0.4'' collimation allows for studies dynamical diffraction effects. In particular, the intensity pure nuclear (7,7,7) reflection implies dramatic decrease effective lifetime due to coherent scattering.