A5041118628- Laser-Plasma Interactions and Diagnostics
- High-pressure geophysics and materials
- Laser-induced spectroscopy and plasma
- Atomic and Molecular Physics
- Advanced X-ray Imaging Techniques
- Diamond and Carbon-based Materials Research
- Laser-Matter Interactions and Applications
- High-Velocity Impact and Material Behavior
- Ion-surface interactions and analysis
- X-ray Spectroscopy and Fluorescence Analysis
- Laser Design and Applications
- Crystallography and Radiation Phenomena
- Energetic Materials and Combustion
- Laser Material Processing Techniques
- Metal and Thin Film Mechanics
- Microstructure and mechanical properties
- Nuclear Physics and Applications
- Particle Accelerators and Free-Electron Lasers
- Advanced Electron Microscopy Techniques and Applications
- Plasma Diagnostics and Applications
- Boron and Carbon Nanomaterials Research
- Force Microscopy Techniques and Applications
- Thermography and Photoacoustic Techniques
- Dust and Plasma Wave Phenomena
- X-ray Diffraction in Crystallography
University of Oxford
2016-2025
Lawrence Livermore National Laboratory
1997-2021
Atomic Weapons Establishment
2006-2021
University College London
2018
University of Rochester
1986-2017
Energetics (United States)
1986-2017
University of York
1996-2017
Charles University
2017
Oxford Brookes University
2009
Czech Academy of Sciences, Institute of Physics
2009
The motion of atoms on interatomic potential energy surfaces is fundamental to the dynamics liquids and solids. An accelerator-based source femtosecond x-ray pulses allowed us follow directly atomic displacements an optically modified landscape, leading eventually transition from crystalline solid disordered liquid. We show that, first order in time, are inertial, we place constraints shape curvature transition-state surface. Our measurements point toward analogies between this...
Distorted Nanoparticle Nanoparticles have found many applications in modern technology; however, the full characterization of individual particles is challenging. One most interesting mechanical properties particle's response to lattice distortion. This property has been probed for ensembles nanoparticles, but required averaging may distort results. Clark et al. (p. 56 , published online 23 May; see Perspective by Hartland and Lo ) were able image generation subsequent evolution coherent...
We have used the Linac Coherent Light Source to generate solid-density aluminum plasmas at temperatures of up 180 eV. By varying photon energy x rays that both create and probe plasma, observing K-α fluorescence, we can directly measure position K edge highly charged ions within system. The results are found disagree with predictions extensively Stewart-Pyatt model, but consistent earlier model Ecker Kröll, which predicts significantly greater depression ionization potential.
Time-resolved x-ray diffraction with picosecond temporal resolution is used to observe scattering from impulsively generated coherent acoustic phonons in laser-excited InSb crystals. The observed frequencies and damping rates are agreement a model based on dynamical theory coupled analytic solutions for the laser-induced strain profile. results consistent 12 ps thermal electron-acoustic phonon coupling time together an instantaneous component deformation-potential interaction. Above critical...
The generation of high harmonics created during the interaction a 2.5 ps, 1053 nm laser pulse with solid target has been recorded for intensities up to ${10}^{19}\mathrm{W}{\mathrm{cm}}^{\ensuremath{-}2}$. Harmonic orders 68th at 15.5 in first order have observed indications 75th 14.0 second-order diffraction. No differences harmonic emission between $s$ and $p$ polarization beam were observed. power 38th 27.7 is estimated be 24 MW.
In situ x-ray diffraction studies of iron under shock conditions confirm unambiguously a phase change from the bcc (alpha) to hcp (epsilon) structure. Previous identification this transition in shock-loaded has been inferred correlation between shock-wave-profile analyses and static high-pressure measurements. This is intrinsically limited because dynamic loading can markedly affect structural modifications solids. The measurements are consistent with uniaxial collapse along [001] direction...
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...
When a laser pulse of intensity 10(19) W cm(-2) interacts with solid targets, electrons energies some tens MeV are produced. In tantalum target, the generate an intense highly directional gamma-ray beam that can be used to carry out photonuclear reactions. The isotopes 11C, 38K, (62,64)Cu, 63Zn, 106Ag, 140Pr, and 180Ta have been produced by (gamma,n) reactions using VULCAN beam. addition, laser-induced nuclear fission in 238U has demonstrated, process which was theoretically predicted at...
The angular distribution of bremsstrahlung gamma rays produced by fast electrons accelerated in relativistic laser-solid interaction has been studied photoneutron activation copper. We show that the gamma-ray beam moves from target normal to direction k(laser) vector as scale length is increased. Similar behavior found also 2D particle-in-cell simulations.
Novel measurements of electromagnetic radiation above 10 MeV are presented for ultra intense laser pulse interactions with solids. A bright, highly directional source γ rays was observed directly behind the target. The were produced by bremsstrahlung from energetic electrons generated during interaction. They measured using photoneutron reaction [63Cu(γ,n)62Cu] in copper. resulting activity coincidence counting positron annihilation which decay Cu62. New at 1019 W cm−2 also presented.
The ultrafast evolution of microstructure is key to understanding high-pressure and strain-rate phenomena. However, the visualization lattice dynamics at scales commensurate with those atomistic simulations has been challenging. Here, we report femtosecond x-ray diffraction measurements unveiling response copper laser shock-compression peak normal elastic stresses ~73 gigapascals (GPa) strain rates 10(9) per second. We capture from a one-dimensional (1D) 3D plastically relaxed state within...
The propagation of shock waves through polycrystalline iron is explored by large-scale atomistic simulations. For large enough strengths the passage wave causes body-centered-cubic phase to transform into a close-packed with most structure being isotropic hexagonal-close-packed (hcp) and, depending on strength and grain orientation, some fraction face-centered-cubic (fcc) structure. simulated Hugoniot compared experiments. By calculating extended x-ray absorption fine (EXAFS) directly from...
Abstract The effect of a dense plasma environment on the energy levels an embedded ion is usually described in terms lowering its continuum level. For strongly coupled plasmas, phenomenon intimately related to equation state; hence, accurate treatment crucial for most astrophysical and inertial-fusion applications, where case mixtures particular interest. Here we present experiment showing that standard density-dependent analytical models are inadequate describe solid-density plasmas at...
Abstract The advent of hard x-ray free-electron lasers (XFELs) has opened up a variety scientific opportunities in areas as diverse atomic physics, plasma nonlinear optics the range and protein crystallography. In this article, we access new field science by measuring quantitatively local bulk properties dynamics matter under extreme conditions, case using short XFEL pulse to image an elastic compression wave diamond. was initiated intense optical laser imaged at different delay times after...
We present measurements on <a:math xmlns:a="http://www.w3.org/1998/Math/MathML"><a:mrow><a:msub><a:mi>Fe</a:mi><a:mn>2</a:mn></a:msub><a:msub><a:mi mathvariant="normal">O</a:mi><a:mn>3</a:mn></a:msub></a:mrow></a:math> amorphization and melt under laser-driven shock compression up to 209(10) GPa via time-resolved x-ray diffraction. At 122(3) GPa, a diffuse signal is observed indicating the presence of noncrystalline phase. Structure factors have been extracted 182(6) showing two well-defined...