publications

2025

1. Experimental Generation of Extreme Electron Beams for Advanced Accelerator Applications

   C. Emma, N. Majernik, K. K. Swanson, and 13 more authors

   Phys. Rev. Lett., Feb 2025

   DOI
2. Probing Electronic Coherence between Core-Level Vacancies at Different Atomic Sites

   Jun Wang, Taran Driver, Paris L. Franz, and 30 more authors

   Phys. Rev. X, Jan 2025

   DOI
3. Spectrotemporal Shaping of Attosecond X-Ray Pulses with a Fresh-Slice Free-Electron Laser

   River R. Robles, Kirk A. Larsen, David Cesar, and 14 more authors

   Phys. Rev. Lett., Mar 2025

   DOI
4. Imaging the photochemistry of cyclobutanone using ultrafast electron diffraction: Experimental results

   A. E. Green, Y. Liu, F. Allum, and 27 more authors

   The Journal of Chemical Physics, May 2025

   Abs DOI

   We investigated the ultrafast structural dynamics of cyclobutanone following photoexcitation at λ = 200 nm using gas-phase megaelectronvolt ultrafast electron diffraction. Our investigation complements the simulation studies of the same process within this special issue. It provides information about both electronic state population and structural dynamics through well-separable inelastic and elastic electron scattering signatures. We observe the depopulation of the photoexcited S2 state of cyclobutanone with n3s Rydberg character through its inelastic electron scattering signature with a time constant of (0.29 ± 0.2) ps toward the S1 state. The S1 state population undergoes ring-opening via a Norrish Type-I reaction, likely while passing through a conical intersection with S0. The corresponding structural changes can be tracked by elastic electron scattering signatures. These changes appear with a delay of (0.14 ± 0.05) ps with respect to the initial photoexcitation, which is less than the S2 depopulation time constant. This behavior provides evidence for the ballistic nature of the ring-opening once the S1 state is reached. The resulting biradical species react further within (1.2 ± 0.2) ps via two rival fragmentation channels yielding ketene and ethylene, or propene and carbon monoxide. Our study showcases the value of both gas-phase ultrafast diffraction studies as an experimental benchmark for nonadiabatic dynamics simulation methods and the limits in the interpretation of such experimental data without comparison with such simulations.

5. Characterizing few-cycle UV resonant dispersive waves through direct field sampling

   Kirk A. Larsen, Christopher Lantigua, Chelsea Kincaid, and 15 more authors

   Opt. Lett., Aug 2025

   Abs DOI

   We demonstrate compression of few-cycle ultraviolet (UV) resonant dispersive waves (RDWs) generated in a cascaded hollow capillary fiber setup using a Yb laser system. Temporal characterization is performed using both tunneling ionization with a perturbation for the time-domain observation of an electric field (TIPTOE) and self-diffraction frequency-resolved optical gating (SD-FROG), which show good agreement. Through careful dispersion management, we compress the RDW pulse to 6.9 fs at a \sim390-nm central wavelength. This is the first, to our knowledge, measurement of an RDW using the TIPTOE method and demonstrates the viability of this technique to reliably characterize few-cycle UV pulses with \muJ pulse energies.

6. Imaging Valence Electron Rearrangement in a Chemical Reaction Using Hard X-Ray Scattering

   Ian Gabalski, Alice Green, Philipp Lenzen, and 24 more authors

   Phys. Rev. Lett., Aug 2025

   DOI

2024

1. The Linac Coherent Light Source II photoinjector laser infrastructure

   Hao Zhang, Sasha Gilevich, Alan Miahnahri, and 23 more authors

   High Power Laser Science and Engineering, Aug 2024

   e51

   Abs DOI

   This paper presents a comprehensive technical overview of the Linac Coherent Light Source II (LCLS-II) photoinjector laser system, its first and foremost component. The LCLS-II photoinjector laser system serves as an upgrade to the original LCLS at SLAC National Accelerator Laboratory. This advanced laser system generates high-quality laser beams for the LCLS-II, contributing to the instrument’s unprecedented brightness, precision and flexibility. Our discussion extends to the various subsystems that comprise the photoinjector, including the photocathode laser, laser heater and beam transport systems. Lastly, we draw attention to the ongoing research and development infrastructure underway to enhance the functionality and efficiency of the LCLS-II, and similar X-ray free-electron laser facilities around the world, thereby contributing to the future of laser technology and its applications.

2. Attosecond-pump attosecond-probe x-ray spectroscopy of liquid water

   Shuai Li, Lixin Lu, Swarnendu Bhattacharyya, and 23 more authors

   Science, Aug 2024

   Abs DOI

   Attosecond-pump/attosecond-probe experiments have long been sought as the most straightforward method for observing electron dynamics in real time. Although there has been much success with overlapped near-infrared femtosecond and extreme ultraviolet attosecond pulses combined with theory, true attosecond-pump/attosecond-probe experiments have been limited. We used a synchronized attosecond x-ray pulse pair from an x-ray free-electron laser to study the electronic response to valence ionization in liquid water through all x-ray attosecond transient absorption spectroscopy (AX-ATAS). Our analysis showed that the AX-ATAS response is confined to the subfemtosecond timescale, eliminating any hydrogen atom motion and demonstrating experimentally that the 1b1 splitting in the x-ray emission spectrum is related to dynamics and is not evidence of two structural motifs in ambient liquid water. The low intensity of attosecond pulses remains one of the main challenges in conducting true attosecond-pump/attosecond-probe experiments that could directly observe electron dynamics in real time when all nuclear motions are frozen. Using a recently upgraded x-ray free-electron laser that enables the production and synchronization of two-color attosecond x-ray pulse pairs, Li et al. performed all x-ray attosecond transient absorption spectroscopy measurements on an important condensed phase process: the initial electronic response to valence ionization in liquid water. This work experimentally resolves a long-standing debate around the interpretation of the 1b1 x-ray emission doublet. The presented technique could resolve many complex condensed phase issues for which nuclear motions need to be frozen to capture the information content of the probe signal. —Yury Suleymanov Liquid water was studied using pure x-ray pulses at the subfemtosecond time scale.

3. Experimental demonstration of attosecond pump–probe spectroscopy with an X-ray free-electron laser

   Zhaoheng Guo, Taran Driver, Sandra Beauvarlet, and 47 more authors

   Nature Photonics, Jul 2024

   Abs DOI

   Pump–probe experiments with subfemtosecond resolution are the key to understanding electronic dynamics in quantum systems. Here we demonstrate the generation and control of subfemtosecond pulse pairs from a two-colour X-ray free-electron laser. By measuring the delay between the two pulses with an angular streaking diagnostic, we characterize the group velocity of the X-ray free-electron laser and show control of the pulse delay down to 270\thinspaceas. We confirm the application of this technique to a pump–probe measurement in core-ionized para-aminophenol. These results reveal the ability to perform pump–probe experiments with subfemtosecond resolution and atomic site specificity.

4. Terawatt-scale attosecond X-ray pulses from a cascaded superradiant free-electron laser

   Paris Franz, Siqi Li, Taran Driver, and 22 more authors

   Nature Photonics, Jul 2024

   Abs DOI

   Intense attosecond X-ray pulses are key for ultrafast nonlinear spectroscopy and diffractive imaging. Here we demonstrate the generation of terawatt-scale isolated attosecond pulses with a two-stage cascaded X-ray free-electron laser. These pulses have a median energy in excess of 100\thinspace\muJ in the soft X-ray region. The temporal profile is characterized with an angular streaking measurement, revealing a maximum peak power of 1.1\thinspaceTW. Our data show an increase in the average peak power of attosecond X-ray pulses by one order of magnitude over previous reported results and provide strong evidence of soliton-like superradiant behaviour in the X-ray regime.

5. Wavelength scaling and multicolor operation of a plasma-driven attosecond x-ray source via harmonic generation

   Rafi Hessami, Jenny Morgan, River Robles, and 3 more authors

   Phys. Rev. Accel. Beams, Jul 2024

   DOI
6. Tracking ultrafast non-adiabatic dissociation dynamics of the deuterated water dication molecule

   W. Iskandar, T. N. Rescigno, A. E. Orel, and 13 more authors

   The Journal of Chemical Physics, Jul 2024

   Abs DOI

   We applied reaction microscopy to elucidate fast non-adiabatic dissociation dynamics of deuterated water molecules after direct photo-double ionization at 61 eV with synchrotron radiation. For the very rare D+ + O+ + D breakup channel, the particle momenta, angular, and energy distributions of electrons and ions, measured in coincidence, reveal distinct electronic dication states and their dissociation pathways via spin–orbit coupling and charge transfer at crossings and seams on the potential energy surfaces. Notably, we could distinguish between direct and fast sequential dissociation scenarios. For the latter case, our measurements reveal the geometry and orientation of the deuterated water molecule with respect to the polarization vector that leads to this rare 3-body molecular breakup channel. Aided by multi-reference configuration-interaction calculations, the dissociation dynamics could be traced on the relevant potential energy surfaces and particularly their crossings and seams. This approach also unraveled the ultrafast time scales governing these processes.

7. Quantitative x-ray scattering of free molecules

   Lingyu Ma, Nathan Goff, Andrés Moreno Carrascosa, and 22 more authors

   Journal of Physics B: Atomic, Molecular and Optical Physics, Sep 2024

   Abs DOI

   Advances in x-ray free electron lasers have made ultrafast scattering a powerful method for investigating molecular reaction kinetics and dynamics. Accurate measurement of the ground-state, static scattering signals of the reacting molecules is pivotal for these pump-probe x-ray scattering experiments as they are the cornerstone for interpreting the observed structural dynamics. This article presents a data calibration procedure, designed for gas-phase x-ray scattering experiments conducted at the Linac Coherent Light Source x-ray Free-Electron Laser at SLAC National Accelerator Laboratory, that makes it possible to derive a quantitative dependence of the scattering signal on the scattering vector. A self-calibration algorithm that optimizes the detector position without reference to a computed pattern is introduced. Angle-of-scattering corrections that account for several small experimental non-idealities are reported. Their implementation leads to near quantitative agreement with theoretical scattering patterns calculated with ab-initio methods as illustrated for two x-ray photon energies and several molecular test systems.

8. Attosecond impulsive stimulated X-ray Raman scattering in liquid water

   Oliver Alexander, Felix Egun, Laura Rego, and 35 more authors

   Science Advances, Sep 2024

   Abs DOI

   We report the measurement of impulsive stimulated x-ray Raman scattering in neutral liquid water. An attosecond pulse drives the excitations of an electronic wavepacket in water molecules. The process comprises two steps: a transition to core-excited states near the oxygen atoms accompanied by transition to valence-excited states. Thus, the wavepacket is impulsively created at a specific atomic site within a few hundred attoseconds through a nonlinear interaction between the water and the x-ray pulse. We observe this nonlinear signature in an intensity-dependent Stokes Raman sideband at 526 eV. Our measurements are supported by our state-of-the-art calculations based on the polarization response of water dimers in bulk solvation and propagation of attosecond x-ray pulses at liquid density. Attosecond x-ray pulses create time and space localized electronic excitations in water that are read-out in the x-ray signal.

9. “Beam à la carte”: Laser heater shaping for attosecond pulses in a multiplexed x-ray free-electron laser

   Siqi Li, Zhen Zhang, Shawn Alverson, and 19 more authors

   Applied Physics Letters, Nov 2024

   Abs DOI

   Electron beam shaping allows the control of the temporal properties of x-ray free-electron laser pulses from femtosecond to attosecond timescales. Here, we demonstrate the use of a laser heater to shape electron bunches and enable the generation of attosecond x-ray pulses. We demonstrate that this method can be applied in a selective way, shaping a targeted subset of bunches while leaving the remaining bunches unchanged. This experiment enables the delivery of shaped x-ray pulses to multiple undulator beamlines, with pulse properties tailored to specialized scientific applications.

10. Design and performance of a magnetic bottle electron spectrometer for high-energy photoelectron spectroscopy

    Kurtis Borne, Jordan T. O’Neal, Jun Wang, and 19 more authors

    Review of Scientific Instruments, Dec 2024

    Abs DOI

    We describe the design and performance of a magnetic bottle electron spectrometer (MBES) for high-energy electron spectroscopy. Our design features a 2 m long electron drift tube and electrostatic retardation lens, achieving sub-electronvolt (eV) electron kinetic energy resolution for high energy (several hundred eV) electrons with a close to 4π collection solid angle. A segmented anode electron detector enables the simultaneous collection of photoelectron spectra in high resolution and high collection efficiency modes. This versatile instrument is installed at the time-resolved molecular and optical sciences instrument at the Linac Coherent Light Source x-ray free-electron laser (XFEL). In this paper, we demonstrate its high resolution, collection efficiency, and spatial selectivity in measurements where it is coupled to an XFEL source. These combined characteristics are designed to enable high-resolution time-resolved measurements using x-ray photoelectron, absorption, and Auger–Meitner spectroscopy. We also describe the pervasive artifact in MBES time-of-flight spectra that arises from a periodic modulation in electron collection efficiency and present a robust analysis procedure for its removal.

2023

1. Atomic autoionization in the photo-dissociation of super-excited deuterated water molecules fragmenting into D+ + O+ + D

   W. Iskandar, T. N. Rescigno, A. E. Orel, and 10 more authors

   Phys. Chem. Chem. Phys., Dec 2023

   Abs DOI

   We present the relaxation dynamics of deuterated water molecules via autoionization, initiated by the absorption of a 61 eV photon, producing the very rare D+ + O+ + D breakup channel. We employ the COLd target recoil ion momentum spectroscopy method to measure the 3D momenta of the ionic fragments and emitted electrons from the dissociating molecule in coincidence. We interpret the results using the potential energy surfaces extracted from multi-reference configuration interaction calculations. The measured particle energy distributions can be related to a super-excited monocationic state located above the double ionization threshold of D2O. The autoionized electron energy shows a sharp distribution centered around 0.5 eV, which is a signature of the atomic oxygen autoionization occurring in the direct and sequential dissociation processes of D2O+* at a large internuclear distance. In this way, an O+ radical fragment and a low-energy electron are created, both of which can trigger secondary reactions in their environment.

2. Strongly coupled intermediate electronic states in one-color two-photon single valence ionization of O2

   Kirk A. Larsen, Roger Y. Bello, Robert R. Lucchese, and 3 more authors

   The Journal of Chemical Physics, Jan 2023

   Abs DOI

   We present an experimental and theoretical energy- and angle-resolved investigation on the non-dissociative photoionization dynamics of near-resonant, one-color, two-photon, single valence ionization of neutral O2 molecules. Using 9.3 eV femtosecond pulses produced via high harmonic generation and a 3-D momentum imaging spectrometer, we detect the photoelectrons and O2+ cations produced from one-color, two-photon ionization in coincidence. The measured and calculated photoelectron angular distributions show agreement, which indicates that a superposition of two intermediate electronic states is dominantly involved and that wavepacket motion on those near-resonantly populated intermediate states does not play a significant role in the measured two-photon ionization dynamics. Here, we find greater utility in the diabatic representation compared to the adiabatic representation, where invoking a single valence-character diabat is sufficient to describe the underlying two-photon ionization mechanism.

3. Efficiency of charge transfer in changing the dissociation dynamics of OD+ transients formed after the photo-fragmentation of D2O

   W. Iskandar, T. N. Rescigno, A. E. Orel, and 13 more authors

   The Journal of Chemical Physics, Sep 2023

   Abs DOI

   We present an investigation of the relaxation dynamics of deuterated water molecules after direct photo-double ionization at 61 eV. We focus on the very rare D+ + O+ + D reaction channel in which the sequential fragmentation mechanisms were found to dominate the dynamics. Aided by theory, the state-selective formation and breakup of the transient OD+(a1Δ, b1Σ+) is traced, and the most likely dissociation path—OD+: a1Δ or b1Σ+ → A 3Π → X 3Σ− → B 3Σ−—involving a combination of spin–orbit and non-adiabatic charge transfer transitions is determined. The multi-step transition probability of this complex transition sequence in the intermediate fragment ion is directly evaluated as a function of the energy of the transient OD+ above its lowest dissociation limit from the measured ratio of the D+ + O+ + D and competing D+ + D+ + O sequential fragmentation channels, which are measured simultaneously. Our coupled-channel time-dependent dynamics calculations reproduce the general trends of these multi-state relative transition rates toward the three-body fragmentation channels.

4. Compact single-shot soft X-ray photon spectrometer for free-electron laser diagnostics

   Kirk A. Larsen, Kurtis Borne, Razib Obaid, and 13 more authors

   Opt. Express, Oct 2023

   Abs DOI

   The photon spectrum from free-electron laser (FEL) light sources offers valuable information in time-resolved experiments and machine optimization in the spectral and temporal domains. We have developed a compact single-shot photon spectrometer to diagnose soft X-ray spectra. The spectrometer consists of an array of off-axis Fresnel zone plates (FZP) that act as transmission-imaging gratings, a Ce:YAG scintillator, and a microscope objective to image the scintillation target onto a two-dimensional imaging detector. This spectrometer operates in segmented energy ranges which covers tens of electronvolts for each absorption edge associated with several atomic constituents: carbon, nitrogen, oxygen, and neon. The spectrometer’s performance is demonstrated at a repetition rate of 120 Hz, but our detection scheme can be easily extended to 200 kHz spectral collection by employing a fast complementary metal oxide semiconductor (CMOS) line-scan camera to detect the light from the scintillator. This compact photon spectrometer provides an opportunity for monitoring the spectrum downstream of an endstation in a limited space environment with sub-electronvolt energy resolution.

2022

1. Step-by-step state-selective tracking of fragmentation dynamics of water dications by momentum imaging

   Travis Severt, Zachary L. Streeter, Wael Iskandar, and 18 more authors

   Nature Communications, Sep 2022

   Abs DOI

   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 a surprisingly detailed picture of the dynamics. Determining the time evolution and quantum mechanical states involved leads to deeper understanding of molecular dynamics. Here in a combined experimental and theoretical study, we unambiguously separate the sequential breakup via D+\thinspace+\thinspaceOD+ intermediates, from other processes leading to the same D+\thinspace+\thinspaceD+\thinspace+\thinspaceO final products of double ionization of water by a single photon. Moreover, we experimentally identify, separate, and follow step by step, two pathways involving the b\thinspace1Σ+ and a 1∆electronic states of the intermediate OD+ ion. Our classical trajectory calculations on the relevant potential energy surfaces reproduce well the measured data and, combined with the experiment, enable the determination of the internal energy and angular momentum distribution of the OD+ intermediate.

2021

1. Nonequilibrium dissociative dynamics of \mathrmD_2 in two-color, few-photon excitation and ionization

   D. S. Slaughter, F. P. Sturm, Roger Y. Bello, and 10 more authors

   Phys. Rev. Res., Aug 2021

   DOI
2. SILIA: software implementation of a multi-channel, multi-frequency lock-in amplifier for spectroscopy and imaging applications

   Amrut Nadgir, Richard Thurston, Kirk A Larsen, and 3 more authors

   Measurement Science and Technology, Sep 2021

   Abs DOI

   We describe a software implementation of a multi-channel, multi-frequency Lock-in Amplifier (SILIA) to extract modulated signals from noisy data distributed over multiple channels of arbitrary number and size. This software implementation emulates the functionality of a multi-channel, multi-frequency lock-in amplifier in a post-processing step following data acquisition. Unlike most traditional lock-in amplifiers, SILIA can work with any number of input channels and is especially useful to analyze data distributed over many channels. We demonstrate the versatility and performance for extracting weak signals in spectroscopy and fluorescence microscopy. We also discuss more general applications and exhibit a method to automatically estimate error from a lock-in result.

2020

1. Angle-resolved nonresonant two-photon single ionization of argon using 9.3-eV photons produced via high-order harmonic generation

   Kirk A. Larsen, Daniel S. Slaughter, and Thorsten Weber

   Phys. Rev. A, Jun 2020

   DOI
2. Distinguishing resonance symmetries with energy-resolved photoion angular distributions from ion-pair formation in O2 following two-photon absorption of a 9.3 eV femtosecond pulse

   Kirk A. Larsen, Robert R. Lucchese, Daniel S. Slaughter, and 1 more author

   The Journal of Chemical Physics, Jul 2020

   Abs DOI

   We present a combined experimental and theoretical study on the photodissociation dynamics of ion-pair formation in O2 following resonant two-photon absorption of a 9.3 eV femtosecond pulse, where the resulting O+ ions are detected using 3D momentum imaging. Ion-pair formation states of Σg−3 and 3Πg symmetry are accessed through predissociation of optically dark continuum Rydberg states converging to the B Σg−2 ionic state, which are resonantly populated via a mixture of both parallel–parallel and parallel–perpendicular two-photon transitions. This mixture is evident in the angular distribution of the dissociation relative to the light polarization and varies with the kinetic energy release (KER) of the fragmenting ion pair. The KER-dependent photoion angular distribution reveals the underlying two-photon absorption dynamics involved in the ion-pair production mechanism and indicates the existence of two nearly degenerate continuum resonances possessing different symmetries, which can decay by coupling to ion-pair states of the same total symmetry through internal conversion.

3. Photoelectron and fragmentation dynamics of the \mathrmH^++\mathrmH^+ dissociative channel in \mathrmNH_3 following direct single-photon double ionization

   Kirk A. Larsen, Thomas N. Rescigno, Travis Severt, and 18 more authors

   Phys. Rev. Res., Oct 2020

   DOI
4. Mechanisms and dynamics of the NH+2 + H+ and NH+ + H+ + H fragmentation channels upon single-photon double ionization of NH3

   Kirk A Larsen, Thomas N Rescigno, Zachary L Streeter, and 18 more authors

   Journal of Physics B: Atomic, Molecular and Optical Physics, Nov 2020

   Abs DOI

   We present state-selective measurements on the + H+ and NH+ + H+ + H dissociation channels following single-photon double ionization at 61.5 eV of neutral NH3, where the two photoelectrons and two cations are measured in coincidence using 3D momentum imaging. Three dication electronic states are identified to contribute to the + H+ dissociation channel, where the excitation in one of the three states undergoes intersystem crossing prior to dissociation, producing a cold fragment. In contrast, the other two states directly dissociate, producing a ro-vibrationally excited fragment with roughly 1 eV of internal energy. The NH+ + H+ + H channel is fed by direct dissociation from three intermediate dication states, one of which is shared with the + H+ channel. We find evidence of autoionization contributing to each of the double ionization channels. The distributions of the relative emission angle between the two photoelectrons, as well as the relative angle between the recoil axis of the molecular breakup and the polarization vector of the ionizing field, are also presented to provide insight on both the photoionization and photodissociation mechanisms for the different dication states.

5. Role of dipole-forbidden autoionizing resonances in nonresonant one-color two-photon single ionization of \mathrmN_2

   Kirk A. Larsen, Roger Y. Bello, Robert R. Lucchese, and 4 more authors

   Phys. Rev. A, Dec 2020

   DOI

2019

1. Ultrafast photodissociation dynamics and nonadiabatic coupling between excited electronic states of methanol probed by time-resolved photoelectron spectroscopy

   Elio G. Champenois, Loren Greenman, Niranjan Shivaram, and 6 more authors

   The Journal of Chemical Physics, Mar 2019

   Abs DOI

   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 electronic structure calculations. The photoexcitation pump pulse is followed by a delayed 260 nm photoionization probe pulse to produce photoelectrons that are analyzed by velocity map imaging. The yields of mass-resolved ions, measured with similar experimental conditions, are found to exhibit the same time-dependence as specific photoelectron spectral features. Energy-resolved signal onset and decay times are extracted from the measured photoelectron spectra to achieve high temporal resolution, beyond the 20 fs pump and probe pulse durations. When combined with ab initio calculations of selected cuts through the excited state potential energy surfaces, this information allows the dynamics of the transient excited molecule, which exhibits multiple nuclear and electronic degrees of freedom, to be tracked on its intrinsic few-femtosecond time scale. Within 15 fs of photoexcitation, we observe nuclear motion on the initially bound photoexcited 21A″ (S2) electronic state, through a conical intersection with the 11A′ (S3) state, which reveals paths to photodissociation following C–O stretch and C–O–H angle opening.

2. Tracing intermolecular Coulombic decay of carbon-dioxide dimers and oxygen dimers after valence photoionization

   W. Iskandar, A. S. Gatton, B. Gaire, and 17 more authors

   Phys. Rev. A, Apr 2019

   DOI
3. Symmetry breaking in the body-fixed electron emission pattern due to electron-retroaction in the photodissociation of \mathrmH_2^+ and \mathrmD_2^+ close to threshold

   S. Heck, A. Gatton, K. A. Larsen, and 14 more authors

   Phys. Rev. Res., Dec 2019

   DOI

2018

1. Resonance signatures in the body-frame valence photoionization of CF4

   K. A. Larsen, C. S. Trevisan, R. R. Lucchese, and 18 more authors

   Phys. Chem. Chem. Phys., Dec 2018

   Abs DOI

   We present a combined experimental and theoretical investigation of the electron dynamics and body-frame angular dependence of valence photo-single ionization of CF4 and subsequent dissociation into CF3+ and F. Ionization from a valence t2 orbital shows overlapping shape resonances close to threshold that couple to the same total symmetry, leading to striking changes in the photoelectron angular distributions when viewed in the body-frame.

2016

1. VUV and XUV reflectance of optically coated mirrors for selection of high harmonics

   K. A. Larsen, J. P. Cryan, N. Shivaram, and 7 more authors

   Opt. Express, Aug 2016

   Abs DOI

   We report the reflectance,  1° from normal incidence, of six different mirrors as a function of photon energy, using monochromatic vacuum ultraviolet (VUV) and extreme ultraviolet (XUV) radiation with energies between 7.5 eV and 24.5 eV. The mirrors examined included both single and multilayer optical coatings, as well as an uncoated substrate. We discuss the performance of each mirror, paying particular attention to the potential application of suppression and selection of high-order harmonics of a Ti:sapphire laser.