A5043991853- Particle Accelerators and Free-Electron Lasers
- Advanced X-ray Imaging Techniques
- Particle accelerators and beam dynamics
- Crystallography and Radiation Phenomena
- Advanced Electron Microscopy Techniques and Applications
- Photocathodes and Microchannel Plates
- Gyrotron and Vacuum Electronics Research
- Atomic and Subatomic Physics Research
- Laser-Plasma Interactions and Diagnostics
- Superconducting Materials and Applications
- Laser Design and Applications
- Particle Detector Development and Performance
- Electron and X-Ray Spectroscopy Techniques
- Laser-Matter Interactions and Applications
- Radiation Detection and Scintillator Technologies
- X-ray Spectroscopy and Fluorescence Analysis
- Nonlinear Photonic Systems
- Cold Atom Physics and Bose-Einstein Condensates
- Plasma Diagnostics and Applications
- High-pressure geophysics and materials
- Diamond and Carbon-based Materials Research
- Medical Imaging Techniques and Applications
- Advanced Surface Polishing Techniques
- Engineering Structural Analysis Methods
- Advanced X-ray and CT Imaging
SLAC National Accelerator Laboratory
2018-2025
Stanford University
2020-2023
Brigham Young University
2023
Menlo School
2020-2022
University of Chicago
2020-2021
Northern Illinois University
2015-2019
Fermi National Accelerator Laboratory
2016-2019
University of California, Los Angeles
2018-2019
St Petersburg University
2018
Belarusian State University
2012-2017
Abstract Objectives This study examined public discourse and sentiment regarding older adults COVID-19 on social media assessed the extent of ageism in discourse. Methods Twitter data (N = 82,893) related to both dated from January 23 May 20, 2020, were analyzed. We used a combination science methods (including supervised machine learning, topic modeling, analysis), qualitative thematic analysis, conventional statistics. Results The most common category coded tweets was “personal opinions”...
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...
An approach to modeling the dynamics of x-ray amplified spontaneous emission and superfluorescence, phenomenon collective initiated by intense pulses free-electron lasers, is developed based on stochastic partial differential equations. The equations are derived from first principles, relevant approximations, derivation steps, extensions specific stimulated presented. resulting take form three-dimensional generalized Maxwell-Bloch augmented with noise terms for both field atomic variables....
In this work, we describe the instrumentation used to perform first operando transmission X-ray microscopy (TXM) and simultaneous diffraction of laser melting simulating powder bed fusion on XCS instrument at Linac Coherent Light Source (LCLS) free-electron (XFEL). Our TXM with 40× magnification in regime 11 keV gave spatial resolutions down 940 nm per line pair, effective pixel sizes 206 nm, image integration times <100 fs, frame rates tunable between 2.1 119 ns for two probe frames (0.48...
We present a numerical study of the process kink-antikink collisions in coupled one-dimensional two-component $\phi^4$ model. Our results reveal two different soliton solutions which represent double kink configuration and kink-non-topological (lump) bound state. Collision these solitons leads to very reach resonance structure is related reversible energy exchange between kinks, non-topological internal vibrational modes. Various channels are discussed, it shown there new type self-similar...
We study boundary scattering in the ϕ 4 model on a half-line with oneparameter family of Neumann-type conditions. A rich variety phenomena is observed, which extends previously-studied behaviour full line to include regimes near-elastic scattering, restoration missing window, and creation kink or oscillon through collision-induced decay metastable state. also vibrational mode, explore different scenarios for its relaxation kinks.
Significance An X-ray oscillator generating fully coherent pulses at the characteristic length and time scale of atomic molecular phenomena, angstrom wavelength, femtosecond duration has been a dream laser physics from 1960s. The paper presents study an based on population inversion <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mi>K</mml:mi> <mml:mi>α</mml:mi> </mml:math> electrons in transition-metal compound, coherent, transform-limited, high-power...
We present an x-ray regenerative amplifier free-electron laser design capable of producing fully coherent hard pulses across a broad tuning range at high steady state repetition rate. The scheme leverages strong undulator taper and apertured diamond output-coupling cavity crystal to produce both peak average spectral brightness radiation that is 2 3 orders magnitude greater than conventional single-pass self-amplified spontaneous emission amplifiers. Refractive guiding in the postsaturation...
X-ray Free Electron Lasers provide femtosecond x-ray pulses with narrow bandwidth and unprecedented peak brightness. Special modes of operation have been developed to deliver double for pump, probe experiments. However, the longest delay between two achieved existing single bucket methods is less than 1 picosecond, thus preventing exploration longer time-scale dynamics. We present a novel two-bucket scheme covering delays from 350 picoseconds hundreds nanoseconds in discrete steps...
The feasibility of generating X-ray pulses in the 4–8 keV fundamental photon energy range with 0.65 TW peak power, 15 fs pulse duration and 9 × 10 −5 bandwidth using LCLS-II copper linac hard (HXR) undulator is shown. In addition, third-harmonic 8–12 GW power narrow are also generated. High-power small-bandwidth X-rays obtained two electron bunches separated by about 1 ns, one to generate a high-power seed signal, other amplify it through process HXR tapering. bunch delay compensated...
Background Homebound older adults are a high-risk group for depression. However, many of them face barriers to accessing evidence-supported mental health treatments. Digital interventions can potentially improve treatment access, but few web-based explicitly tailored depression in adults. Objective This paper describes the development process Empower@Home, web-delivered intervention homebound that is based on cognitive behavioral therapy, and reports outcomes usability studies. Methods...
X-ray free-electron lasers (XFELs) provide intense pulses that can generate stimulated emission, a phenomenon has been observed and studied in materials ranging from neon to copper. Two schemes have employed: amplified spontaneous emission (ASE) seeded (SSE), where second color XFEL pulse provides the seed. Both phenomena are currently explored for coherent laser sources spectroscopy. Here, we report measurements of ASE SSE 5.9 keV Mn K α 1 fluorescence line 3.9 molar NaMnO 4 solution,...
Significance The generation of phase-stable femtosecond X-ray pulse pairs will advance nonlinear spectroscopies and imaging, providing direct insight into the coupled motions electrons nuclei with resolution on electronic length scale timescale. This paper presents such in domain. approach uses free-electron laser pulses to induce highly directional, intense, superfluorescence seeded stimulated emission at 5.9 keV manganese Kα 1 line. finding is evidenced by strong interference fringes signals.
A common issue encountered in photoemission electron sources used accelerators is the transverse inhomogeneity of laser distribution resulting from laser-amplification process and often use frequency up conversion nonlinear crystals. inhomogeneous on photocathode produces charged beams with lower beam quality. In this paper, we explore possible microlens arrays (fly-eye light condensers) to dramatically improve uniformity drive pulse UV photocathodes. We also demonstrate such generate...
We discuss how internal rotation with fixed angular frequency can affect the solitons in baby Skyrme model which global O(3) symmetry is broken to SO(2). Two particular choices of potential term are considered, "old" and "new" double vacuum potential, do not impose any assumptions about on fields. Our results confirm existence two types instabilities determined by relation between mass parameter frequency.
Generally, turn-to-turn power fluctuations of incoherent spontaneous synchrotron radiation in a storage ring depend on the 6D phase-space distribution electron bunch. In some cases, if only one parameter is unknown, this can be determined from measured magnitude these fluctuations. Letter, we report an absolute measurement (no free parameters or calibration) small vertical emittance (5–15 nm rms) flat beam by method, under conditions, when it unresolvable conventional light size...
We present measurements of X-ray Parametric Down Conversion at the Advanced Photon Source synchrotron facility. Using an incoming pump beam 22 keV, we observe simultaneous, elastic emission down-converted photon pairs generated in a diamond crystal. The are detected using high count rate silicon drift detectors with low noise. Production by down-conversion is confirmed measuring time-energy correlations detector signal, where within energy window ranging from 10 to 12 keV only observed short...
We describe a new method to produce intensity stable, highly coherent, narrow-band x-ray pulses in self-seeded free electron (FEL) lasers. The approach uses an ultra-short beam generate single spike FEL pulse with wide coherent bandwidth. self-seeding monochromator then notches out narrow spectral region of this be amplified by long portion full saturation. In contrast typical where monochromatization noisy SASE leads either large fluctuations or multiple frequencies, we show that produces...
In a storage ring, turn-to-turn fluctuations in the intensity of spontaneous synchrotron radiation occur due to two mechanisms. The first mechanism is quantum uncertainty number emitted photons. second variations relative positions classical pointlike electrons bunch. We present unified description both effects framework optics. derive an equation for arbitrary degree coherence, which generalizes previously reported results temporally incoherent radiation. compare predictions our calculation...
Stanford Synchrotron Radiation Lightsource serves a wide scientific community with its variety of X-ray capabilities. Recently, wiggler source located at beamline 10-2 has been employed to perform high-resolution rocking curve imaging (RCI) diamond and silicon crystals. RCI is invaluable for the development upcoming cavity-based sources SLAC, including free-electron laser oscillator. In this paper, apparatus described experimental results are provided validate design. Future improvements...
High-gain free-electron lasers (FELs) are becoming important light sources at short wavelengths such as the EUV and x-ray regimes. A particularly promising concept is regenerative amplifier FEL (RAFEL), which can greatly increase brightness stability of a single pass device. One critical challenges RAFEL maintaining electron-optical overlap over relatively large (hundreds meters) footprint system. Numerical modeling RAFELs with angular positional errors for designing stable cavities, well to...