A5003475811- Laser-Matter Interactions and Applications
- Advanced Chemical Physics Studies
- Spectroscopy and Quantum Chemical Studies
- Mass Spectrometry Techniques and Applications
- Photochemistry and Electron Transfer Studies
- Advanced X-ray Imaging Techniques
- Atomic and Molecular Physics
- X-ray Spectroscopy and Fluorescence Analysis
- Advanced Electron Microscopy Techniques and Applications
- Spectroscopy and Laser Applications
- Molecular spectroscopy and chirality
- Electron and X-Ray Spectroscopy Techniques
- Photoreceptor and optogenetics research
- Laser Design and Applications
- Analytical Chemistry and Chromatography
- Force Microscopy Techniques and Applications
- Nuclear Physics and Applications
- Molecular Junctions and Nanostructures
- Surface Chemistry and Catalysis
- Mechanical and Optical Resonators
- Radical Photochemical Reactions
- Random lasers and scattering media
- Laser-Plasma Interactions and Diagnostics
- Advanced Fiber Laser Technologies
- Terahertz technology and applications
SLAC National Accelerator Laboratory
2018-2024
Vescent Photonics (United States)
2024
Lawrence Berkeley National Laboratory
2016-2022
University of California, Berkeley
2016-2020
Menlo School
2020
Berkeley College
2018
Advanced Technology Group (Czechia)
2018
In quantum systems, coherent superpositions of electronic states evolve on ultrafast timescales (few femtosecond to attosecond, 1 as = 0.001 fs 10^{-18} s), leading a time dependent charge density. Here we exploit the first attosecond soft x-ray pulses produced by an free-electron laser induce core-hole excitation in nitric oxide. Using additional circularly polarized infrared pulse create clock time-resolve electron dynamics, and demonstrate control motion tuning photon energy pulse....
Free-electron lasers provide a source of x-ray pulses short enough and intense to drive nonlinearities in molecular systems. Impulsive interactions driven by these way create probe valence electron motions with high temporal spatial resolution. Observing electronic is crucial understand the role coherence chemical processes. A simple nonlinear technique for probing motion, impulsive stimulated Raman scattering (ISXRS), involves single interaction produce coherent superposition states. We...
Directly imaging structural dynamics involving hydrogen atoms by ultrafast diffraction methods is complicated their low scattering cross sections. Here we demonstrate that megaelectronvolt electron sufficiently sensitive to follow in isolated molecules. In a study of the photodissociation gas phase ammonia, simultaneously observe signatures nuclear and corresponding electronic structure changes resulting from dissociation time-dependent diffraction. Both assignments are confirmed ab initio...
Conformational isomers or conformers of molecules play a decisive role in chemistry and biology. However, experimental methods to investigate chemical reaction dynamics are typically not conformer-sensitive. Here, we report on gas-phase megaelectronvolt ultrafast electron diffraction investigation {\alpha}-phellandrene undergoing an electrocyclic ring-opening reaction. We directly image the evolution specific set into product isomer predicted by Woodward-Hoffmann rules real space time. Our...
Abstract The double photoionization of a molecule by one photon ejects two electrons and typically creates an unstable dication. Observing the subsequent fragmentation products in coincidence can reveal surprisingly detailed picture dynamics. Determining time evolution quantum mechanical states involved leads to deeper understanding molecular Here combined experimental theoretical study, we unambiguously separate sequential breakup via D + OD intermediates, from other processes leading same...
Abstract Electrocyclic reactions are characterized by the concerted formation and cleavage of both σ π bonds through a cyclic structure. This structure is known as pericyclic transition state for thermal minimum in excited photochemical reactions. However, geometry has yet to be observed experimentally. We use combination ultrafast electron diffraction wavepacket simulations image structural dynamics electrocyclic ring-opening reaction molecule α-terpinene. The motion into dominated...
We present a measurement of the time-resolved photoelectron kinetic energy spectrum ethylene using 156 nm and 260 laser pulses. The pulse first excites to 1B1u (ππ∗) electronic state where light photoionizes system probe relaxation dynamics with sub-30 fs resolution. Recent ab initio calculations by Mori et al. [J. Phys. Chem. A 116, 2808-2818 (2012)] have predicted an ultrafast population transfer from initially excited low-lying Rydberg during photoexcited ethylene. measured reveals wave...
Manipulating the atomic and electronic structure of matter with strong terahertz (THz) fields while probing response ultrafast pulses at x-ray free electron lasers (FELs) has offered unique insights into a multitude physical phenomena in solid state physics. Recent upgrades FEL facilities are pushing to much higher repetition rates, enabling unprecedented signal noise for pump probe experiments. This requires development suitable THz sources that able deliver intense compatible rates. Here...
We present the design of an electron velocity map imaging (VMI) spectrometer where ionizing laser source propagates along symmetry axis spectrometer. The co-axial geometry is useful in a variety experiments, because it provides unique 2-dimensional projection 3-dimensional momentum distribution. Initial simulations show that this VMI can work with both high energy (more than 100 eV) and low (tens electrons. demonstrate performance at Linac Coherent Light Source X-ray Free Electron Laser facility.
The recent demonstration of isolated attosecond pulses from an X-ray free-electron laser (XFEL) opens the possibility for probing ultrafast electron dynamics at wavelengths. An established experimental method is transient absorption spectroscopy, where spectrum measured by scanning central photon energy and recording resultant photoproducts. spectral bandwidth inherent to wide compared resonant features typically probed, which generally precludes application this technique in regime. In...
The structural dynamics of photoexcited gas-phase carbon disulfide (CS2) molecules are investigated using ultrafast electron diffraction. were triggered by excitation the optically bright 1B2(1Σu+) state an ultraviolet femtosecond laser pulse centred at 200 nm. In accordance with previous studies, rapid vibrational motion facilitates a combination internal conversion and intersystem crossing to lower-lying electronic states. Photodissociation via these manifolds results in production CS...
The newly constructed time-resolved atomic, molecular and optical science instrument (TMO) is configured to take full advantage of both linear accelerators at SLAC National Accelerator Laboratory, the copper accelerator operating a repetition rate 120 Hz providing high per-pulse energy as well superconducting about 1 MHz average intensity. Both power soft X-ray free-electron laser with new variable-gap undulator section. With this flexible light source, TMO supports many experimental...
<title>Abstract</title> Photoinduced biological and chemical reactions are often based on key structural transformations of a molecule driven across multiple electronic states. Acetylacetone (AcAc) is prototypical system for complex pathways involving several conical intersections (CI) singlet-triplet intersystem crossings (ISC) characterized by distinct geometries. In the gas phase, AcAc predominantly in planar ring-like enolic form stabilized strong intramolecular O-H∙∙∙O hydrogen bond....
An ultrafast electron diffraction study of the structural dynamics cis , -1,3-cyclooctadiene has identified a ring stretching distortion as new reaction coordinate molecule transitions from excited state back to ground state.
Abstract X-ray photoelectron spectroscopy (XPS) measures the binding energy of core-level electrons, which are well-localised to specific atomic sites in a molecular system, providing valuable information on local chemical environment. The technique relies measuring spectrum upon x-ray photoionisation, and resolution is often limited by bandwidth ionising pulse. This particularly problematic for time-resolved XPS, where desired time enforces fundamental lower limit source. In this work, we...
We present a combined experimental and theoretical investigation of the electron dynamics body-frame angular dependence valence photo-single ionization CF4 subsequent dissociation into CF3+ F. Ionization from t2 orbital shows overlapping shape resonances close to threshold that couple same total symmetry, leading striking changes in photoelectron distributions when viewed body-frame.
We investigate ultrafast dynamics of the lowest singlet excited electronic state in liquid nitrobenzene using Ultrafast Transient Polarization Spectroscopy (UTPS), extending well-known technique Optical-Kerr Effect (OKE) spectroscopy to states. The third-order non-linear response molecular ensemble is highly sensitive details character and geometries measured two femtosecond pulses following a third pulse that populates S1 state. By measuring this as function time delays between three...
We have conducted an experimental study on the photo double ionization (PDI) of carbon-dioxide dimers at photon energies 37 and 55 eV oxygen 38, 41.5, 46 eV, while focusing dissociation dynamics upon single-photon absorption. The investigation was performed by applying cold-target recoil-ion momentum spectroscopy method in order to collect record three-dimensional momenta ionic fragments emitted electrons from dissociating dimer coincidence. kinetic-energy release fragmentation electron...
The electronic and nuclear dynamics in methanol, following 156~nm photoexcitation, are investigated by combining a detailed analysis of time-resolved photoelectron spectroscopy experiments with structure calculations. photoexcitation pump pulse is followed delayed 260~nm photoionization probe pulse, to produce photoelectrons that analyzed velocity map imaging. yield mass-resolved ions, measured similar experimental conditions, found exhibit the same time-dependence as specific spectral...
The authors reveal how the emitted photoelectron influences localization process of remaining electron in a dissociating diatomic molecular cation upon single photo ionization via retroactive Coulomb interaction. dependence asymmetric emission pattern frame on kinetic energy release heavy fragments and is studied.
This paper presents a state-selective analysis on the photoionization mechanisms and fragmentation dynamics of H${}^{+}$ + dissociation channel in NH${}_{3}$ upon direct single-photon double ionization.
We report the reflectance, ~1° from normal incidence, of six different mirrors as a function photon energy, using monochromatic vacuum ultraviolet (VUV) and extreme (XUV) radiation with energies between 7.5 eV 24.5 eV. The examined included both single multilayer optical coatings, well an uncoated substrate. discuss performance each mirror, paying particular attention to potential application suppression selection high-order harmonics Ti:sapphire laser.
We present state-selective measurements on the NH$_2^{+}$ + H$^{+}$ and NH$^{+}$ H dissociation channels following single-photon double ionization at 61.5 eV of neutral NH$_{3}$, where two photoelectrons cations are measured in coincidence using 3-D momentum imaging. Three dication electronic states identified to contribute channel, excitation one three undergoes intersystem crossing prior dissociation, producing a cold NH$_2^+$ fragment. In contrast, other directly dissociate,...