Kirk Larsen
Associate Scientist, SLAC National Accelerator Laboratory
Bio
I am an associate staff scientist in the Laser Science Department of the Linac Coherent Light Source (LCLS) at SLAC National Accelerator Laboratory. I work on developing tunable few-cycle UV light sources using soliton dynamics and resonant dispersive wave emission in hollow core fibers. I am involved in photoinjector research for LCLS-II, focusing on temporal x-ray pulse shaping to support the extension of attosecond capabilities to high repetition rate. I also work on developing plasma based attosecond XUV light sources at FACET-II.
Education & Certifications
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BS, University of Oregon (2014)
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PhD, University of California, Berkeley (2020)
All Publications
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"Beam à la carte": Laser heater shaping for attosecond pulses in a multiplexed x-ray free-electron laser
APPLIED PHYSICS LETTERS
2024; 125 (19)
View details for DOI 10.1063/5.0233468
View details for Web of Science ID 001349444700011
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Quantitative x-ray scattering of free molecules
JOURNAL OF PHYSICS B-ATOMIC MOLECULAR AND OPTICAL PHYSICS
2024; 57 (20)
View details for DOI 10.1088/1361-6455/ad78d0
View details for Web of Science ID 001316206100001
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Attosecond impulsive stimulated X-ray Raman scattering in liquid water.
Science advances
2024; 10 (39): eadp0841
Abstract
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.
View details for DOI 10.1126/sciadv.adp0841
View details for PubMedID 39321305
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Tracking ultrafast non-adiabatic dissociation dynamics of the deuterated water dication molecule.
The Journal of chemical physics
2024; 161 (4)
Abstract
We applied reaction microscopy to elucidate fast non-adiabatic dissociation dynamics of deuterated water molecules after direct photo-double ionization at 61eV 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.
View details for DOI 10.1063/5.0219029
View details for PubMedID 39056387
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Wavelength scaling and multicolor operation of a plasma-driven attosecond x-ray source via harmonic generation
PHYSICAL REVIEW ACCELERATORS AND BEAMS
2024; 27 (7)
View details for DOI 10.1103/PhysRevAccelBeams.27.070701
View details for Web of Science ID 001267443100001
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The Linac Coherent Light Source II photoinjector laser infrastructure
HIGH POWER LASER SCIENCE AND ENGINEERING
2024; 12
View details for DOI 10.1017/hpl.2024.33
View details for Web of Science ID 001318028000001
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Terawatt-scale attosecond X-ray pulses from a cascaded superradiant free-electron laser
NATURE PHOTONICS
2024
View details for DOI 10.1038/s41566-024-01427-w
View details for Web of Science ID 001220935700001
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Experimental demonstration of attosecond pump-probe spectroscopy with an X-ray free-electron laser
NATURE PHOTONICS
2024
View details for DOI 10.1038/s41566-024-01419-w
View details for Web of Science ID 001200371400001
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Attosecond-pump attosecond-probe x-ray spectroscopy of liquid water.
Science (New York, N.Y.)
2024: eadn6059
Abstract
Attosecond-pump/attosecond-probe experiments have long been sought as the most straightforward method to observe electron dynamics in real time. Although numerous successes have been achieved 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 via 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 for two structural motifs in ambient liquid water.
View details for DOI 10.1126/science.adn6059
View details for PubMedID 38359104
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Compact single-shot soft X-ray photon spectrometer for free-electron laser diagnostics
OPTICS EXPRESS
2023; 31 (22): 35822-35834
Abstract
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.
View details for DOI 10.1364/OE.502105
View details for Web of Science ID 001106418000001
View details for PubMedID 38017746
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Efficiency of charge transfer in changing the dissociation dynamics of OD<SUP>+</SUP> transients formed after the photo-fragmentation of D<sub>2</sub>O
JOURNAL OF CHEMICAL PHYSICS
2023; 159 (9)
Abstract
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.
View details for DOI 10.1063/5.0159300
View details for Web of Science ID 001063483100004
View details for PubMedID 37668253
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Strongly coupled intermediate electronic states in one-color two-photon single valence ionization of O2.
The Journal of chemical physics
2023; 158 (2): 024303
Abstract
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 9.3eV 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.
View details for DOI 10.1063/5.0128846
View details for PubMedID 36641397
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Step-by-step state-selective tracking of fragmentation dynamics of water dications by momentum imaging.
Nature communications
2022; 13 (1): 5146
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 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++OD+ intermediates, from other processes leading to the same D++D++O 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 b1Sigma+ and a 1Delta 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.
View details for DOI 10.1038/s41467-022-32836-6
View details for PubMedID 36050308
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Mechanisms and dynamics of the NH2+ + H+ and NH+ + H+ + H fragmentation channels upon single-photon double ionization of NH3
JOURNAL OF PHYSICS B-ATOMIC MOLECULAR AND OPTICAL PHYSICS
2020; 53 (24)
View details for DOI 10.1088/1361-6455/abc3aa
View details for Web of Science ID 000591070400001
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Role of dipole-forbidden autoionizing resonances in nonresonant one-color two-photon single ionization of N-2
PHYSICAL REVIEW A
2020; 102 (6)
View details for DOI 10.1103/PhysRevA.102.063118
View details for Web of Science ID 000601327400009
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Photoelectron and fragmentation dynamics of the H+
PHYSICAL REVIEW RESEARCH
2020; 2 (4)
View details for DOI 10.1103/PhysRevResearch.2.043056
View details for Web of Science ID 000605392100006
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Distinguishing resonance symmetries with energy-resolved photoion angular distributions from ion-pair formation in O-2 following two-photon absorption of a 9.3 eV femtosecond pulse
JOURNAL OF CHEMICAL PHYSICS
2020; 153 (2): 021103
Abstract
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.
View details for DOI 10.1063/5.0013485
View details for Web of Science ID 000553097500001
View details for PubMedID 32668943
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Angle-resolved nonresonant two-photon single ionization of argon using 9.3-eV photons produced via high-order harmonic generation
PHYSICAL REVIEW A
2020; 101 (6)
View details for DOI 10.1103/PhysRevA.101.061402
View details for Web of Science ID 000538335500001
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Symmetry breaking in the body-fixed electron emission pattern due to electron-retroaction in the photodissociation of H-2(+) and D-2(+) close to threshold
PHYSICAL REVIEW RESEARCH
2019; 1 (3)
View details for DOI 10.1103/PhysRevResearch.1.033140
View details for Web of Science ID 000600650500001
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Tracing intermolecular Coulombic decay of carbon-dioxide dimers and oxygen dimers after valence photoionization
PHYSICAL REVIEW A
2019; 99 (4)
View details for DOI 10.1103/PhysRevA.99.043414
View details for Web of Science ID 000464711300006
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Ultrafast photodissociation dynamics and nonadiabatic coupling between excited electronic states of methanol probed by time-resolved photoelectron spectroscopy
JOURNAL OF CHEMICAL PHYSICS
2019; 150 (11)
View details for DOI 10.1063/1.5079549
View details for Web of Science ID 000462014500017
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Ultrafast photodissociation dynamics and nonadiabatic coupling between excited electronic states of methanol probed by time-resolved photoelectron spectroscopy.
The Journal of chemical physics
2019; 150 (11): 114301
Abstract
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.
View details for PubMedID 30902015
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Resonance signatures in the body-frame valence photoionization of CF4
PHYSICAL CHEMISTRY CHEMICAL PHYSICS
2018; 20 (32): 21075-21084
Abstract
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.
View details for DOI 10.1039/c8cp03637c
View details for Web of Science ID 000447367900033
View details for PubMedID 30074041
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VUV and XUV reflectance of optically coated mirrors for selection of high harmonics
OPTICS EXPRESS
2016; 24 (16): 18209-18216
Abstract
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.
View details for DOI 10.1364/OE.24.018209
View details for Web of Science ID 000384716000061
View details for PubMedID 27505785