Xijie Wang is a distinguished scientist and the founding director of SLAC MeV-UED user facility at SLAC National Accelerator Laboratory. Xijie Wang has more than 30 years' experience in accelerator physics, free electron laser, THz, and ultrafast science and technology. Xijie pioneered the idea using mega-electron-volt electrons for ultrafast electron diffraction (MeV-UED) and ultrafast electron microscope (MeV-UEM). Under Wang’s direction, SLAC has become the world leader in ultrafast electron scattering technologies including single-shot, diffuse scattering, micro-diffraction, operando and in-situ, the first ever femto-second gas and liquid phase UED. These technologies have opened new frontiers in ultrafast science and materials in extreme conditions, produced insight into ultrafast structure dynamics of 2-D materials; control of the topological properties of matter; and atomic & molecular movies of complex materials such as perovskite and fundamental chemical processes in gas and liquid phases. He established the first ultrafast electron scattering user facility in the world – SLAC MeV-UED in 2019. Xijie Wang initiated superconducting RF gun R&D program at SLAC, and he led the effort established SRF gun R&D for LCLSII-HE.

Prior to his time at SLAC, Wang spent over 20 years at Brookhaven National Laboratory (BNL), where he led development and operations of the Accelerator Test Facility (ATF) and the Source Development Laboratory (SDL). Wang played a leading role in research on laser accelerators, high-brightness electron beams, X-ray free electron lasers (FEL), RF deflector for LCLS, THz and MeV-UED at BNL. He developed photocathode RF gun injectors that derived the first saturation of both high-gain harmonic generation (HGHG) FEL at BNL’s ATF and Self-amplified spontaneous emission (SASE) FEL at Argonne National Laboratory. Wang and his collaborators carried out a series of pioneering FEL experiments in early 2000s: 2nd to 4th harmonic HGHG, VISA (Visible to Infrared SASE Amplifier) SASE FEL and nonlinear harmonic generation characterization; super radiance FEL, detuning and tapering for FEL efficiency improvement.

Xijie Wang has co-authored over 300 publications, including 8 in Science, 4 in Nature, 8 in Science Advances, 18 in Nature family journals, and over 20 in PRL.

Honors & Awards

  • Particle Accelerator Science and Technology Award, IEEE (2021)
  • Director Award, SLAC (2016)

Education & Certifications

  • BS, Shaanxi Normal University, Physics (1982)
  • PhD, UCLA, Physics (1992)


  • Edbert Sie, Clara Nyby, Das Pemmaraju Xijie Wang, Aaron Lindenberg. "United States Patent 10861995 Fast topological switch using strained weyl semimetals", Leland Stanford Junior University, Dec 8, 2020

All Publications

  • Coupling to octahedral tilts in halide perovskite nanocrystals induces phonon-mediated attractive interactions between excitons. Nature physics Yazdani, N., Bodnarchuk, M. I., Bertolotti, F., Masciocchi, N., Fureraj, I., Guzelturk, B., Cotts, B. L., Zajac, M., Rainò, G., Jansen, M., Boehme, S. C., Yarema, M., Lin, M. F., Kozina, M., Reid, A., Shen, X., Weathersby, S., Wang, X., Vauthey, E., Guagliardi, A., Kovalenko, M. V., Wood, V., Lindenberg, A. M. 2024; 20 (1): 47-53


    Understanding the origin of electron-phonon coupling in lead halide perovskites is key to interpreting and leveraging their optical and electronic properties. Here we show that photoexcitation drives a reduction of the lead-halide-lead bond angles, a result of deformation potential coupling to low-energy optical phonons. We accomplish this by performing femtosecond-resolved, optical-pump-electron-diffraction-probe measurements to quantify the lattice reorganization occurring as a result of photoexcitation in nanocrystals of FAPbBr3. Our results indicate a stronger coupling in FAPbBr3 than CsPbBr3. We attribute the enhanced coupling in FAPbBr3 to its disordered crystal structure, which persists down to cryogenic temperatures. We find the reorganizations induced by each exciton in a multi-excitonic state constructively interfere, giving rise to a coupling strength that scales quadratically with the exciton number. This superlinear scaling induces phonon-mediated attractive interactions between excitations in lead halide perovskites.

    View details for DOI 10.1038/s41567-023-02253-7

    View details for PubMedID 38261834

    View details for PubMedCentralID PMC10791581

  • Multi-objective Bayesian active learning for MeV-ultrafast electron diffraction. Nature communications Ji, F., Edelen, A., Roussel, R., Shen, X., Miskovich, S., Weathersby, S., Luo, D., Mo, M., Kramer, P., Mayes, C., Othman, M. A., Nanni, E., Wang, X., Reid, A., Minitti, M., England, R. J. 2024; 15 (1): 4726


    Ultrafast electron diffraction using MeV energy beams(MeV-UED) has enabled unprecedented scientific opportunities in the study of ultrafast structural dynamics in a variety of gas, liquid and solid state systems. Broad scientific applications usually pose different requirements for electron probe properties. Due to the complex, nonlinear and correlated nature of accelerator systems, electron beam property optimization is a time-taking process and often relies on extensive hand-tuning by experienced human operators. Algorithm based efficient online tuning strategies are highly desired. Here, we demonstrate multi-objective Bayesian active learning for speeding up online beam tuning at the SLAC MeV-UED facility. The multi-objective Bayesian optimization algorithm was used for efficiently searching the parameter space and mapping out the Pareto Fronts which give the trade-offs between key beam properties. Such scheme enables an unprecedented overview of the global behavior of the experimental system and takes a significantly smaller number of measurements compared with traditional methods such as a grid scan. This methodology can be applied in other experimental scenarios that require simultaneously optimizing multiple objectives by explorations in high dimensional, nonlinear and correlated systems.

    View details for DOI 10.1038/s41467-024-48923-9

    View details for PubMedID 38830874

    View details for PubMedCentralID PMC11148007

  • Giant Terahertz Birefringence in an Ultrathin Anisotropic Semimetal. Nano letters Sie, E. J., Othman, M. A., Nyby, C. M., Pemmaraju, D., Garcia, C. A., Wang, Y., Guzelturk, B., Xia, C., Xiao, J., Poletayev, A., Ofori-Okai, B. K., Hoffmann, M. C., Park, S., Shen, X., Yang, J., Li, R., Reid, A. H., Weathersby, S., Muscher, P., Finney, N., Rhodes, D., Balicas, L., Nanni, E., Hone, J., Chueh, W., Devereaux, T. P., Narang, P., Heinz, T. F., Wang, X., Lindenberg, A. M. 2024


    Manipulating the polarization of light at the nanoscale is key to the development of next-generation optoelectronic devices. This is typically done via waveplates using optically anisotropic crystals, with thicknesses on the order of the wavelength. Here, using a novel ultrafast electron-beam-based technique sensitive to transient near fields at THz frequencies, we observe a giant anisotropy in the linear optical response in the semimetal WTe2 and demonstrate that one can tune the THz polarization using a 50 nm thick film, acting as a broadband wave plate with thickness 3 orders of magnitude smaller than the wavelength. The observed circular deflections of the electron beam are consistent with simulations tracking the trajectory of the electron beam in the near field of the THz pulse. This finding offers a promising approach to enable atomically thin THz polarization control using anisotropic semimetals and defines new approaches for characterizing THz near-field optical response at far-subwavelength length scales.

    View details for DOI 10.1021/acs.nanolett.4c00758

    View details for PubMedID 38717626

  • Direct observation of strong momentum-dependent electron-phonon coupling in a metal. Science advances Mo, M., Tamm, A., Metsanurk, E., Chen, Z., Wang, L., Frost, M., Hartley, N. J., Ji, F., Pandolfi, S., Reid, A. H., Sun, P., Shen, X., Wang, Y., Wang, X., Glenzer, S., Correa, A. A. 2024; 10 (11): eadk9051


    Phonon scattering in metals is one of the most fundamental processes in materials science. However, understanding such processes has remained challenging and requires detailed information on interactions between phonons and electrons. We use an ultrafast electron diffuse scattering technique to resolve the nonequilibrium phonon dynamics in femtosecond-laser-excited tungsten in both time and momentum. We determine transient populations of phonon modes which show strong momentum dependence initiated by electron-phonon coupling. For phonons near Brillouin zone border, we observe a transient rise in their population on a timescale of approximately 1 picosecond driven by the strong electron-phonon coupling, followed by a slow decay on a timescale of approximately 8 picosecond governed by the weaker phonon-phonon relaxation process. We find that the exceptional harmonicity of tungsten is needed for isolating the two processes, resulting in long-lived nonequilibrium phonons in a pure metal. Our finding highlights that electron-phonon scattering can be the determinant factor in the phonon thermal transport of metals.

    View details for DOI 10.1126/sciadv.adk9051

    View details for PubMedID 38478610

  • Improved temporal resolution in ultrafast electron diffraction measurements through THz compression and time-stamping. Structural dynamics (Melville, N.Y.) Othman, M. A., Gabriel, A. E., Snively, E. C., Kozina, M. E., Shen, X., Ji, F., Lewis, S., Weathersby, S., Vasireddy, P., Luo, D., Wang, X., Hoffmann, M. C., Nanni, E. A. 2024; 11 (2): 024311


    We present an experimental demonstration of ultrafast electron diffraction (UED) with THz-driven electron bunch compression and time-stamping that enables UED probes with improved temporal resolution. Through THz-driven longitudinal bunch compression, a compression factor of approximately four is achieved. Moreover, the time-of-arrival jitter between the compressed electron bunch and a pump laser pulse is suppressed by a factor of three. Simultaneously, the THz interaction imparts a transverse spatiotemporal correlation on the electron distribution, which we utilize to further enhance the precision of time-resolved UED measurements. We use this technique to probe single-crystal gold nanofilms and reveal transient oscillations in the THz near fields with a temporal resolution down to 50 fs. These oscillations were previously beyond reach in the absence of THz compression and time-stamping.

    View details for DOI 10.1063/4.0000230

    View details for PubMedID 38655563

    View details for PubMedCentralID PMC11037933

  • Monitoring the Evolution of Relative Product Populations at Early Times during a Photochemical Reaction. Journal of the American Chemical Society Figueira Nunes, J. P., Ibele, L. M., Pathak, S., Attar, A. R., Bhattacharyya, S., Boll, R., Borne, K., Centurion, M., Erk, B., Lin, M., Forbes, R. J., Goff, N., Hansen, C. S., Hoffmann, M., Holland, D. M., Ingle, R. A., Luo, D., Muvva, S. B., Reid, A. H., Rouzee, A., Rudenko, A., Saha, S. K., Shen, X., Venkatachalam, A. S., Wang, X., Ware, M. R., Weathersby, S. P., Wilkin, K., Wolf, T. J., Xiong, Y., Yang, J., Ashfold, M. N., Rolles, D., Curchod, B. F. 2024


    Identifying multiple rival reaction products and transient species formed during ultrafast photochemical reactions and determining their time-evolving relative populations are key steps toward understanding and predicting photochemical outcomes. Yet, most contemporary ultrafast studies struggle with clearly identifying and quantifying competing molecular structures/species among the emerging reaction products. Here, we show that mega-electronvolt ultrafast electron diffraction in combination with ab initio molecular dynamics calculations offer a powerful route to determining time-resolved populations of the various isomeric products formed after UV (266 nm) excitation of the five-membered heterocyclic molecule 2(5H)-thiophenone. This strategy provides experimental validation of the predicted high (50%) yield of an episulfide isomer containing a strained three-membered ring within 1 ps of photoexcitation and highlights the rapidity of interconversion between the rival highly vibrationally excited photoproducts in their ground electronic state.

    View details for DOI 10.1021/jacs.3c13046

    View details for PubMedID 38317439

  • Capturing the generation and structural transformations of molecular ions NATURE Heo, J., Kim, D., Segalina, A., Ki, H., Ahn, D., Lee, S., Kim, J., Cha, Y., Lee, K., Yang, J., Nunes, J. F., Wang, X., Ihee, H. 2024; 625 (7996): 710-714


    Molecular ions are ubiquitous and play pivotal roles1-3 in many reactions, particularly in the context of atmospheric and interstellar chemistry4-6. However, their structures and conformational transitions7,8, particularly in the gas phase, are less explored than those of neutral molecules owing to experimental difficulties. A case in point is the halonium ions9-11, whose highly reactive nature and ring strain make them short-lived intermediates that are readily attacked even by weak nucleophiles and thus challenging to isolate or capture before they undergo further reaction. Here we show that mega-electronvolt ultrafast electron diffraction (MeV-UED)12-14, used in conjunction with resonance-enhanced multiphoton ionization, can monitor the formation of 1,3-dibromopropane (DBP) cations and their subsequent structural dynamics forming a halonium ion. We find that the DBP+ cation remains for a substantial duration of 3.6 ps in aptly named 'dark states' that are structurally indistinguishable from the DBP electronic ground state. The structural data, supported by surface-hopping simulations15 and ab initio calculations16, reveal that the cation subsequently decays to iso-DBP+, an unusual intermediate with a four-membered ring containing a loosely bound17,18 bromine atom, and eventually loses the bromine atom and forms a bromonium ion with a three-membered-ring structure19. We anticipate that the approach used here can also be applied to examine the structural dynamics of other molecular ions and thereby deepen our understanding of ion chemistry.

    View details for DOI 10.1038/s41586-023-06909-5

    View details for Web of Science ID 001163662900003

    View details for PubMedID 38200317

    View details for PubMedCentralID PMC10808067

  • Applying Bayesian inference and deterministic anisotropy to retrieve the molecular structure ÷Ψ(<bold>R</bold>)÷<SUP>2</SUP> distribution from gas-phase diffraction experiments COMMUNICATIONS PHYSICS Hegazy, K., Makhija, V., Bucksbaum, P., Corbett, J., Cryan, J., Hartmann, N., Ilchen, M., Jobe, K., Li, R., Makasyuk, I., Shen, X., Wang, X., Weathersby, S., Yang, J., Coffee, R. 2023; 6 (1)
  • Coupling to octahedral tilts in halide perovskite nanocrystals induces phonon-mediated attractive interactions between excitons NATURE PHYSICS Yazdani, N., Bodnarchuk, M. I., Bertolotti, F., Masciocchi, N., Fureraj, I., Guzelturk, B., Cotts, B. L., Zajac, M., Raino, G., Jansen, M., Boehme, S. C., Yarema, M., Lin, M., Kozina, M., Reid, A., Shen, X., Weathersby, S., Wang, X., Vauthey, E., Guagliardi, A., Kovalenko, M. V., Wood, V., Lindenberg, A. M. 2023
  • Femtosecond Electronic and Hydrogen Structural Dynamics in Ammonia Imaged with Ultrafast Electron Diffraction. Physical review letters Champenois, E. G., List, N. H., Ware, M., Britton, M., Bucksbaum, P. H., Cheng, X., Centurion, M., Cryan, J. P., Forbes, R., Gabalski, I., Hegazy, K., Hoffmann, M. C., Howard, A. J., Ji, F., Lin, M. F., Nunes, J. P., Shen, X., Yang, J., Wang, X., Martinez, T. J., Wolf, T. J. 2023; 131 (14): 143001


    Directly imaging structural dynamics involving hydrogen atoms by ultrafast diffraction methods is complicated by their low scattering cross sections. Here we demonstrate that megaelectronvolt ultrafast electron diffraction is sufficiently sensitive to follow hydrogen dynamics in isolated molecules. In a study of the photodissociation of gas phase ammonia, we simultaneously observe signatures of the nuclear and corresponding electronic structure changes resulting from the dissociation dynamics in the time-dependent diffraction. Both assignments are confirmed by ab initio simulations of the photochemical dynamics and the resulting diffraction observable. While the temporal resolution of the experiment is insufficient to resolve the dissociation in time, our results represent an important step towards the observation of proton dynamics in real space and time.

    View details for DOI 10.1103/PhysRevLett.131.143001

    View details for PubMedID 37862660

  • Author Correction: Ultrafast non-radiative dynamics of atomically thin MoSe2. Nature communications Lin, M., Kochat, V., Krishnamoorthy, A., Oftelie, L. B., Weninger, C., Zheng, Q., Zhang, X., Apte, A., Tiwary, C. S., Shen, X., Li, R., Kalia, R., Ajayan, P., Nakano, A., Vashishta, P., Shimojo, F., Wang, X., Fritz, D. M., Bergmann, U. 2023; 14 (1): 4917

    View details for DOI 10.1038/s41467-023-40538-w

    View details for PubMedID 37582925

  • Spin-mediated shear oscillators in a van der Waals antiferromagnet. Nature Zong, A., Zhang, Q., Zhou, F., Su, Y., Hwangbo, K., Shen, X., Jiang, Q., Liu, H., Gage, T. E., Walko, D. A., Kozina, M. E., Luo, D., Reid, A. H., Yang, J., Park, S., Lapidus, S. H., Chu, J. H., Arslan, I., Wang, X., Xiao, D., Xu, X., Gedik, N., Wen, H. 2023


    Understanding how microscopic spin configuration gives rise to exotic properties at the macroscopic length scale has long been pursued in magnetic materials1-5. One seminal example is the Einstein-de Haas effect in ferromagnets1,6,7, in which angular momentum of spins can be converted into mechanical rotation of an entire object. However, for antiferromagnets without net magnetic moment, how spin ordering couples to macroscopic movement remains elusive. Here we observed a seesaw-like rotation of reciprocal lattice peaks of an antiferromagnetic nanolayer film, whose gigahertz structural resonance exhibits more than an order-of-magnitude amplification after cooling below the Néel temperature. Using a suite of ultrafast diffraction and microscopy techniques, we directly visualize this spin-driven rotation in reciprocal space at the nanoscale. This motion corresponds to interlayer shear in real space, in which individual micro-patches of the film behave as coherent oscillators that are phase-locked and shear along the same in-plane axis. Using time-resolved optical polarimetry, we further show that the enhanced mechanical response strongly correlates with ultrafast demagnetization, which releases elastic energy stored in local strain gradients to drive the oscillators. Our work not only offers the first microscopic view of spin-mediated mechanical motion of an antiferromagnet but it also identifies a new route towards realizing high-frequency resonators8,9 up to the millimetre band, so the capability of controlling magnetic states on the ultrafast timescale10-13 can be readily transferred to engineering the mechanical properties of nanodevices.

    View details for DOI 10.1038/s41586-023-06279-y

    View details for PubMedID 37532936

    View details for PubMedCentralID 10156606

  • Verwey transition as evolution from electronic nematicity to trimerons via electron-phonon coupling. Science advances Wang, W., Li, J., Liang, Z., Wu, L., Lozano, P. M., Komarek, A. C., Shen, X., Reid, A. H., Wang, X., Li, Q., Yin, W., Sun, K., Robinson, I. K., Zhu, Y., Dean, M. P., Tao, J. 2023; 9 (23): eadf8220


    Understanding the driving mechanisms behind metal-insulator transitions (MITs) is a critical step toward controlling material's properties. Since the proposal of charge order-induced MIT in magnetite Fe3O4 in 1939 by Verwey, the nature of the charge order and its role in the transition have remained elusive. Recently, a trimeron order was found in the low-temperature structure of Fe3O4; however, the expected transition entropy change in forming trimeron is greater than the observed value, which arises a reexamination of the ground state in the high-temperature phase. Here, we use electron diffraction to unveil that a nematic charge order on particular Fe sites emerges in the high-temperature structure of bulk Fe3O4 and that, upon cooling, a competitive intertwining of charge and lattice orders arouses the Verwey transition. Our findings discover an unconventional type of electronic nematicity in correlated materials and offer innovative insights into the transition mechanism in Fe3O4 via the electron-phonon coupling.

    View details for DOI 10.1126/sciadv.adf8220

    View details for PubMedID 37294769

  • Rehybridization dynamics into the pericyclic minimum of an electrocyclic reaction imaged in real-time. Nature communications Liu, Y., Sanchez, D. M., Ware, M. R., Champenois, E. G., Yang, J., Nunes, J. P., Attar, A., Centurion, M., Cryan, J. P., Forbes, R., Hegazy, K., Hoffmann, M. C., Ji, F., Lin, M., Luo, D., Saha, S. K., Shen, X., Wang, X. J., Martinez, T. J., Wolf, T. J. 2023; 14 (1): 2795


    Electrocyclic reactions are characterized by the concerted formation and cleavage of both sigma and pi bonds through a cyclic structure. This structure is known as a pericyclic transition state for thermal reactions and a pericyclic minimum in the excited state for photochemical reactions. However, the structure of the pericyclic geometry has yet to be observed experimentally. We use a combination of ultrafast electron diffraction and excited state wavepacket simulations to image structural dynamics through the pericyclic minimum of a photochemical electrocyclic ring-opening reaction in the molecule alpha-terpinene. The structural motion into the pericyclic minimum is dominated by rehybridization of two carbon atoms, which is required for the transformation from two to three conjugated pi bonds. The sigma bond dissociation largely happens after internal conversion from the pericyclic minimum to the electronic ground state. These findings may be transferrable to electrocyclic reactions in general.

    View details for DOI 10.1038/s41467-023-38513-6

    View details for PubMedID 37202402

  • Measurement of femtosecond dynamics of ultrafast electron beams through terahertz compression and time-stamping APPLIED PHYSICS LETTERS Othman, M. K., Gabriel, A. E., Snively, E. C., Kozina, M. E., Shen, X., Ji, F., Lewis, S., Weathersby, S., Vasireddy, P., Luo, D., Wang, X., Hoffmann, M. C., Nanni, E. A. 2023; 122 (14)

    View details for DOI 10.1063/5.0134733

    View details for Web of Science ID 000964331000010

  • Understanding and Controlling Photothermal Responses in MXenes. Nano letters Guzelturk, B., Kamysbayev, V., Wang, D., Hu, H., Li, R., King, S. B., Reid, A. H., Lin, M., Wang, X., Walko, D. A., Zhang, X., Lindenberg, A., Talapin, D. V. 2023


    MXenes have the potential for efficient light-to-heat conversion in photothermal applications. To effectively utilize MXenes in such applications, it is important to understand the underlying nonequilibrium processes, including electron-phonon and phonon-phonon couplings. Here, we use transient electron and X-ray diffraction to investigate the heating and cooling of photoexcited MXenes at femtosecond to nanosecond time scales. Our results show extremely strong electron-phonon coupling in Ti3C2-based MXenes, resulting in lattice heating within a few hundred femtoseconds. We also systematically study heat dissipation in MXenes with varying film thicknesses, chemical surface terminations, flake sizes, and annealing conditions. We find that the thermal boundary conductance (TBC) governs the thermal relaxation in films thinner than the optical penetration depth. We achieve a 2-fold enhancement of the TBC, reaching 20 MW m-2 K-1, by controlling the flake size or chemical surface termination, which is promising for engineering heat dissipation in photothermal and thermoelectric applications of the MXenes.

    View details for DOI 10.1021/acs.nanolett.2c05001

    View details for PubMedID 36917456

  • Ultrafast Optomechanical Strain in Layered GeS. Nano letters Luo, D., Zhang, B., Sie, E. J., Nyby, C. M., Fan, Q., Shen, X., Reid, A. H., Hoffmann, M. C., Weathersby, S., Wen, J., Qian, X., Wang, X., Lindenberg, A. M. 2023


    Strong coupling between light and mechanical strain forms the foundation for next-generation optical micro- and nano-electromechanical systems. Such optomechanical responses in two-dimensional materials present novel types of functionalities arising from the weak van der Waals bond between atomic layers. Here, by using structure-sensitive megaelectronvolt ultrafast electron diffraction, we report the experimental observation of optically driven ultrafast in-plane strain in the layered group IV monochalcogenide germanium sulfide (GeS). Surprisingly, the photoinduced structural deformation exhibits strain amplitudes of order 0.1% with a 10 ps fast response time and a significant in-plane anisotropy between zigzag and armchair crystallographic directions. Rather than arising due to heating, experimental and theoretical investigations suggest deformation potentials caused by electronic density redistribution and converse piezoelectric effects generated by photoinduced electric fields are the dominant contributors to the observed dynamic anisotropic strains. Our observations define new avenues for ultrafast optomechanical control and strain engineering within functional devices.

    View details for DOI 10.1021/acs.nanolett.2c05048

    View details for PubMedID 36898060

  • Ultrafast relaxation of lattice distortion in two-dimensional perovskites NATURE PHYSICS Zhang, H., Li, W., Essman, J., Quarti, C., Metcalf, I., Chiang, W., Sidhik, S., Hou, J., Fehr, A., Attar, A., Lin, M., Britz, A., Shen, X., Link, S., Wang, X., Bergmann, U., Kanatzidis, M. G., Katan, C., Even, J., Blancon, J., Mohite, A. D. 2023
  • Bidirectional phonon emission in two-dimensional heterostructures triggered by ultrafast charge transfer. Nature nanotechnology Sood, A., Haber, J. B., Carlström, J., Peterson, E. A., Barre, E., Georgaras, J. D., Reid, A. H., Shen, X., Zajac, M. E., Regan, E. C., Yang, J., Taniguchi, T., Watanabe, K., Wang, F., Wang, X., Neaton, J. B., Heinz, T. F., Lindenberg, A. M., da Jornada, F. H., Raja, A. 2022


    Photoinduced charge transfer in van der Waals heterostructures occurs on the 100 fs timescale despite weak interlayer coupling and momentum mismatch. However, little is understood about the microscopic mechanism behind this ultrafast process and the role of the lattice in mediating it. Here, using femtosecond electron diffraction, we directly visualize lattice dynamics in photoexcited heterostructures of WSe2/WS2 monolayers. Following the selective excitation of WSe2, we measure the concurrent heating of both WSe2 and WS2 on a picosecond timescale-an observation that is not explained by phonon transport across the interface. Using first-principles calculations, we identify a fast channel involving an electronic state hybridized across the heterostructure, enabling phonon-assisted interlayer transfer of photoexcited electrons. Phonons are emitted in both layers on the femtosecond timescale via this channel, consistent with the simultaneous lattice heating observed experimentally. Taken together, our work indicates strong electron-phonon coupling via layer-hybridized electronic states-a novel route to control energy transport across atomic junctions.

    View details for DOI 10.1038/s41565-022-01253-7

    View details for PubMedID 36543882

  • Light-Driven Ultrafast Polarization Manipulation in a Relaxor Ferroelectric. Nano letters Park, S., Wang, B., Yang, T., Kim, J., Saremi, S., Zhao, W., Guzelturk, B., Sood, A., Nyby, C., Zajac, M., Shen, X., Kozina, M., Reid, A. H., Weathersby, S., Wang, X., Martin, L. W., Chen, L. Q., Lindenberg, A. M. 2022


    Relaxor ferroelectrics have been intensely studied for decades based on their unique electromechanical responses which arise from local structural heterogeneity involving polar nanoregions or domains. Here, we report first studies of the ultrafast dynamics and reconfigurability of the polarization in freestanding films of the prototypical relaxor 0.68PbMg1/3Nb2/3O3-0.32PbTiO3 (PMN-0.32PT) by probing its atomic-scale response via femtosecond-resolution, electron-scattering approaches. By combining these structural measurements with dynamic phase-field simulations, we show that femtosecond light pulses drive a change in both the magnitude and direction of the polarization vector within polar nanodomains on few-picosecond time scales. This study defines new opportunities for dynamic reconfigurable control of the polarization in nanoscale relaxor ferroelectrics.

    View details for DOI 10.1021/acs.nanolett.2c02706

    View details for PubMedID 36450036

  • Panoramic Mapping of Phonon Transport from Ultrafast Electron Diffraction and Scientific Machine Learning ADVANCED MATERIALS Chen, Z., Shen, X., Andrejevic, N., Liu, T., Luo, D., Nguyen, T., Drucker, N. C., Kozina, M. E., Song, Q., Hua, C., Chen, G., Wang, X., Kong, J., Li, M. 2022: e2206997


    One central challenge in understanding phonon thermal transport is a lack of experimental tools to investigate frequency-resolved phonon transport. Although recent advances in computation lead to frequency-resolved information, it is hindered by unknown defects in bulk regions and at interfaces. Here, a framework that can uncover microscopic phonon transport information in heterostructures is presented, integrating state-of-the-art ultrafast electron diffraction (UED) with advanced scientific machine learning (SciML). Taking advantage of the dual temporal and reciprocal-space resolution in UED, and the ability of SciML to solve inverse problems involving O ( 10 3 ) $\mathcal{O}({10^3})$ coupled Boltzmann transport equations, the frequency-dependent interfacial transmittance and frequency-dependent relaxation times of the heterostructure from the diffraction patterns are reliably recovered. The framework is applied to experimental Au/Si UED data, and a transport pattern beyond the diffuse mismatch model is revealed, which further enables a direct reconstruction of real-space, real-time, frequency-resolved phonon dynamics across the interface. The work provides a new pathway to probe interfacial phonon transport mechanisms with unprecedented details.

    View details for DOI 10.1002/adma.202206997

    View details for Web of Science ID 000892853800001

    View details for PubMedID 36440651

  • Large Exchange Coupling Between Localized Spins and Topological Bands in Magnetic Topological Insulator MnBi2 Te4. Advanced materials (Deerfield Beach, Fla.) Padmanabhan, H., Stoica, V. A., Kim, P. K., Poore, M., Yang, T., Shen, X., Reid, A. H., Lin, M., Park, S., Yang, J., Hugo Wang, H., Koocher, N. Z., Puggioni, D., Georgescu, A. B., Min, L., Lee, S. H., Mao, Z., Rondinelli, J. M., Lindenberg, A. M., Chen, L., Wang, X., Averitt, R. D., Freeland, J. W., Gopalan, V. 2022: e2202841


    Magnetism in topological materials creates phases exhibiting quantized transport phenomena with potential technological applications. The emergence of such phases relies on strong interaction between localized spins and the topological bands, and the consequent formation of an exchange gap. However, this remains experimentally unquantified in intrinsic magnetic topological materials. Here, this interaction is quantified in MnBi2 Te4 , an intrinsic antiferromagnetic topological insulator. To achieve this, a multimodal ultrafast approach is employed to interrogate optically induced nonequilibrium spin dynamics. Momentum-resolved ultrafast electron scattering and magneto-optic measurements show that Bi-Te p-like states comprising the bulk topological bands demagnetize via electron-phonon scattering at picosecond timescales. Localized Mn 3d spins, probed by ultrafast resonant X-ray scattering, are found to disorder concurrently with the p-like spins, despite being energetically decoupled from the optical excitation. These results, together with atomistic simulations, reveal that the exchange coupling between localized spins and the bulk topological bands is at least 100 times larger than the primary superexchange interaction, implying an optimal exchange gap of at least 25 meV in the topological surface states. By directly quantifying this exchange coupling, the study validates the materials-by-design strategy of utilizing localized magnetic order to create and manipulate magnetic topological phases, spanning static to ultrafast timescales. This article is protected by copyright. All rights reserved.

    View details for DOI 10.1002/adma.202202841

    View details for PubMedID 36189841

  • Interlayer magnetophononic coupling in MnBi2Te4. Nature communications Padmanabhan, H., Poore, M., Kim, P. K., Koocher, N. Z., Stoica, V. A., Puggioni, D., Hugo Wang, H., Shen, X., Reid, A. H., Gu, M., Wetherington, M., Lee, S. H., Schaller, R. D., Mao, Z., Lindenberg, A. M., Wang, X., Rondinelli, J. M., Averitt, R. D., Gopalan, V. 2022; 13 (1): 1929


    The emergence of magnetism in quantum materials creates a platform to realize spin-based applications in spintronics, magnetic memory, and quantum information science. A key to unlocking new functionalities in these materials is the discovery of tunable coupling between spins and other microscopic degrees of freedom. We present evidence for interlayer magnetophononic coupling in the layered magnetic topological insulator MnBi2Te4. Employing magneto-Raman spectroscopy, we observe anomalies in phonon scattering intensities across magnetic field-driven phase transitions, despite the absence of discernible static structural changes. This behavior is a consequence of a magnetophononic wave-mixing process that allows for the excitation of zone-boundary phonons that are otherwise 'forbidden' by momentum conservation. Our microscopic model based on density functional theory calculations reveals that this phenomenon can be attributed to phonons modulating the interlayer exchange coupling. Moreover, signatures of magnetophononic coupling are also observed in the time domain through the ultrafast excitation and detection of coherent phonons across magnetic transitions. In light of the intimate connection between magnetism and topology in MnBi2Te4, the magnetophononic coupling represents an important step towards coherent on-demand manipulation of magnetic topological phases.

    View details for DOI 10.1038/s41467-022-29545-5

    View details for PubMedID 35396393

  • Nonequilibrium sub-10 nm spin-wave soliton formation in FePt nanoparticles SCIENCE ADVANCES Turenne, D., Yaroslavtsev, A., Wang, X., Unikandanuni, V., Vaskivskyi, I., Schneider, M., Jal, E., Carley, R., Mercurio, G., Gort, R., Agarwal, N., Van Kuiken, B., Mercadier, L., Schlappa, J., Le Guyader, L., Gerasimova, N., Teichmann, M., Lomidze, D., Castoldi, A., Potorochin, D., Mukkattukavil, D., Brock, J., Hagstrom, N., Reid, A. H., Shen, X., Wang, X. J., Maldonado, P., Kvashnin, Y., Carva, K., Wang, J., Takahashi, Y. K., Fullerton, E. E., Eisebitt, S., Oppeneer, P. M., Molodtsov, S., Scherz, A., Bonetti, S., Iacocca, E., Durr, H. A. 2022; 8 (13): eabn0523


    Magnetic nanoparticles such as FePt in the L10 phase are the bedrock of our current data storage technology. As the grains become smaller to keep up with technological demands, the superparamagnetic limit calls for materials with higher magnetocrystalline anisotropy. This, in turn, reduces the magnetic exchange length to just a few nanometers, enabling magnetic structures to be induced within the nanoparticles. Here, we describe the existence of spin-wave solitons, dynamic localized bound states of spin-wave excitations, in FePt nanoparticles. We show with time-resolved x-ray diffraction and micromagnetic modeling that spin-wave solitons of sub-10 nm sizes form out of the demagnetized state following femtosecond laser excitation. The measured soliton spin precession frequency of 0.1 THz positions this system as a platform to develop novel miniature devices.

    View details for DOI 10.1126/sciadv.abn0523

    View details for Web of Science ID 000778886800029

    View details for PubMedID 35363518

  • Sub-micron thick liquid sheets produced by isotropically etched glass nozzles. Lab on a chip Crissman, C. J., Mo, M., Chen, Z., Yang, J., Huyke, D. A., Glenzer, S. H., Ledbetter, K., F Nunes, J. P., Ng, M. L., Wang, H., Shen, X., Wang, X., DePonte, D. P. 2022


    We report on the design and testing of glass nozzles used to produce liquid sheets. The sheet nozzles use a single converging channel chemically etched into glass wafers by standard lithographic methods. Operation in ambient air and vacuum was demonstrated. The measured sheet thickness ranges over one order of magnitude with the smallest thickness of 250 nm and the largest of 2.5 mum. Sheet thickness was shown to be independent of liquid flow rate, and dependent on the nozzle outlet area. Sheet surface roughness was dependent on nozzle surface finish and was on the order of 10 nm for polished nozzles. Electron transmission data is presented for various sheet thicknesses near the MeV mean free path and the charge pair distribution function for D2O is determined from electron scattering data.

    View details for DOI 10.1039/d1lc00757b

    View details for PubMedID 35234235

  • Ultrafast visualization of incipient plasticity in dynamically compressed matter. Nature communications Mo, M., Tang, M., Chen, Z., Peterson, J. R., Shen, X., Baldwin, J. K., Frost, M., Kozina, M., Reid, A., Wang, Y., E, J., Descamps, A., Ofori-Okai, B. K., Li, R., Luo, S., Wang, X., Glenzer, S. 2022; 13 (1): 1055


    Plasticity is ubiquitous and plays a critical role in material deformation and damage; it inherently involves the atomistic length scale and picosecond time scale. A fundamental understanding of the elastic-plastic deformation transition, in particular, incipient plasticity, has been a grand challenge in high-pressure and high-strain-rate environments, impeded largely by experimental limitations on spatial and temporal resolution. Here, we report femtosecond MeV electron diffraction measurements visualizing the three-dimensional (3D) response of single-crystal aluminum to the ultrafast laser-induced compression. We capture lattice transitioning from a purely elastic to a plastically relaxed state within 5 ps, after reaching an elastic limit of~25 GPa. Our results allow the direct determination of dislocation nucleation and transport that constitute the underlying defect kinetics of incipient plasticity. Large-scale molecular dynamics simulations show good agreement with the experiment and provide an atomic-level description of the dislocation-mediated plasticity.

    View details for DOI 10.1038/s41467-022-28684-z

    View details for PubMedID 35217665

  • Unconventional Hysteretic Transition in a Charge Density Wave. Physical review letters Lv, B. Q., Zong, A., Wu, D., Rozhkov, A. V., Fine, B. V., Chen, S. D., Hashimoto, M., Lu, D. H., Li, M., Huang, Y. B., Ruff, J. P., Walko, D. A., Chen, Z. H., Hwang, I., Su, Y., Shen, X., Wang, X., Han, F., Po, H. C., Wang, Y., Jarillo-Herrero, P., Wang, X., Zhou, H., Sun, C. J., Wen, H., Shen, Z. X., Wang, N. L., Gedik, N. 2022; 128 (3): 036401


    Hysteresis underlies a large number of phase transitions in solids, giving rise to exotic metastable states that are otherwise inaccessible. Here, we report an unconventional hysteretic transition in a quasi-2D material, EuTe_{4}. By combining transport, photoemission, diffraction, and x-ray absorption measurements, we observe that the hysteresis loop has a temperature width of more than 400 K, setting a record among crystalline solids. The transition has an origin distinct from known mechanisms, lying entirely within the incommensurate charge density wave (CDW) phase of EuTe_{4} with no change in the CDW modulation periodicity. We interpret the hysteresis as an unusual switching of the relative CDW phases in different layers, a phenomenon unique to quasi-2D compounds that is not present in either purely 2D or strongly coupled 3D systems. Our findings challenge the established theories on metastable states in density wave systems, pushing the boundary of understanding hysteretic transitions in a broken-symmetry state.

    View details for DOI 10.1103/PhysRevLett.128.036401

    View details for PubMedID 35119886

  • Role of Equilibrium Fluctuations in Light-Induced Order PHYSICAL REVIEW LETTERS Zong, A., Dolgirev, P. E., Kogar, A., Su, Y., Shen, X., Straquadine, J. W., Wang, X., Luo, D., Kozina, M. E., Reid, A. H., Li, R., Yang, J., Weathersby, S. P., Park, S., Sie, E. J., Jarillo-Herrero, P., Fisher, I. R., Wang, X., Demler, E., Gedik, N. 2021; 127 (22)
  • Effect of lattice excitations on transient near-edge x-ray absorption spectroscopy PHYSICAL REVIEW B Rothenbach, N., Gruner, M. E., Ollefs, K., Schmitz-Antoniak, C., Salamon, S., Zhou, P., Li, R., Mo, M., Park, S., Shen, X., Weathersby, S., Yang, J., Wang, X. J., Sipr, O., Ebert, H., Sokolowski-Tinten, K., Pentcheva, R., Bovensiepen, U., Eschenlohr, A., Wende, H. 2021; 104 (14)
  • Imaging the short-lived hydroxyl-hydronium pair in ionized liquid water. Science (New York, N.Y.) Lin, M., Singh, N., Liang, S., Mo, M., Nunes, J. P., Ledbetter, K., Yang, J., Kozina, M., Weathersby, S., Shen, X., Cordones, A. A., Wolf, T. J., Pemmaraju, C. D., Ihme, M., Wang, X. J. 2021; 374 (6563): 92-95


    [Figure: see text].

    View details for DOI 10.1126/science.abg3091

    View details for PubMedID 34591617

  • Twist-Angle-Dependent Ultrafast Charge Transfer in MoS2-Graphene van der Waals Heterostructures. Nano letters Luo, D., Tang, J., Shen, X., Ji, F., Yang, J., Weathersby, S., Kozina, M. E., Chen, Z., Xiao, J., Ye, Y., Cao, T., Zhang, G., Wang, X., Lindenberg, A. M. 2021


    Vertically stacked transition metal dichalcogenide-graphene heterostructures provide a platform for novel optoelectronic applications with high photoresponse speeds. Photoinduced nonequilibrium carrier and lattice dynamics in such heterostructures underlie these applications but have not been understood. In particular, the dependence of these photoresponses on the twist angle, a key tuning parameter, remains elusive. Here, using ultrafast electron diffraction, we report the simultaneous visualization of charge transfer and electron-phonon coupling in MoS2-graphene heterostructures with different stacking configurations. We find that the charge transfer timescale from MoS2 to graphene varies strongly with twist angle, becoming faster for smaller twist angles, and show that the relaxation timescale is significantly shorter in a heterostructure as compared to a monolayer. These findings illustrate that twist angle constitutes an additional tuning knob for interlayer charge transfer in heterobilayers and deepen our understanding of fundamental photophysical processes in heterostructures, of importance for future applications in optoelectronics and light harvesting.

    View details for DOI 10.1021/acs.nanolett.1c02356

    View details for PubMedID 34529439

  • Fast attenuation of high-frequency acoustic waves in bicontinuous nanoporous gold APPLIED PHYSICS LETTERS Zheng, Q., Tian, Y., Shen, X., Sokolowski-Tinten, K., Li, R. K., Chen, Z., Mo, M. Z., Wang, Z. L., Liu, P., Fujita, T., Weathersby, S. P., Yang, J., Wang, X. J., Chen, M. W. 2021; 119 (6)

    View details for DOI 10.1063/5.0055391

    View details for Web of Science ID 000683519300015

  • Direct observation of ultrafast hydrogen bond strengthening in liquid water. Nature Yang, J., Dettori, R., Nunes, J. P., List, N. H., Biasin, E., Centurion, M., Chen, Z., Cordones, A. A., Deponte, D. P., Heinz, T. F., Kozina, M. E., Ledbetter, K., Lin, M., Lindenberg, A. M., Mo, M., Nilsson, A., Shen, X., Wolf, T. J., Donadio, D., Gaffney, K. J., Martinez, T. J., Wang, X. 2021; 596 (7873): 531-535


    Water is one of the most important, yet least understood, liquids in nature. Many anomalous properties of liquid water originate from its well-connected hydrogen bond network1, including unusually efficient vibrational energy redistribution and relaxation2. An accurate description of the ultrafast vibrational motion of water molecules is essential for understanding the nature of hydrogen bonds and many solution-phase chemical reactions. Most existing knowledge of vibrational relaxation in water is built upon ultrafast spectroscopy experiments2-7. However, these experiments cannot directly resolve the motion of the atomic positions and require difficult translation of spectral dynamics into hydrogen bond dynamics. Here, we measure the ultrafast structural response to the excitation of the OH stretching vibration in liquid water with femtosecond temporal and atomic spatial resolution using liquid ultrafast electron scattering. We observed a transient hydrogen bond contraction of roughly 0.04A on a timescale of 80 femtoseconds, followed by a thermalization on a timescale of approximately 1 picosecond. Molecular dynamics simulations reveal the need to treat the distribution of the shared proton in the hydrogen bond quantum mechanically to capture the structural dynamics on femtosecond timescales. Our experiment and simulations unveil the intermolecular character of the water vibration preceding the relaxation of the OH stretch.

    View details for DOI 10.1038/s41586-021-03793-9

    View details for PubMedID 34433948

  • Frontier nonequilibrium materials science enabled by ultrafast electron methods MRS BULLETIN Siwick, B. J., Arslan, I., Wang, X. 2021; 46 (8): 688-693
  • Highly Efficient Uniaxial In-Plane Stretching of a 2D Material via Ion Insertion. Advanced materials (Deerfield Beach, Fla.) Muscher, P. K., Rehn, D. A., Sood, A., Lim, K., Luo, D., Shen, X., Zajac, M., Lu, F., Mehta, A., Li, Y., Wang, X., Reed, E. J., Chueh, W. C., Lindenberg, A. M. 2021: e2101875


    On-chip dynamic strain engineering requires efficient micro-actuators that can generate large in-plane strains. Inorganic electrochemical actuators are unique in that they are driven by low voltages (1V) and produce considerable strains (1%). However, actuation speed and efficiency are limited by mass transport of ions. Minimizing the number of ions required to actuate is thus key to enabling useful "straintronic" devices. Here, it is shown that the electrochemical intercalation of exceptionally few lithium ions into WTe2 causes large anisotropic in-plane strain: 5% in one in-plane direction and 0.1% in the other. This efficient stretching of the 2D WTe2 layers contrasts to intercalation-induced strains in related materials which are predominantly in the out-of-plane direction. The unusual actuation of Lix WTe2 is linked to the formation of a newly discovered crystallographic phase, referred to as Td', with an exotic atomic arrangement. On-chip low-voltage (<0.2V) control is demonstrated over the transition to the novel phase and its composition. Within the Td'-Li0.5- delta WTe2 phase, a uniaxial in-plane strain of 1.4% is achieved with a change of delta of only 0.075. This makes the in-plane chemical expansion coefficient of Td'-Li0.5-delta WTe2 far greater than of any other single-phase material, enabling fast and efficient planar electrochemical actuation.

    View details for DOI 10.1002/adma.202101875

    View details for PubMedID 34331368

  • Universal phase dynamics in VO2 switches revealed by ultrafast operando diffraction SCIENCE Sood, A., Shen, X., Shi, Y., Kumar, S., Park, S., Zajac, M., Sun, Y., Chen, L., Ramanathan, S., Wang, X., Chueh, W. C., Lindenberg, A. M. 2021; 373 (6552): 352-+
  • Dynamic lattice distortions driven by surface trapping in semiconductor nanocrystals. Nature communications Guzelturk, B., Cotts, B. L., Jasrasaria, D., Philbin, J. P., Hanifi, D. A., Koscher, B. A., Balan, A. D., Curling, E., Zajac, M., Park, S., Yazdani, N., Nyby, C., Kamysbayev, V., Fischer, S., Nett, Z., Shen, X., Kozina, M. E., Lin, M., Reid, A. H., Weathersby, S. P., Schaller, R. D., Wood, V., Wang, X., Dionne, J. A., Talapin, D. V., Alivisatos, A. P., Salleo, A., Rabani, E., Lindenberg, A. M. 2021; 12 (1): 1860


    Nonradiative processes limit optoelectronic functionality of nanocrystals and curb their device performance. Nevertheless, the dynamic structural origins of nonradiative relaxations in such materials are not understood. Here, femtosecond electron diffraction measurements corroborated by atomistic simulations uncover transient lattice deformations accompanying radiationless electronic processes in colloidal semiconductor nanocrystals. Investigation of the excitation energy dependence in a core/shell system shows that hot carriers created by a photon energy considerably larger than the bandgap induce structural distortions at nanocrystal surfaces on few picosecond timescales associated with the localization of trapped holes. On the other hand, carriers created by a photon energy close to the bandgap of the core in the same system result in transient lattice heating that occurs on a much longer 200 picosecond timescale, dominated by an Auger heating mechanism. Elucidation of the structural deformations associated with the surface trapping of hot holes provides atomic-scale insights into the mechanisms deteriorating optoelectronic performance and a pathway towards minimizing these losses in nanocrystal devices.

    View details for DOI 10.1038/s41467-021-22116-0

    View details for PubMedID 33767138

  • Conformer-specific photochemistry imaged in real space and time. Science (New York, N.Y.) Champenois, E. G., Sanchez, D. M., Yang, J., Figueira Nunes, J. P., Attar, A., Centurion, M., Forbes, R., Gühr, M., Hegazy, K., Ji, F., Saha, S. K., Liu, Y., Lin, M. F., Luo, D., Moore, B., Shen, X., Ware, M. R., Wang, X. J., Martínez, T. J., Wolf, T. J. 2021; 374 (6564): 178-182


    [Figure: see text].

    View details for DOI 10.1126/science.abk3132

    View details for PubMedID 34618569

  • Structure retrieval in liquid-phase electron scattering. Physical chemistry chemical physics : PCCP Yang, J., Nunes, J. P., Ledbetter, K., Biasin, E., Centurion, M., Chen, Z., Cordones, A. A., Crissman, C., Deponte, D. P., Glenzer, S. H., Lin, M., Mo, M., Rankine, C. D., Shen, X., Wolf, T. J., Wang, X. 2020


    Electron scattering on liquid samples has been enabled recently by the development of ultrathin liquid sheet technologies. The data treatment of liquid-phase electron scattering has been mostly reliant on methodologies developed for gas electron diffraction, in which theoretical inputs and empirical fittings are often needed to account for the atomic form factor and remove the inelastic scattering background. In this work, we present an alternative data treatment method that is able to retrieve the radial distribution of all the charged particle pairs without the need of either theoretical inputs or empirical fittings. The merits of this new method are illustrated through the retrieval of real-space molecular structure from experimental electron scattering patterns of liquid water, carbon tetrachloride, chloroform, and dichloromethane.

    View details for DOI 10.1039/d0cp06045c

    View details for PubMedID 33367391

  • Photoinduced Dirac semimetal in ZrTe5 NPJ QUANTUM MATERIALS Konstantinova, T., Wu, L., Yin, W., Tao, J., Gu, G. D., Wang, X. J., Yang, J., Zaliznyak, I. A., Zhu, Y. 2020; 5 (1)
  • Photodissociation of aqueous I3- observed with liquid-phase ultrafast mega-electronvolt electron diffraction Structural Dynamics Ledbetter, K., et al 2020; 21: 10


    Developing femtosecond resolution methods for directly observing structural dynamics is critical to understanding complex photochemical reaction mechanisms in solution. We have used two recent developments, ultrafast mega-electron-volt electron sources and vacuum compatible sub-micron thick liquid sheet jets, to enable liquid-phase ultrafast electron diffraction (LUED). We have demonstrated the viability of LUED by investigating the photodissociation of tri-iodide initiated with a 400 nm laser pulse. This has enabled the average speed of the bond expansion to be measured during the first 750 fs of dissociation and the geminate recombination to be directly captured on the picosecond time scale.

    View details for DOI 10.1063/4.0000051

    View details for PubMedCentralID PMC7771998

  • Ultrafast formation of a transient two-dimensional diamondlike structure in twisted bilayer graphene PHYSICAL REVIEW B Luo, D., Hui, D., Wen, B., Li, R., Yang, J., Shen, X., Reid, A., Weathersby, S., Kozina, M. E., Park, S., Ren, Y., Loeffler, T. D., Sankaranarayanan, S. S., Chan, M. Y., Wang, X., Tian, J., Arslan, I., Wang, X., Rajh, T., Wen, J. 2020; 102 (15)
  • Synthesis of Macroscopic Single Crystals of Ge2Sb2Te5 via Single-Shot Femtosecond Optical Excitation CRYSTAL GROWTH & DESIGN Zajac, M., Sood, A., Kim, T. R., Mo, M., Kozina, M., Park, S., Shen, X., Guzelturk, B., Lin, M., Yang, J., Weathersby, S., Wang, X., Lindenberg, A. M. 2020; 20 (10): 6660–67
  • Coherent Lattice Wobbling and Out-of-Phase Intensity Oscillations of Friedel Pairs Observed by Ultrafast Electron Diffraction ACS NANO Qian, Q., Shen, X., Luo, D., Jia, L., Kozina, M., Li, R., Lin, M., Reid, A. H., Weathersby, S., Park, S., Yang, J., Zhou, Y., Zhang, K., Wang, X., Huang, S. 2020; 14 (7): 8449-8458


    The inspection of Friedel's law in ultrafast electron diffraction (UED) is important to gain a comprehensive understanding of material atomic structure and its dynamic response. Here, monoclinic gallium telluride (GaTe), as a low-symmetry, layered crystal in contrast to many other 2D materials, is investigated by mega-electronvolt UED. Strong out-of-phase oscillations of Bragg peak intensities are observed for Friedel pairs, which does not obey Friedel's law. As evidenced by the preserved mirror symmetry and supported by both kinematic and dynamic scattering simulations, the intensity oscillations are provoked by the lowest-order longitudinal acoustic breathing phonon. Our results provide a generalized understanding of Friedel's law in UED and demonstrate that by designed misalignment of surface normal and primitive lattice vectors, coherent lattice wobbling and effective shear strain can be generated in crystal films by laser pulse excitation, which is otherwise hard to achieve and can be further utilized to dynamically tune and switch material properties.

    View details for DOI 10.1021/acsnano.0c02643

    View details for Web of Science ID 000557762800067

    View details for PubMedID 32538617

  • Spectroscopic and Structural Probing of Excited-State Molecular Dynamics with Time-Resolved Photoelectron Spectroscopy and Ultrafast Electron Diffraction PHYSICAL REVIEW X Liu, Y., Horton, S. L., Yang, J., Nunes, J. F., Shen, X., Wolfe, T. A., Forbes, R., Cheng, C., Moore, B., Centurion, M., Hegazy, K., Li, R., Lin, M., Stolow, A., Hockett, P., Rozgonyi, T., Marquetande, P., Wang, X., Weinacht, T. 2020; 10 (2)
  • Concurrent probing of electron-lattice dephasing induced by photoexcitation in 1T-TaSeTe using ultrafast electron diffraction PHYSICAL REVIEW B Li, J., Li, J., Sun, K., Wu, L., Li, R., Yang, J., Shen, X., Wang, X., Luo, H., Cava, R. J., Robinson, I. K., Jin, X., Yin, W., Zhu, Y., Tao, J. 2020; 101 (10)
  • Tracking the ultrafast nonequilibrium energy flow between electronic and lattice degrees of freedom in crystalline nickel PHYSICAL REVIEW B Maldonado, P., Chase, T., Reid, A. H., Shen, X., Li, R. K., Carva, K., Payer, T., von Hoegen, M., Sokolowski-Tinten, K., Wang, X. J., Oppeneer, P. M., Durr, H. A. 2020; 101 (10)
  • Liquid-phase mega-electron-volt ultrafast electron diffraction STRUCTURAL DYNAMICS-US Nunes, J. F., Ledbetter, K., Lin, M., Kozina, M., DePonte, D. P., Biasin, E., Centurion, M., Crissman, C. J., Dunning, M., Guillet, S., Jobe, K., Liu, Y., Mo, M., Shen, X., Sublett, R., Weathersby, S., Yoneda, C., Wolf, T. A., Yang, J., Cordones, A. A., Wang, X. J. 2020; 7 (2): 024301


    The conversion of light into usable chemical and mechanical energy is pivotal to several biological and chemical processes, many of which occur in solution. To understand the structure-function relationships mediating these processes, a technique with high spatial and temporal resolutions is required. Here, we report on the design and commissioning of a liquid-phase mega-electron-volt (MeV) ultrafast electron diffraction instrument for the study of structural dynamics in solution. Limitations posed by the shallow penetration depth of electrons and the resulting information loss due to multiple scattering and the technical challenge of delivering liquids to vacuum were overcome through the use of MeV electrons and a gas-accelerated thin liquid sheet jet. To demonstrate the capabilities of this instrument, the structure of water and its network were resolved up to the 3 rd hydration shell with a spatial resolution of 0.6 Å; preliminary time-resolved experiments demonstrated a temporal resolution of 200 fs.

    View details for DOI 10.1063/1.5144518

    View details for Web of Science ID 000531214100001

    View details for PubMedID 32161776

    View details for PubMedCentralID PMC7062553

  • Femtosecond Compression Dynamics and Timing Jitter Suppression in a THz-driven Electron Bunch Compressor PHYSICAL REVIEW LETTERS Snively, E. C., Othman, M. K., Kozina, M., Ofori-Okai, B. K., Weathersby, S. P., Park, S., Shen, X., Wang, X. J., Hoffmann, M. C., Li, R. K., Nanni, E. A. 2020; 124 (5)
  • Light-induced charge density wave in LaTe3 NATURE PHYSICS Kogar, A., Zong, A., Dolgirev, P. E., Shen, X., Straquadine, J., Bie, Y., Wang, X., Rohwer, T., Tung, I., Yang, Y., Li, R., Yang, J., Weathersby, S., Park, S., Kozina, M. E., Sie, E. J., Wen, H., Jarillo-Herrero, P., Fisher, I. R., Wang, X., Gedik, N. 2020; 16 (2): 159-+
  • Nonequilibrium Thermodynamics of Colloidal Gold Nanocrystals Monitored by Ultrafast Electron Diffraction and Optical Scattering Microscopy. ACS nano Guzelturk, B. n., Utterback, J. K., Coropceanu, I. n., Kamysbayev, V. n., Janke, E. M., Zajac, M. n., Yazdani, N. n., Cotts, B. L., Park, S. n., Sood, A. n., Lin, M. F., Reid, A. H., Kozina, M. E., Shen, X. n., Weathersby, S. P., Wood, V. n., Salleo, A. n., Wang, X. n., Talapin, D. V., Ginsberg, N. S., Lindenberg, A. M. 2020


    Metal nanocrystals exhibit important optoelectronic and photocatalytic functionalities in response to light. These dynamic energy conversion processes have been commonly studied by transient optical probes to date, but an understanding of the atomistic response following photoexcitation has remained elusive. Here, we use femtosecond resolution electron diffraction to investigate transient lattice responses in optically excited colloidal gold nanocrystals, revealing the effects of nanocrystal size and surface ligands on the electron-phonon coupling and thermal relaxation dynamics. First, we uncover a strong size effect on the electron-phonon coupling, which arises from reduced dielectric screening at the nanocrystal surfaces and prevails independent of the optical excitation mechanism (i.e., inter- and intraband). Second, we find that surface ligands act as a tuning parameter for hot carrier cooling. Particularly, gold nanocrystals with thiol-based ligands show significantly slower carrier cooling as compared to amine-based ligands under intraband optical excitation due to electronic coupling at the nanocrystal/ligand interfaces. Finally, we spatiotemporally resolve thermal transport and heat dissipation in photoexcited nanocrystal films by combining electron diffraction with stroboscopic elastic scattering microscopy. Taken together, we resolve the distinct thermal relaxation time scales ranging from 1 ps to 100 ns associated with the multiple interfaces through which heat flows at the nanoscale. Our findings provide insights into optimization of gold nanocrystals and their thin films for photocatalysis and thermoelectric applications.

    View details for DOI 10.1021/acsnano.0c00673

    View details for PubMedID 32208676

  • Simultaneous observation of nuclear and electronic dynamics by ultrafast electron diffraction. Science (New York, N.Y.) Yang, J. n., Zhu, X. n., F Nunes, J. P., Yu, J. K., Parrish, R. M., Wolf, T. J., Centurion, M. n., Gühr, M. n., Li, R. n., Liu, Y. n., Moore, B. n., Niebuhr, M. n., Park, S. n., Shen, X. n., Weathersby, S. n., Weinacht, T. n., Martinez, T. J., Wang, X. n. 2020; 368 (6493): 885–89


    Simultaneous observation of nuclear and electronic motion is crucial for a complete understanding of molecular dynamics in excited electronic states. It is challenging for a single experiment to independently follow both electronic and nuclear dynamics at the same time. Here we show that ultrafast electron diffraction can be used to simultaneously record both electronic and nuclear dynamics in isolated pyridine molecules, naturally disentangling the two components. Electronic state changes (S1→S0 internal conversion) were reflected by a strong transient signal in small-angle inelastic scattering, and nuclear structural changes (ring puckering) were monitored by large-angle elastic diffraction. Supported by ab initio nonadiabatic molecular dynamics and diffraction simulations, our experiment provides a clear view of the interplay between electronic and nuclear dynamics of the photoexcited pyridine molecule.

    View details for DOI 10.1126/science.abb2235

    View details for PubMedID 32439793

  • Microscopic nonequilibrium energy transfer dynamics in a photoexcited metal/insulator heterostructure PHYSICAL REVIEW B Rothenbach, N., Gruner, M. E., Ollefs, K., Schmitz-Antoniak, C., Salamon, S., Zhou, P., Li, R., Mo, M., Park, S., Shen, X., Weathersby, S., Yang, J., Wang, X. J., Pentcheva, R., Wende, H., Bovensiepen, U., Sokolowski-Tinten, K., Eschenlohr, A. 2019; 100 (17)
  • Femtosecond gas-phase mega-electron-volt ultrafast electron diffraction. Structural dynamics (Melville, N.Y.) Shen, X., Nunes, J. P., Yang, J., Jobe, R. K., Li, R. K., Lin, M., Moore, B., Niebuhr, M., Weathersby, S. P., Wolf, T. J., Yoneda, C., Guehr, M., Centurion, M., Wang, X. J. 2019; 6 (5): 054305


    The development of ultrafast gas electron diffraction with nonrelativistic electrons has enabled the determination of molecular structures with atomic spatial resolution. It has, however, been challenging to break the picosecond temporal resolution barrier and achieve the goal that has long been envisioned-making space- and-time resolved molecular movies of chemical reaction in the gas-phase. Recently, an ultrafast electron diffraction (UED) apparatus using mega-electron-volt (MeV) electrons was developed at the SLAC National Accelerator Laboratory for imaging ultrafast structural dynamics of molecules in the gas phase. The SLAC gas-phase MeV UED has achieved 65 fs root mean square temporal resolution, 0.63A spatial resolution, and 0.22A-1 reciprocal-space resolution. Such high spatial-temporal resolution has enabled the capturing of real-time molecular movies of fundamental photochemical mechanisms, such as chemical bond breaking, ring opening, and a nuclear wave packet crossing a conical intersection. In this paper, the design that enables the high spatial-temporal resolution of the SLAC gas phase MeV UED is presented. The compact design of the differential pump section of the SLAC gas phase MeV UED realized five orders-of-magnitude vacuum isolation between the electron source and gas sample chamber. The spatial resolution, temporal resolution, and long-term stability of the apparatus are systematically characterized.

    View details for DOI 10.1063/1.5120864

    View details for PubMedID 31649964

  • Dynamical Slowing-Down in an Ultrafast Photoinduced Phase Transition. Physical review letters Zong, A., Dolgirev, P. E., Kogar, A., Ergeçen, E., Yilmaz, M. B., Bie, Y. Q., Rohwer, T., Tung, I. C., Straquadine, J., Wang, X., Yang, Y., Shen, X., Li, R., Yang, J., Park, S., Hoffmann, M. C., Ofori-Okai, B. K., Kozina, M. E., Wen, H., Wang, X., Fisher, I. R., Jarillo-Herrero, P., Gedik, N. 2019; 123 (9): 097601


    Complex systems, which consist of a large number of interacting constituents, often exhibit universal behavior near a phase transition. A slowdown of certain dynamical observables is one such recurring feature found in a vast array of contexts. This phenomenon, known as critical slowing-down, is well studied mostly in thermodynamic phase transitions. However, it is less understood in highly nonequilibrium settings, where the time it takes to traverse the phase boundary becomes comparable to the timescale of dynamical fluctuations. Using transient optical spectroscopy and femtosecond electron diffraction, we studied a photoinduced transition of a model charge-density-wave (CDW) compound LaTe_{3}. We observed that it takes the longest time to suppress the order parameter at the threshold photoexcitation density, where the CDW transiently vanishes. This finding can be captured by generalizing the time-dependent Landau theory to a system far from equilibrium. The experimental observation and theoretical understanding of dynamical slowing-down may offer insight into other general principles behind nonequilibrium phase transitions in many-body systems.

    View details for DOI 10.1103/PhysRevLett.123.097601

    View details for PubMedID 31524450

  • Parallel-plate waveguides for terahertz-driven MeV electron bunch compression OPTICS EXPRESS Othman, M. K., Hoffmann, M. C., Kozina, M. E., Wang, X. J., Li, R. K., Nanni, E. A. 2019; 27 (17): 23791–800
  • Diffractive imaging of dissociation and ground-state dynamics in a complex molecule PHYSICAL REVIEW A Wilkin, K. J., Parrish, R. M., Yang, J., Wolf, T. A., Nunes, J. F., Guehr, M., Li, R., Shen, X., Zheng, Q., Wang, X., Martinez, T. J., Centurion, M. 2019; 100 (2)
  • Optical Control of Non-Equilibrium Phonon Dynamics. Nano letters Krishnamoorthy, A., Lin, M., Zhang, X., Weninger, C., Ma, R., Britz, A., Tiwary, C. S., Kochat, V., Apte, A., Yang, J., Park, S., Li, R., Shen, X., Wang, X., Kalia, R., Nakano, A., Shimojo, F., Fritz, D., Bergmann, U., Ajayan, P., Vashishta, P. 2019


    The light-induced selective population of short-lived far-from-equilibrium vibration modes is a promising approach for controlling ultrafast and irreversible structural changes in functional nanomaterials. However, this requires a detailed understanding of the dynamics and evolution of these phonon modes and their coupling to the excited-state electronic structure. Here, we combine femtosecond mega-electronvolt electron diffraction experiments on a prototypical layered material, MoTe2, with non-adiabatic quantum molecular dynamics simulations and ab initio electronic structure calculations to show how non-radiative energy relaxation pathways for excited electrons can be tuned by controlling the optical excitation energy. We show how the dominant intravalley and intervalley scattering mechanisms for hot and band-edge electrons leads to markedly different transient phonon populations evident in electron diffraction patterns. This understanding of how tuning optical excitations affect phonon populations and atomic motion is critical for efficiently controlling light-induced structural transitions of optoelectronic devices.

    View details for DOI 10.1021/acs.nanolett.9b01179

    View details for PubMedID 31260315

  • The photochemical ring-opening of 1,3-cyclohexadiene imaged by ultrafast electron diffraction NATURE CHEMISTRY Wolf, T. A., Sanchez, D. M., Yang, J., Parrish, R. M., Nunes, J. F., Centurion, M., Coffee, R., Cryan, J. P., Guehr, M., Hegazy, K., Kirrander, A., Li, R. K., Ruddock, J., Shen, X., Vecchione, T., Weathersby, S. P., Weber, P. M., Wilkin, K., Yong, H., Zheng, Q., Wang, X. J., Minitti, M. P., Martinez, T. J. 2019; 11 (6): 504–9
  • Precision Plasmonics with Monomers and Dimers of Spherical Gold Nanoparticles: Nonequilibrium Dynamics at the Time and Space Limits JOURNAL OF PHYSICAL CHEMISTRY C Schumacher, L., Jose, J., Janoschka, D., Dreher, P., Davis, T. J., Ligges, M., Li, R., Mo, M., Park, S., Shen, X., Weathersby, S., Yang, J., Wang, X., Heringdorf, F., Sokolowski-Tinten, K., Schluecker, S. 2019; 123 (21): 13181-13191
  • Photoinduced dynamics of nematic order parameter in FeSe PHYSICAL REVIEW B Konstantinova, T., Wu, L., Abeykoon, M., Koch, R. J., Wang, A. F., Li, R. K., Shen, X., Li, J., Tao, J., Zaliznyak, I. A., Petrovic, C., Billinge, S. L., Wang, X. J., Bozin, E. S., Zhu, Y. 2019; 99 (18)
  • Visualization of ultrafast melting initiated from radiation-driven defects in solids SCIENCE ADVANCES Mo, M., Murphy, S., Chen, Z., Fossati, P., Li, R., Wang, Y., Wang, X., Glenzer, S. 2019; 5 (5): eaaw0392


    Materials exposed to extreme radiation environments such as fusion reactors or deep spaces accumulate substantial defect populations that alter their properties and subsequently the melting behavior. The quantitative characterization requires visualization with femtosecond temporal resolution on the atomic-scale length through measurements of the pair correlation function. Here, we demonstrate experimentally that electron diffraction at relativistic energies opens a new approach for studies of melting kinetics. Our measurements in radiation-damaged tungsten show that the tungsten target subjected to 10 displacements per atom of damage undergoes a melting transition below the melting temperature. Two-temperature molecular dynamics simulations reveal the crucial role of defect clusters, particularly nanovoids, in driving the ultrafast melting process observed on the time scale of less than 10 ps. These results provide new atomic-level insights into the ultrafast melting processes of materials in extreme environments.

    View details for DOI 10.1126/sciadv.aaw0392

    View details for Web of Science ID 000470125000088

    View details for PubMedID 31139748

    View details for PubMedCentralID PMC6534394

  • Terahertz-based subfemtosecond metrology of relativistic electron beams PHYSICAL REVIEW ACCELERATORS AND BEAMS Li, R. K., Hoffmann, M. C., Nanni, E. A., Glenzer, S. H., Kozina, M. E., Lindenberg, A. M., Ofori-Okai, B. K., Reid, A. H., Shen, X., Weathersby, S. P., Yang, J., Zajac, M., Wang, X. J. 2019; 22 (1)
  • An ultrafast symmetry switch in a Weyl semimetal. Nature Sie, E. J., Nyby, C. M., Pemmaraju, C. D., Park, S. J., Shen, X. n., Yang, J. n., Hoffmann, M. C., Ofori-Okai, B. K., Li, R. n., Reid, A. H., Weathersby, S. n., Mannebach, E. n., Finney, N. n., Rhodes, D. n., Chenet, D. n., Antony, A. n., Balicas, L. n., Hone, J. n., Devereaux, T. P., Heinz, T. F., Wang, X. n., Lindenberg, A. M. 2019; 565 (7737): 61–66


    Topological quantum materials exhibit fascinating properties1-3, with important applications for dissipationless electronics and fault-tolerant quantum computers4,5. Manipulating the topological invariants in these materials would allow the development of topological switching applications analogous to switching of transistors6. Lattice strain provides the most natural means of tuning these topological invariants because it directly modifies the electron-ion interactions and potentially alters the underlying crystalline symmetry on which the topological properties depend7-9. However, conventional means of applying strain through heteroepitaxial lattice mismatch10 and dislocations11 are not extendable to controllable time-varying protocols, which are required in transistors. Integration into a functional device requires the ability to go beyond the robust, topologically protected properties of materials and to manipulate the topology at high speeds. Here we use crystallographic measurements by relativistic electron diffraction to demonstrate that terahertz light pulses can be used to induce terahertz-frequency interlayer shear strain with large strain amplitude in the Weyl semimetal WTe2, leading to a topologically distinct metastable phase. Separate nonlinear optical measurements indicate that this transition is associated with a symmetry change to a centrosymmetric, topologically trivial phase. We further show that such shear strain provides an ultrafast, energy-efficient way of inducing robust, well separated Weyl points or of annihilating all Weyl points of opposite chirality. This work demonstrates possibilities for ultrafast manipulation of the topological properties of solids and for the development of a topological switch operating at terahertz frequencies.

    View details for PubMedID 30602749

  • THz-Pump UED-Probe on a Topological Weyl Semimetal Sie, E. J., Nyby, C. M., Pemmaraju, C. D., Park, S., Shen, X., Yang, J., Hoffmann, M. C., Ofori-Okai, B. K., Li, R., Reid, A. H., Weathersby, S., Mannebach, E., Finney, N., Rhodes, D., Chenet, D., Antony, A., Balicas, L., Hone, J., Devereaux, T. P., Heinz, T. F., Wang, X., Lindenberg, A. M., IEEE IEEE. 2019
  • Ultrafast manipulation of mirror domain walls in a charge density wave SCIENCE ADVANCES Zong, A., Shen, X., Kogar, A., Ye, L., Marks, C., Chowdhury, D., Rohwer, T., Freelon, B., Weathersby, S., Li, R., Yang, J., Checkelsky, J., Wang, X., Gedik, N. 2018; 4 (10): eaau5501


    Domain walls (DWs) are singularities in an ordered medium that often host exotic phenomena such as charge ordering, insulator-metal transition, or superconductivity. The ability to locally write and erase DWs is highly desirable, as it allows one to design material functionality by patterning DWs in specific configurations. We demonstrate such capability at room temperature in a charge density wave (CDW), a macroscopic condensate of electrons and phonons, in ultrathin 1T-TaS2. A single femtosecond light pulse is shown to locally inject or remove mirror DWs in the CDW condensate, with probabilities tunable by pulse energy and temperature. Using time-resolved electron diffraction, we are able to simultaneously track anti-synchronized CDW amplitude oscillations from both the lattice and the condensate, where photoinjected DWs lead to a red-shifted frequency. Our demonstration of reversible DW manipulation may pave new ways for engineering correlated material systems with light.

    View details for DOI 10.1126/sciadv.aau5501

    View details for Web of Science ID 000449221200072

    View details for PubMedID 30345365

    View details for PubMedCentralID PMC6195337

  • Determination of the electron-lattice coupling strength of copper with ultrafast MeV electron diffraction Mo, M. Z., Becker, V., Ofori-Okai, B. K., Shen, X., Chen, Z., Witte, B., Redmer, R., Li, R. K., Dunning, M., Weathersby, S. P., Wang, X. J., Glenzer, S. H. AMER INST PHYSICS. 2018: 10C108


    Electron-lattice coupling strength governs the energy transfer between electrons and the lattice and is important for understanding the material behavior under highly non-equilibrium conditions. Here we report the results of employing time-resolved electron diffraction at MeV energies to directly study the electron-lattice coupling strength in 40-nm-thick polycrystalline copper excited by femtosecond optical lasers. The temporal evolution of lattice temperature at various pump fluence conditions were obtained from the measurements of the Debye-Waller decay of multiple diffraction peaks. We observed the temperature dependence of the electron-lattice relaxation time which is a result of the temperature dependence of electron heat capacity. Comparison with two-temperature model simulations reveals an electron-lattice coupling strength of (0.9 ± 0.1) × 1017 W/m3/K for copper.

    View details for DOI 10.1063/1.5035368

    View details for Web of Science ID 000449144500023

    View details for PubMedID 30399817

  • Dynamics of Electron-Phonon Coupling in Bicontinuous Nanoporous Gold JOURNAL OF PHYSICAL CHEMISTRY C Zheng, Q., Shen, X., Sokolowski-Tinten, K., Li, R. K., Chen, Z., Mo, M. Z., Wang, Z. L., Weathersby, S. P., Yang, J., Chen, M. W., Wang, X. J. 2018; 122 (28): 16368–73
  • Imaging CF3I conical intersection and photodissociation dynamics with ultrafast electron diffraction. Science (New York, N.Y.) Yang, J., Zhu, X., Wolf, T. J., Li, Z., Nunes, J. P., Coffee, R., Cryan, J. P., Gühr, M., Hegazy, K., Heinz, T. F., Jobe, K., Li, R., Shen, X., Veccione, T., Weathersby, S., Wilkin, K. J., Yoneda, C., Zheng, Q., Martinez, T. J., Centurion, M., Wang, X. 2018; 361 (6397): 64-67


    Conical intersections play a critical role in excited-state dynamics of polyatomic molecules because they govern the reaction pathways of many nonadiabatic processes. However, ultrafast probes have lacked sufficient spatial resolution to image wave-packet trajectories through these intersections directly. Here, we present the simultaneous experimental characterization of one-photon and two-photon excitation channels in isolated CF3I molecules using ultrafast gas-phase electron diffraction. In the two-photon channel, we have mapped out the real-space trajectories of a coherent nuclear wave packet, which bifurcates onto two potential energy surfaces when passing through a conical intersection. In the one-photon channel, we have resolved excitation of both the umbrella and the breathing vibrational modes in the CF3 fragment in multiple nuclear dimensions. These findings benchmark and validate ab initio nonadiabatic dynamics calculations.

    View details for DOI 10.1126/science.aat0049

    View details for PubMedID 29976821

  • Heterogeneous to homogeneous melting transition visualized with ultrafast electron diffraction. Science (New York, N.Y.) Mo, M. Z., Chen, Z., Li, R. K., Dunning, M., Witte, B. B., Baldwin, J. K., Fletcher, L. B., Kim, J. B., Ng, A., Redmer, R., Reid, A. H., Shekhar, P., Shen, X. Z., Shen, M., Sokolowski-Tinten, K., Tsui, Y. Y., Wang, Y. Q., Zheng, Q., Wang, X. J., Glenzer, S. H. 2018; 360 (6396): 1451–55


    The ultrafast laser excitation of matters leads to nonequilibrium states with complex solid-liquid phase-transition dynamics. We used electron diffraction at mega-electron volt energies to visualize the ultrafast melting of gold on the atomic scale length. For energy densities approaching the irreversible melting regime, we first observed heterogeneous melting on time scales of 100 to 1000 picoseconds, transitioning to homogeneous melting that occurs catastrophically within 10 to 20 picoseconds at higher energy densities. We showed evidence for the heterogeneous coexistence of solid and liquid. We determined the ion and electron temperature evolution and found superheated conditions. Our results constrain the electron-ion coupling rate, determine the Debye temperature, and reveal the melting sensitivity to nucleation seeds.

    View details for DOI 10.1126/science.aar2058

    View details for PubMedID 29954977

  • A terahertz pump mega-electron-volt ultrafast electron diffraction probe apparatus at the SLAC Accelerator Structure Test Area facility JOURNAL OF INSTRUMENTATION Ofori-Okai, B. K., Hoffmann, M. C., Reid, A. H., Edstrom, S., Jobe, R. K., Li, R. K., Mannebach, E. M., Park, S. J., Polzin, W., Shen, X., Weathersby, S. P., Yang, J., Zheng, Q., Zajac, M., Lindenberg, A. M., Glenzer, S. H., Wang, X. J. 2018; 13
  • Nonequilibrium electron and lattice dynamics of strongly correlated Bi2Sr2CaCu2O8+delta single crystals SCIENCE ADVANCES Konstantinova, T., Rameau, J. D., Reid, A. H., Abdurazakov, O., Wu, L., Li, R., Shen, X., Gu, G., Huang, Y., Rettig, L., Avigo, I., Ligges, M., Freericks, J. K., Kemper, A. F., Duerr, H. A., Bovensiepen, U., Johnson, P. D., Wang, X., Zhu, Y. 2018; 4 (4): eaap7427


    The interplay between the electronic and lattice degrees of freedom in nonequilibrium states of strongly correlated systems has been debated for decades. Although progress has been made in establishing a hierarchy of electronic interactions with the use of time-resolved techniques, the role of the phonons often remains in dispute, a situation highlighting the need for tools that directly probe the lattice. We present the first combined megaelectron volt ultrafast electron diffraction and time- and angle-resolved photoemission spectroscopy study of optimally doped Bi2Sr2CaCu2O8+δ. Quantitative analysis of the lattice and electron subsystems' dynamics provides a unified picture of nonequilibrium electron-phonon interactions in the cuprates beyond the N-temperature model. The work provides new insights on the specific phonon branches involved in the nonequilibrium heat dissipation from the high-energy Cu-O bond stretching "hot" phonons to the lowest-energy acoustic phonons with correlated atomic motion along the <110> crystal directions and their characteristic time scales. It reveals a highly nonthermal phonon population during the first several picoseconds after the photoexcitation. The approach, taking advantage of the distinct nature of electrons and photons as probes, is applicable for studying energy relaxation in other strongly correlated electron systems.

    View details for DOI 10.1126/sciadv.aap7427

    View details for Web of Science ID 000431374900021

    View details for PubMedID 29719862

    View details for PubMedCentralID PMC5922801

  • Beyond a phenomenological description of magnetostriction NATURE COMMUNICATIONS Reid, A. H., Shen, X., Maldonado, P., Chase, T., Jal, E., Granitzka, P. W., Carva, K., Li, R. K., Li, J., Wu, L., Vecchione, T., Liu, T., Chen, Z., Higley, D. J., Hartmann, N., Coffee, R., Wu, J., Dakovski, G. L., Schlotter, W. F., Ohldag, H., Takahashi, Y. K., Mehta, V., Hellwig, O., Fry, A., Zhu, Y., Cao, J., Fullerton, E. E., Stohr, J., Oppeneer, P. M., Wang, X. J., Durr, H. A. 2018; 9: 388


    Magnetostriction, the strain induced by a change in magnetization, is a universal effect in magnetic materials. Owing to the difficulty in unraveling its microscopic origin, it has been largely treated phenomenologically. Here, we show how the source of magnetostriction-the underlying magnetoelastic stress-can be separated in the time domain, opening the door for an atomistic understanding. X-ray and electron diffraction are used to separate the sub-picosecond spin and lattice responses of FePt nanoparticles. Following excitation with a 50-fs laser pulse, time-resolved X-ray diffraction demonstrates that magnetic order is lost within the nanoparticles with a time constant of 146 fs. Ultrafast electron diffraction reveals that this demagnetization is followed by an anisotropic, three-dimensional lattice motion. Analysis of the size, speed, and symmetry of the lattice motion, together with ab initio calculations accounting for the stresses due to electrons and phonons, allow us to reveal the magnetoelastic stress generated by demagnetization.

    View details for PubMedID 29374151

  • Femtosecond mega-electron-volt electron microdiffraction ULTRAMICROSCOPY Shen, X., Li, R. K., Lundstrom, U., Lane, T. J., Reid, A. H., Weathersby, S. P., Wang, X. J. 2018; 184: 172–76


    To understand and control the basic functions of physical, chemical and biological processes from micron to nano-meter scale, an instrument capable of visualizing transient structural changes of inhomogeneous materials with atomic spatial and temporal resolutions, is required. One such technique is femtosecond electron microdiffraction, in which a short electron pulse with femtosecond-scale duration is focused into a micron-scale spot and used to obtain diffraction images to resolve ultrafast structural dynamics over a localized crystalline domain. In this letter, we report the experimental demonstration of time-resolved mega-electron-volt electron microdiffraction which achieves a 5 μm root-mean-square (rms) beam size on the sample and a 110 fs rms temporal resolution. Using pulses of 10k electrons at 4.2 MeV energy with a normalized emittance 3 nm-rad, we obtained high quality diffraction from a single 10 μm paraffin (C44H90) crystal. The phonon softening mode in optical-pumped polycrystalline Bi was also time-resolved, demonstrating the temporal resolution limits of the instrument. This new characterization capability will open many research opportunities in material and biological sciences.

    View details for DOI 10.1016/j.ultramic.2017.08.019

    View details for Web of Science ID 000415650200020

    View details for PubMedID 28915441

  • Carrier-Specific Femtosecond XUV Transient Absorption of PbI2 Reveals Ultrafast Nonradiative Recombination JOURNAL OF PHYSICAL CHEMISTRY C Lin, M., Verkamp, M. A., Leveillee, J., Ryland, E. S., Benke, K., Zhang, K., Weninger, C., Shen, X., Li, R., Fritz, D., Bergmann, U., Wang, X., Schleife, A., Vura-Weis, J. 2017; 121 (50): 27886–93
  • Ultrafast non-radiative dynamics of atomically thin MoSe2 NATURE COMMUNICATIONS Lin, M., Kochat, V., Krishnamoorthy, A., Bassman, L., Weninger, C., Zheng, Q., Zhang, X., Apte, A., Tiwary, C., Shen, X., Li, R., Kalia, R., Ajayan, P., Nakano, A., Vashishta, P., Shimojo, F., Wang, X., Fritz, D. M., Bergmann, U. 2017; 8: 1745


    Photo-induced non-radiative energy dissipation is a potential pathway to induce structural-phase transitions in two-dimensional materials. For advancing this field, a quantitative understanding of real-time atomic motion and lattice temperature is required. However, this understanding has been incomplete due to a lack of suitable experimental techniques. Here, we use ultrafast electron diffraction to directly probe the subpicosecond conversion of photoenergy to lattice vibrations in a model bilayered semiconductor, molybdenum diselenide. We find that when creating a high charge carrier density, the energy is efficiently transferred to the lattice within one picosecond. First-principles nonadiabatic quantum molecular dynamics simulations reproduce the observed ultrafast increase in lattice temperature and the corresponding conversion of photoenergy to lattice vibrations. Nonadiabatic quantum simulations further suggest that a softening of vibrational modes in the excited state is involved in efficient and rapid energy transfer between the electronic system and the lattice.

    View details for DOI 10.1038/s41467-017-01844-2

    View details for Web of Science ID 000416229300031

    View details for PubMedID 29170416

    View details for PubMedCentralID PMC5701075

  • Femtosecond MeV Electron Energy-Loss Spectroscopy PHYSICAL REVIEW APPLIED Li, R. K., Wang, X. J. 2017; 8 (5)
  • Electron-lattice energy relaxation in laser-excited thin-film Au-insulator heterostructures studied by ultrafast MeV electron diffraction STRUCTURAL DYNAMICS-US Sokolowski-Tinten, K., Shen, X., Zheng, Q., Chase, T., Coffee, R., Jerman, M., Li, R. K., Ligges, M., Makasyuk, I., Mo, M., Reid, A. H., Rethfeld, B., Vecchione, T., Weathersby, S. P., Durr, H. A., Wang, X. J. 2017; 4 (5): 054501


    We apply time-resolved MeV electron diffraction to study the electron-lattice energy relaxation in thin film Au-insulator heterostructures. Through precise measurements of the transient Debye-Waller-factor, the mean-square atomic displacement is directly determined, which allows to quantitatively follow the temporal evolution of the lattice temperature after short pulse laser excitation. Data obtained over an extended range of laser fluences reveal an increased relaxation rate when the film thickness is reduced or the Au-film is capped with an additional insulator top-layer. This behavior is attributed to a cross-interfacial coupling of excited electrons in the Au film to phonons in the adjacent insulator layer(s). Analysis of the data using the two-temperature-model taking explicitly into account the additional energy loss at the interface(s) allows to deduce the relative strength of the two relaxation channels.

    View details for DOI 10.1063/1.4995258

    View details for Web of Science ID 000414175400013

    View details for PubMedID 28795080

    View details for PubMedCentralID PMC5522339

  • Stacking order dynamics in the quasi-two-dimensional dichalcogenide 1T-TaS2 probed with MeV ultrafast electron diffraction STRUCTURAL DYNAMICS-US Le Guyader, L., Chase, T., Reid, A. H., Li, R. K., Svetin, D., Shen, X., Vecchione, T., Wang, X. J., Mihailovic, D., Durr, H. A. 2017; 4 (4): 044020


    Transitions between different charge density wave (CDW) states in quasi-two-dimensional materials may be accompanied also by changes in the inter-layer stacking of the CDW. Using MeV ultrafast electron diffraction, the out-of-plane stacking order dynamics in the quasi-two-dimensional dichalcogenide 1T-TaS2 is investigated for the first time. From the intensity of the CDW satellites aligned around the commensurate l = 1/6 characteristic stacking order, it is found out that this phase disappears with a 0.3 ps time constant. Simultaneously, in the same experiment, the emergence of the incommensurate phase, with a slightly slower 2.0 ps time constant, is determined from the intensity of the CDW satellites aligned around the incommensurate l = 1/3 characteristic stacking order. These results might be of relevance in understanding the metallic character of the laser-induced metastable "hidden" state recently discovered in this compound.

    View details for DOI 10.1063/1.4982918

    View details for Web of Science ID 000402004800020

    View details for PubMedID 28503631

    View details for PubMedCentralID PMC5415401

  • A direct electron detector for time-resolved MeV electron microscopy REVIEW OF SCIENTIFIC INSTRUMENTS Vecchione, T., Denes, P., Jobe, R. K., Johnson, I. J., Joseph, J. M., Li, R. K., Perazzo, A., Shen, X., Wang, X. J., WEATHERSBY, S. P., Yang, J., Zhang, D. 2017; 88 (3)


    The introduction of direct electron detectors enabled the structural biology revolution of cryogenic electron microscopy. Direct electron detectors are now expected to have a similarly dramatic impact on time-resolved MeV electron microscopy, particularly by enabling both spatial and temporal jitter correction. Here we report on the commissioning of a direct electron detector for time-resolved MeV electron microscopy. The direct electron detector demonstrated MeV single electron sensitivity and is capable of recording megapixel images at 180 Hz. The detector has a 15-bit dynamic range, better than 30-μm spatial resolution and less than 20 analogue-to-digital converter count RMS pixel noise. The unique capabilities of the direct electron detector and the data analysis required to take advantage of these capabilities are presented. The technical challenges associated with generating and processing large amounts of data are also discussed.

    View details for DOI 10.1063/1.4977923

    View details for Web of Science ID 000397871400027

    View details for PubMedID 28372435

  • Light-induced picosecond rotational disordering of the inorganic sublattice in hybrid perovskites. Science advances Wu, X. n., Tan, L. Z., Shen, X. n., Hu, T. n., Miyata, K. n., Trinh, M. T., Li, R. n., Coffee, R. n., Liu, S. n., Egger, D. A., Makasyuk, I. n., Zheng, Q. n., Fry, A. n., Robinson, J. S., Smith, M. D., Guzelturk, B. n., Karunadasa, H. I., Wang, X. n., Zhu, X. n., Kronik, L. n., Rappe, A. M., Lindenberg, A. M. 2017; 3 (7): e1602388


    Femtosecond resolution electron scattering techniques are applied to resolve the first atomic-scale steps following absorption of a photon in the prototypical hybrid perovskite methylammonium lead iodide. Following above-gap photoexcitation, we directly resolve the transfer of energy from hot carriers to the lattice by recording changes in the mean square atomic displacements on 10-ps time scales. Measurements of the time-dependent pair distribution function show an unexpected broadening of the iodine-iodine correlation function while preserving the Pb-I distance. This indicates the formation of a rotationally disordered halide octahedral structure developing on picosecond time scales. This work shows the important role of light-induced structural deformations within the inorganic sublattice in elucidating the unique optoelectronic functionality exhibited by hybrid perovskites and provides new understanding of hot carrier-lattice interactions, which fundamentally determine solar cell efficiencies.

    View details for PubMedID 28782016

  • Single-shot mega-electronvolt ultrafast electron diffraction for structure dynamic studies of warm dense matter REVIEW OF SCIENTIFIC INSTRUMENTS Mo, M. Z., Shen, X., Chen, Z., Li, R. K., Dunning, M., Sokolowski-Tinten, K., Zheng, Q., WEATHERSBY, S. P., Reid, A. H., Coffee, R., Makasyuk, I., Edstrom, S., McCormick, D., Jobe, K., Hast, C., Glenzer, S. H., Wang, X. 2016; 87 (11)


    We have developed a single-shot mega-electronvolt ultrafast-electron-diffraction system to measure the structural dynamics of warm dense matter. The electron probe in this system is featured by a kinetic energy of 3.2 MeV and a total charge of 20 fC, with the FWHM pulse duration and spot size at sample of 350 fs and 120 μm respectively. We demonstrate its unique capability by visualizing the atomic structural changes of warm dense gold formed from a laser-excited 35-nm freestanding single-crystal gold foil. The temporal evolution of the Bragg peak intensity and of the liquid signal during solid-liquid phase transition are quantitatively determined. This experimental capability opens up an exciting opportunity to unravel the atomic dynamics of structural phase transitions in warm dense matter regime.

    View details for DOI 10.1063/1.4960070

    View details for Web of Science ID 000390242300094

    View details for PubMedID 27910490

  • Diffractive Imaging of Coherent Nuclear Motion in Isolated Molecules PHYSICAL REVIEW LETTERS Yang, J., Guehr, M., Shen, X., Li, R., Vecchione, T., Coffee, R., Corbett, J., Fry, A., Hartmann, N., Hast, C., Hegazy, K., Jobe, K., Makasyuk, I., Robinson, J., Robinson, M. S., Vetter, S., Weathersby, S., Yoneda, C., Wang, X., Centurion, M. 2016; 117 (15)


    Observing the motion of the nuclear wave packets during a molecular reaction, in both space and time, is crucial for understanding and controlling the outcome of photoinduced chemical reactions. We have imaged the motion of a vibrational wave packet in isolated iodine molecules using ultrafast electron diffraction with relativistic electrons. The time-varying interatomic distance was measured with a precision 0.07 Å and temporal resolution of 230 fs full width at half maximum. The method is not only sensitive to the position but also the shape of the nuclear wave packet.

    View details for DOI 10.1103/PhysRevLett.117.153002

    View details for Web of Science ID 000384479300004

    View details for PubMedID 27768362

  • Diffractive imaging of a rotational wavepacket in nitrogen molecules with femtosecond megaelectronvolt electron pulses NATURE COMMUNICATIONS Yang, J., Guehr, M., Vecchione, T., Robinson, M. S., Li, R., Hartmann, N., Shen, X., Coffee, R., Corbett, J., Fry, A., Gaffney, K., Gorkhover, T., Hast, C., Jobe, K., Makasyuk, I., Reid, A., Robinson, J., Vetter, S., Wang, F., Weathersby, S., Yoneda, C., Centurion, M., Wang, X. 2016; 7


    Imaging changes in molecular geometries on their natural femtosecond timescale with sub-Angström spatial precision is one of the critical challenges in the chemical sciences, as the nuclear geometry changes determine the molecular reactivity. For photoexcited molecules, the nuclear dynamics determine the photoenergy conversion path and efficiency. Here we report a gas-phase electron diffraction experiment using megaelectronvolt (MeV) electrons, where we captured the rotational wavepacket dynamics of nonadiabatically laser-aligned nitrogen molecules. We achieved a combination of 100 fs root-mean-squared temporal resolution and sub-Angstrom (0.76 Å) spatial resolution that makes it possible to resolve the position of the nuclei within the molecule. In addition, the diffraction patterns reveal the angular distribution of the molecules, which changes from prolate (aligned) to oblate (anti-aligned) in 300 fs. Our results demonstrate a significant and promising step towards making atomically resolved movies of molecular reactions.

    View details for DOI 10.1038/ncomms11232

    View details for Web of Science ID 000373622400001

    View details for PubMedID 27046298

    View details for PubMedCentralID PMC4822053

  • Ultrafast electron diffraction from non-equilibrium phonons in femtosecond laser heated Au films APPLIED PHYSICS LETTERS Chase, T., Trigo, M., Reid, A. H., Li, R., Vecchione, T., Shen, X., Weathersby, S., Coffee, R., Hartmann, N., Reis, D. A., Wang, X. J., Duerr, H. A. 2016; 108 (4)

    View details for DOI 10.1063/1.4940981

    View details for Web of Science ID 000375217200022

  • Thickness-dependent electron-lattice equilibration in laser-excited thin bismuth films NEW JOURNAL OF PHYSICS Sokolowski-Tinten, K., Li, R. K., Reid, A. H., WEATHERSBY, S. P., QUIRIN, F., Chase, T., Coffee, R., Corbett, J., FRY, A., Hartmann, N., Hast, C., HETTEL, R., von Hoegen, M. H., Janoschka, D., LEWANDOWSKI, J. R., Ligges, M., Heringdorf, F. M., Shen, X., Vecchione, T., Witt, C., Wu, J., Duerr, H. A., Wang, X. J. 2015; 17
  • Dynamic Structural Response and Deformations of Monolayer MoS2 Visualized by Femtosecond Electron Diffraction NANO LETTERS Mannebach, E. M., Li, R., Duerloo, K., Nyby, C., Zalden, P., Vecchione, T., Ernst, F., Reid, A. H., Chase, T., Shen, X., Weathersby, S., Hast, C., Hettel, R., Coffee, R., Hartmann, N., Fry, A. R., Yu, Y., Cao, L., Heinz, T. F., Reed, E. J., Duerr, H. A., Wang, X., Lindenberg, A. M. 2015; 15 (10): 6889-6895


    Two-dimensional materials are subject to intrinsic and dynamic rippling that modulates their optoelectronic and electromechanical properties. Here, we directly visualize the dynamics of these processes within monolayer transition metal dichalcogenide MoS2 using femtosecond electron scattering techniques as a real-time probe with atomic-scale resolution. We show that optical excitation induces large-amplitude in-plane displacements and ultrafast wrinkling of the monolayer on nanometer length-scales, developing on picosecond time-scales. These deformations are associated with several percent peak strains that are fully reversible over tens of millions of cycles. Direct measurements of electron-phonon coupling times and the subsequent interfacial thermal heat flow between the monolayer and substrate are also obtained. These measurements, coupled with first-principles modeling, provide a new understanding of the dynamic structural processes that underlie the functionality of two-dimensional materials and open up new opportunities for ultrafast strain engineering using all-optical methods.

    View details for DOI 10.1021/acs.nanolett.5b02805

    View details for PubMedID 26322659

  • Mega-electron-volt ultrafast electron diffraction at SLAC National Accelerator Laboratory REVIEW OF SCIENTIFIC INSTRUMENTS WEATHERSBY, S. P., Brown, G., Centurion, M., CHASE, T. F., Coffee, R., Corbett, J., Eichner, J. P., Frisch, J. C., Fry, A. R., Guehr, M., Hartmann, N., Hast, C., HETTEL, R., Jobe, R. K., Jongewaard, E. N., LEWANDOWSKI, J. R., Li, R. K., Lindenberg, A. M., Makasyuk, I., May, J. E., McCormick, D., Nguyen, M. N., Reid, A. H., Shen, X., Sokolowski-Tinten, K., Vecchione, T., Vetter, S. L., Wu, J., Yang, J., Duerr, H. A., Wang, X. J. 2015; 86 (7)


    Ultrafast electron probes are powerful tools, complementary to x-ray free-electron lasers, used to study structural dynamics in material, chemical, and biological sciences. High brightness, relativistic electron beams with femtosecond pulse duration can resolve details of the dynamic processes on atomic time and length scales. SLAC National Accelerator Laboratory recently launched the Ultrafast Electron Diffraction (UED) and microscopy Initiative aiming at developing the next generation ultrafast electron scattering instruments. As the first stage of the Initiative, a mega-electron-volt (MeV) UED system has been constructed and commissioned to serve ultrafast science experiments and instrumentation development. The system operates at 120-Hz repetition rate with outstanding performance. In this paper, we report on the SLAC MeV UED system and its performance, including the reciprocal space resolution, temporal resolution, and machine stability.

    View details for DOI 10.1063/1.4926994

    View details for Web of Science ID 000358934400053

    View details for PubMedID 26233391

  • Femtosecond time-resolved MeV electron diffraction NEW JOURNAL OF PHYSICS Zhu, P., Zhu, Y., Hidaka, Y., Wu, L., Cao, J., Berger, H., Geck, J., Kraus, R., Pjerov, S., Shen, Y., Tobey, R. I., Hill, J. P., Wang, X. J. 2015; 17
  • Dynamic separation of electron excitation and lattice heating during the photoinduced melting of the periodic lattice distortion in 2H-TaSe2 APPLIED PHYSICS LETTERS Zhu, P., Cao, J., Zhu, Y., Geck, J., Hidaka, Y., Pjerov, S., Ritschel, T., Berger, H., Shen, Y., Tobey, R., Hill, J. P., Wang, X. J. 2013; 103 (7)

    View details for DOI 10.1063/1.4818460

    View details for Web of Science ID 000323769000029

  • Experimental demonstration of a slippage-dominant free-electron laser amplifier PHYSICAL REVIEW E Yang, X., Shen, Y., Podobedov, B., Hidaka, Y., Seletskiy, S., Wang, X. J. 2012; 85 (2): 026404


    We report the first experimental demonstration of a slippage-dominant free-electron laser (FEL) amplifier using a 140-fs full width at half maximum broadband seed laser pulse. The evolution of the longitudinal phase space of a laser seeded FEL amplifier in the slippage-dominant regime was experimentally characterized. We observed, for the first time, that the pulse duration of the FEL is primarily determined by the slippage between the seed laser and the electron beam. With a ± 1% variation in the electron-beam energy, we demonstrated reasonably good longitudinal coherence and a ± 2% spectral tuning range. The experimentally observed temporal and spectral evolution of the slippage-dominant FEL was verified by the numerical simulations.

    View details for DOI 10.1103/PhysRevE.85.026404

    View details for Web of Science ID 000300422900004

    View details for PubMedID 22463334

  • Initial source of microbunching instability studies in a free electron laser injector PHYSICAL REVIEW SPECIAL TOPICS-ACCELERATORS AND BEAMS Seletskiy, S., Hidaka, Y., Murphy, J. B., Podobedov, B., Qian, H., Shen, Y., Wang, X. J., Yang, X. 2011; 14 (11)
  • Tunable Few-Cycle and Multicycle Coherent Terahertz Radiation from Relativistic Electrons PHYSICAL REVIEW LETTERS Shen, Y., Yang, X., Carr, G. L., Hidaka, Y., Murphy, J. B., Wang, X. 2011; 107 (20): 204801


    We report the generation of tunable, narrow-band, few-cycle and multicycle coherent terahertz (THz) pulses from a temporally modulated relativistic electron beam. We demonstrate that the frequency of the THz radiation and the number of the oscillation cycles of the THz electric field can be tuned by changing the modulation period of the electron beam through a temporally shaped photocathode drive laser. The central frequency of the THz spectrum is tunable from ∼0.26 to 2.6 THz with a bandwidth of ∼0.16  THz.

    View details for DOI 10.1103/PhysRevLett.107.204801

    View details for Web of Science ID 000297133700006

    View details for PubMedID 22181737

  • Surface photoemission in a high-brightness electron beam radio frequency gun APPLIED PHYSICS LETTERS Qian, H. J., Murphy, J. B., Shen, Y., Tang, C. X., Wang, X. J. 2010; 97 (25)

    View details for DOI 10.1063/1.3531561

    View details for Web of Science ID 000285764300090

  • Electro-optic time lensing with an intense single-cycle terahertz pulse PHYSICAL REVIEW A Shen, Y., Carr, G. L., Murphy, J. B., Tsang, T. Y., Wang, X., Yang, X. 2010; 81 (5)
  • Electron bunch length monitors using spatially encoded electro-optical technique in an orthogonal configuration APPLIED PHYSICS LETTERS Yang, X., Tsang, T., Rao, T., Murphy, J. B., Shen, Y., Wang, X. J. 2009; 95 (23)

    View details for DOI 10.1063/1.3266919

    View details for Web of Science ID 000272627700006

  • Efficiency and Spectrum Enhancement in a Tapered Free-Electron Laser Amplifier PHYSICAL REVIEW LETTERS Wang, X. J., Freund, H. P., Harder, D., Miner, W. H., Murphy, J. B., Qian, H., Shen, Y., Yang, X. 2009; 103 (15): 154801


    We report the first experimental characterization of efficiency and spectrum enhancement in a laser-seeded free-electron laser using a tapered undulator. Output and spectra in the fundamental and third harmonic were measured versus distance for uniform and tapered undulators. With a 4% field taper over 3 m, a 300% (50%) increase in the fundamental (third harmonic) output was observed. A significant improvement in the spectra with the elimination of sidebands was observed using a tapered undulator. The experiment is in good agreement with predictions using the MEDUSA simulation code.

    View details for DOI 10.1103/PhysRevLett.103.154801

    View details for Web of Science ID 000270672100033

    View details for PubMedID 19905644

  • Experimental demonstration of high quality MeV ultrafast electron diffraction REVIEW OF SCIENTIFIC INSTRUMENTS Li, R., Tang, C., Du, Y., Huang, W., Du, Q., Shi, J., Yan, L., Wang, X. 2009; 80 (8): 083303


    The simulation optimization and an experimental demonstration of improved performances of mega-electron-volt ultrafast electron diffraction (MeV UED) are reported in this paper. Using ultrashort high quality electron pulses from an S-band photocathode rf gun and a polycrystalline aluminum foil as the sample, we experimentally demonstrated an improved spatial resolution of MeV UED, in which the Debye-Scherrer rings of the (111) and (200) planes were clearly resolved. This result showed that MeV UED is capable to achieve an atomic level spatial resolution and a approximately 100 fs temporal resolution simultaneously, and will be a unique tool for ultrafast structural dynamics studies.

    View details for DOI 10.1063/1.3194047

    View details for Web of Science ID 000270084000009

    View details for PubMedID 19725647

  • Measurement of femtosecond electron pulse length and the temporal broadening due to space charge REVIEW OF SCIENTIFIC INSTRUMENTS Wang, X., Nie, S., Park, H., Li, J., Clinite, R., Li, R., Wang, X., Cao, J. 2009; 80 (1): 013902


    The temporal width of ultrashort electron pulses as a function of beam intensity was measured on the femtosecond time scale with a customized streak camera. The results show that the temporal profile of an electron pulse is Gaussian at low beam intensity and progressively evolves to a top-hat shape due to space charge broadening as the beam intensity increases. The strong correlation between the pulse width and beam intensity observed in our streaking measurements agrees very well with the mean-field calculation and supports the main conclusion of previous theoretical studies that the space charge broadening plays a determinant role.

    View details for DOI 10.1063/1.3062863

    View details for Web of Science ID 000262966000020

    View details for PubMedID 19191442

  • Recent progress of a soft X-ray generation system based on inverse Compton scattering at Waseda University Sakaue, K., Gowa, T., Hayano, H., Kamiya, Y., Kashiwagi, S., Kuroda, R., Masuda, A., Moriyama, R., Urakawa, J., Ushida, K., Wang, X., Washio, M. PERGAMON-ELSEVIER SCIENCE LTD. 2008: 1136-1141
  • Spatiotemporal control of ultrashort laser pulses using intense single-cycle terahertz pulses PHYSICAL REVIEW A Shen, Y., Carr, G. L., Murphy, J. B., Tsang, T. Y., Wang, X., Yang, X. 2008; 78 (4)
  • Exponential growth, superradiance, and tunability of a seeded free electron laser OPTICS EXPRESS Wu, J., Murphy, J. B., Wang, X., Wang, K. 2008; 16 (5): 3255-3260


    Exponential growth and superradiance regimes in a high-gain free electron laser (FEL) are studied in this paper for both a seeded FEL and a Self-Amplified Spontaneous Emission (SASE) FEL. The results are compared to the earlier superrdaince theory and the recent experimental observation. The influence of an initial energy chirp along the electron bunch on the superradiance mode is explored for the first time. With a short seed to increase the initial seed bandwidth, a tunable seeded FEL is possible.

    View details for PubMedID 18542413

  • Laser-seeded free-electron lasers at the NSLS Synchrotron Radiat.News Murphy, J. B., Wang, X. 2008: 41-44
  • Efficiency enhancement using electron energy detuning in a laser seeded free electron laser amplifier APPLIED PHYSICS LETTERS Wang, X. J., Watanabe, T., Shen, Y., Li, R. K., Murphy, J. B., Tsang, T. 2007; 91 (18)

    View details for DOI 10.1063/1.2803772

    View details for Web of Science ID 000250643600015

  • Nonlinear cross-phase modulation with intense single-cycle terahertz pulses PHYSICAL REVIEW LETTERS Shen, Y., Watanabe, T., Arena, D. A., Kao, C., Murphy, J. B., Tsang, T. Y., Wang, X. J., Carr, G. L. 2007; 99 (4): 043901


    We have demonstrated nonlinear cross-phase modulation in electro-optic crystals using intense, single-cycle terahertz (THz) radiation. Individual THz pulses, generated by coherent transition radiation emitted by subpicosecond electron bunches, have peak energies of up to 100 microJ per pulse. The time-dependent electric field of the intense THz pulses induces cross-phase modulation in electro-optic crystals through the Pockels effect, leading to spectral shifting, broadening, and modulation of copropagating laser pulses. The observed THz-induced cross-phase modulation agrees well with a time-dependent phase-shift model.

    View details for DOI 10.1103/PhysRevLett.99.043901

    View details for Web of Science ID 000248345800027

    View details for PubMedID 17678365

  • High power beam test and measurement of emittance evolution of a 1.6-cell photocathode RF gun at Pohang Accelerator Laboratory JAPANESE JOURNAL OF APPLIED PHYSICS PART 1-REGULAR PAPERS BRIEF COMMUNICATIONS & REVIEW PAPERS Park, J., Park, S., Kim, C., Parc, Y., Hong, J., Huang, J., Xiang, D., Wang, X., Ko, I. 2007; 46 (4A): 1751-1756
  • Interplay of the chirps and chirped pulse compression in a high-gain seeded free-electron laser JOURNAL OF THE OPTICAL SOCIETY OF AMERICA B-OPTICAL PHYSICS Wu, J., Murphy, J. B., Emma, P. J., Wang, X., Watanabe, T., Zhong, X. 2007; 24 (3): 484-495
  • Experimental characterization of superradiance in a single-pass high-gain laser-seeded free-electron laser amplifier PHYSICAL REVIEW LETTERS Watanabe, T., Wang, X. J., Murphy, J. B., Rose, J., Shen, Y., Tsang, T., Giannessi, L., Musumeci, P., Reiche, S. 2007; 98 (3): 034802


    In this Letter we report the first experimental characterization of superradiance in a single-pass high-gain free-electron laser (FEL) seeded by a 150 femtosecond (FWHM) Ti:sapphire laser. The nonlinear energy gain after an exponential gain regime was observed. We also measured the evolution of the longitudinal phase space in both the exponential and superradiant regimes. The output FEL pulse duration was measured to be as short as 81 fs, a roughly 50% reduction compared to the input seed laser. The temporal distribution of the FEL radiation as predicted by a numerical simulation was experimentally verified for the first time.

    View details for DOI 10.1103/PhysRevLett.98.034802

    View details for Web of Science ID 000243587200027

    View details for PubMedID 17358688

  • Potential of femtosecond electron diffraction using near-relativistic electrons from a photocathode RF electron gun JOURNAL OF THE KOREAN PHYSICAL SOCIETY Wang, X. J., Xiang, D., Kim, T. K., Ihee, H. 2006; 48 (3): 390-396
  • NSLS II: The future of the NSLS Murphy, J. B., Bengtsson, J., Biscardi, R., Blednykh, A., Carr, L., Casey, W., Chouhan, S., Dierker, S., Haas, E., Heese, R., Hulbert, S., Johnson, E., Kao, C. C., Kramer, S., Krinsky, S., Pinayev, Pjerov, S., Podobedov, B., Rakowsky, G., Rose, J., Shaftan, T., Sheehy, B., Skaritka, J., Towne, N., Wang, J. M., Wang, X. J., Yu, L. H., IEEE IEEE. 2005: 1584-1586
  • Electron beam phase-space measurement using a high-precision tomography technique PHYSICAL REVIEW SPECIAL TOPICS-ACCELERATORS AND BEAMS Yakimenko, Babzien, M., Ben-Zvi, Malone, R., Wang, X. J. 2003; 6 (12)
  • First ultraviolet high-gain harmonic-generation free-electron laser PHYSICAL REVIEW LETTERS Yu, L. H., DiMauro, L., Doyuran, A., Graves, W. S., Johnson, E. D., Heese, R., Krinsky, S., Loos, H., Murphy, J. B., Rakowsky, G., Rose, J., Shaftan, T., Sheehy, B., Skaritka, J., Wang, X. J., Wu, Z. 2003; 91 (7): 074801


    We report the first experimental results on a high-gain harmonic-generation (HGHG) free-electron laser (FEL) operating in the ultraviolet. An 800 nm seed from a Ti:sapphire laser has been used to produce saturated amplified radiation at the 266 nm third harmonic. The results confirm the predictions for HGHG FEL operation: stable central wavelength, narrow bandwidth, and small pulse-energy fluctuation.

    View details for DOI 10.1103/PhysRevLett.91.074801

    View details for Web of Science ID 000184815400026

    View details for PubMedID 12935021

  • First SASE and seeded FEL lasing of the NSLS DUV FEL at 266 and 400 nm DiMauro, L., Doyuran, A., Graves, W., Heese, R., Johnson, E. D., Krinsky, S., Loos, H., Murphy, J. B., Rakowsky, G., Rose, J., Shaftan, T., Sheehy, B., Skaritka, J., Wang, X. J., Yu, L. H. ELSEVIER SCIENCE BV. 2003: 15-18
  • Results of the VISA SASE FEL experiment at 840 nm NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH SECTION A-ACCELERATORS SPECTROMETERS DETECTORS AND ASSOCIATED EQUIPMENT Murokh, A., Agustsson, R., Babzien, M., Ben-Zvi, I., Bertolini, L., van Bibber, K., Carr, R., Cornacchia, M., Frigola, P., Hill, J., JOHNSON, E., Klaisner, L., Le Sage, G., Libkind, M., Malone, R., Nuhn, H. D., Pellegrini, C., Reiche, S., Rakowsky, G., Rosenzweig, J., Ruland, R., Skaritka, J., Toor, A., Tremaine, A., Wang, X., Yakimenko, V. 2003; 507 (1-2): 417-421
  • Design considerations for the LCLS Limborg, C. ELSEVIER SCIENCE BV. 2003: 378-381
  • Femto-seconds kilo-ampere electron beam generation Wang, X. J., Chang, X. Y. ELSEVIER SCIENCE BV. 2003: 310-313
  • Properties of the ultrashort gain length, self-amplified spontaneous emission free-electron laser in the linear regime and saturation PHYSICAL REVIEW E Murokh, A., Agustsson, R., Babzien, M., Ben-Zvi, I., Bertolini, L., van Bibber, K., Carr, R., Cornacchia, M., Frigola, P., Hill, J., JOHNSON, E., Klaisner, L., Le Sage, G., Libkind, M., Malone, R., Nuhn, H. D., Pellegrini, C., Reiche, S., Rakowsky, G., Rosenzweig, J., Ruland, R., Skaritka, J., Toor, A., Tremaine, A., Wang, X., Yakimenko, V. 2003; 67 (6)


    VISA (Visible to Infrared SASE Amplifier) is a high-gain self-amplified spontaneous emission (SASE) free-electron laser (FEL), which achieved saturation at 840 nm within a single-pass 4-m undulator. The experiment was performed at the Accelerator Test Facility at BNL, using a high brightness 70-MeV electron beam. A gain length shorter than 18 cm has been obtained, yielding a total gain of 2 x 10(8) at saturation. The FEL performance, including the spectral, angular, and statistical properties of SASE radiation, has been characterized for different electron beam conditions. Results are compared to the three-dimensional SASE FEL theory and start-to-end numerical simulations of the entire injector, transport, and FEL systems. An agreement between simulations and experimental results has been obtained at an unprecedented level of detail.

    View details for DOI 10.1103/PhysRevE.67.066501

    View details for Web of Science ID 000184085000076

    View details for PubMedID 16241361

  • Surface-roughness wakefield measurements at Brookhaven Accelerator Test Facility PHYSICAL REVIEW LETTERS Zhou, F., Wu, J. H., Babzien, M., Ben-Zvi, Malone, R., Murphy, J. B., Wang, X. J., Woodle, M. H., Yakimenko 2002; 89 (17): 174801


    An experiment has been carried out at the Brookhaven Accelerator Test Facility to investigate the effect of a surface-roughness wakefield in narrow beam tubes with artificially created bumps. The measurements show that the synchronous modes decay significantly due to the randomization of the roughness pattern. It is pointed out that this decay mechanism has not been investigated in the previous experiment at DESY and the investigators' conclusion does not apply for surface-roughness wakefields in real surfaces.

    View details for DOI 10.1103/PhysRevLett.89.174801

    View details for Web of Science ID 000178483500026

    View details for PubMedID 12398674

  • Fundamental and harmonic microbunching in a high-gain self-amplified spontaneous-emission free-electron laser PHYSICAL REVIEW E Tremaine, A., Wang, X. J., Babzien, M., Ben-Zvi, Cornacchia, M., Murokh, A., Nuhn, H. D., Malone, R., Pellegrini, C., Reiche, S., Rosenzweig, J., Skaritka, J., Yakimenko 2002; 66 (3): 036503


    Electron beam microbunching in both the fundamental and second harmonic in a high-gain self-amplified spontaneous emission free-electron laser (SASE FEL) was experimentally characterized using coherent transition radiation. The microbunching factors for both modes (b(1) and b(2)) approach unity, an indication of FEL saturation. These measurements are compared to the predictions of FEL simulations. The simultaneous capture of the microbunching and SASE radiation for individual micropulses correlate the longitudinal electron beam structure with the FEL gain.

    View details for DOI 10.1103/PhysRevE.66.036503

    View details for Web of Science ID 000178624400027

    View details for PubMedID 12366273

  • Experimental characterization of emittance growth induced by the nonuniform transverse laser distribution in a photoinjector PHYSICAL REVIEW SPECIAL TOPICS-ACCELERATORS AND BEAMS Zhou, F., Ben-Zvi, Babzien, M., Chang, X. Y., Doyuran, A., Malone, R., Wang, X. J., Yakimenko 2002; 5 (9)
  • Experimental characterization of nonlinear harmonic radiation from a visible self-amplified spontaneous emission free-electron laser at saturation PHYSICAL REVIEW LETTERS Tremaine, A., Wang, X. J., Babzien, M., Ben-Zvi, Cornacchia, M., Nuhn, H. D., Malone, R., Murokh, A., Pellegrini, C., Reiche, S., Rosenzweig, J., Yakimenko 2002; 88 (20): 204801


    Nonlinear harmonic radiation was observed using the VISA self-amplified, spontaneous emission (SASE) free-electron laser (FEL) at saturation. The gain lengths, spectra, and energies of the three lowest SASE FEL modes were experimentally characterized. The measured nonlinear harmonic gain lengths and center spectral wavelengths decrease with harmonic number, n, which is consistent with nonlinear harmonic theory. Both the second and third nonlinear harmonics energies are about 1% of the fundamental energy. These experimental results demonstrate for the first time the feasibility of using nonlinear harmonic SASE FEL radiation to produce coherent, femtosecond x rays.

    View details for DOI 10.1103/PhysRevLett.88.204801

    View details for Web of Science ID 000175466200017

    View details for PubMedID 12005570

  • Photoinjector design for the LCLs Bolton, P. R., Clendenin, J. E., Dowell, D. H., Ferrario, M., Fisher, A. S., Gierman, S. M., Kirby, R. E., Krejcik, P., Limborg, C. G., Mulhollan, G. A., Nguyen, D., Palmer, D. T., Rosenzweig, J. B., Schmerge, J. F., Serafini, L., Wang, X. J. ELSEVIER SCIENCE BV. 2002: 296-300
  • Characterization of an 800 nm SASE FEL at saturation Tremaine, A., Frigola, P., Murokh, A., Pellegrini, C., Reiche, S., Rosenzweig, J., Babzien, M., Ben-Zvi, Johnson, E., Malone, R., Rakowsky, G., Skaritka, J., Wang, X. J., Van Bibber, K. A., Bertolini, L., Hill, J. M., Le Sage, G. P., Libkind, M., Toor, A., Carr, R., Cornacchia, M., Klaisner, L., Nuhn, H. D., Ruland, R. ELSEVIER. 2002: 24-28
  • Submicron emittance and ultra small beam size measurements at ATF Yakimenko, Babzien, M., Ben-Zvi, Malone, R., Wang, X. J. ELSEVIER SCIENCE BV. 2002: 277-281
  • Nonlinear harmonics in the high-gain harmonic generation (HGHG) experiment Biedron, S. G., Freund, H. P., Milton, S. V., Yu, L. H., Wang, X. J. ELSEVIER SCIENCE BV. 2001: 118-126
  • Characterization of a high-gain harmonic-generation free-electron laser at saturation PHYSICAL REVIEW LETTERS Doyuran, A., Babzien, M., Shaftan, T., Yu, L. H., DiMauro, L. F., Ben-Zvi, Biedron, S. G., Graves, W., Johnson, E., Krinsky, S., Malone, R., Pogorelsky, Skaritka, J., Rakowsky, G., Wang, X. J., Woodle, M., Yakimenko, Jagger, J., Sajaev, Vasserman 2001; 86 (26): 5902-5905


    We report on an experimental investigation characterizing the output of a high-gain harmonic-generation (HGHG) free-electron laser (FEL) at saturation. A seed CO2 laser at a wavelength of 10.6 microm was used to generate amplified FEL output at 5.3 microm. Measurement of the frequency spectrum, pulse duration, and correlation length of the 5.3 microm output verified that the light is longitudinally coherent. Investigation of the electron energy distribution and output harmonic energies provides evidence for saturated HGHG FEL operation.

    View details for DOI 10.1103/PhysRevLett.86.5902

    View details for Web of Science ID 000169484200015

    View details for PubMedID 11415390

  • Exponential gain and saturation of a self-amplified spontaneous emission free-electron laser SCIENCE Milton, S. V., Gluskin, E., Arnold, N. D., Benson, C., Berg, W., Biedron, S. G., Borland, M., Chae, Y. C., Dejus, R. J., Den Hartog, P. K., Deriy, B., Erdmann, M., Eidelmann, Y. I., Hahne, M. W., Huang, Z., Kim, K. J., Lewellen, J. W., Li, Y., Lumpkin, A. H., Makarov, O., Moog, E. R., Nassiri, A., Sajaev, Soliday, R., Tieman, B. J., Trakhtenberg, E. M., Travish, G., Vasserman, I. B., Vinokurov, N. A., Wang, X. J., Wiemerslage, G., Yang, B. X. 2001; 292 (5524): 2037-2041


    Self-amplified spontaneous emission in a free-electron laser has been proposed for the generation of very high brightness coherent x-rays. This process involves passing a high-energy, high-charge, short-pulse, low-energy-spread, and low-emittance electron beam through the periodic magnetic field of a long series of high-quality undulator magnets. The radiation produced grows exponentially in intensity until it reaches a saturation point. We report on the demonstration of self-amplified spontaneous emission gain, exponential growth, and saturation at visible (530 nanometers) and ultraviolet (385 nanometers) wavelengths. Good agreement between theory and simulation indicates that scaling to much shorter wavelengths may be possible. These results confirm the physics behind the self-amplified spontaneous emission process and forward the development of an operational x-ray free-electron laser.

    View details for DOI 10.1126/science.1059955

    View details for Web of Science ID 000169284700037

    View details for PubMedID 11358995

  • Observation of high-intensity X-rays in inverse Compton scattering experiment Kashiwagi, S., Washio, M., Kobuki, T., Kuroda, R., Ben-Zvi, Pogorelsky, Kusche, K., Skaritka, J., Yakimenko, Wang, X. J., Hirose, T., Dobashi, K., Muto, T., Urakawa, J., Omori, T., Okugi, T., Tsunemi, A., Liu, Y., He, P., Cline, D., Segalov, Z. ELSEVIER SCIENCE BV. 2000: 36-40
  • A new chemical analysis system using a photocathode RF gun Aoki, Y., Yang, J. F., Hirose, M., Sakai, F., Tsunemi, A., Yorozu, M., Okada, Y., Endo, A., Wang, X. J., Ben-Zvi ELSEVIER SCIENCE BV. 2000: 99-103
  • High-gain harmonic-generation free-electron laser SCIENCE Yu, L. H., Babzien, M., Ben-Zvi, DiMauro, L. F., Doyuran, A., Graves, W., Johnson, E., Krinsky, S., Malone, R., Pogorelsky, Skaritka, J., Rakowsky, G., Solomon, L., Wang, X. J., Woodle, M., Yakimenko, Biedron, S. G., Galayda, J. N., Gluskin, E., Jagger, J., Sajaev, Vasserman 2000; 289 (5481): 932-934


    A high-gain harmonic-generation free-electron laser is demonstrated. Our approach uses a laser-seeded free-electron laser to produce amplified, longitudinally coherent, Fourier transform-limited output at a harmonic of the seed laser. A seed carbon dioxide laser at a wavelength of 10.6 micrometers produced saturated, amplified free-electron laser output at the second-harmonic wavelength, 5.3 micrometers. The experiment verifies the theoretical foundation for the technique and prepares the way for the application of this technique in the vacuum ultraviolet region of the spectrum, with the ultimate goal of extending the approach to provide an intense, highly coherent source of hard x-rays.

    View details for DOI 10.1126/science.289.5481.932

    View details for Web of Science ID 000088701200026

    View details for PubMedID 10937992

  • Observation of self-amplified spontaneous emission and exponential growth at 530 nm PHYSICAL REVIEW LETTERS Milton, S. V., Gluskin, E., Biedron, S. G., Dejus, R. J., Den Hartog, P. K., Galayda, J. N., Kim, K. J., Lewellen, J. W., Moog, E. R., Sajaev, Sereno, N. S., Travish, G., Vinokurov, N. A., Arnold, N. D., Benson, C., Berg, W., Biggs, J. A., Borland, M., Carwardine, J. A., Chae, Y. C., Decker, G., Deriy, B. N., Erdmann, M. J., Friedman, H., Gold, C., Grelick, A. E., Hahne, M. W., Harkay, K. C., Huang, Z., Lessner, E. S., Lill, R. M., Lumpkin, A. H., Makarov, O. A., Markovich, G. M., Meyer, D., Nassiri, A., Noonan, Pasky, S. J., Pile, G., Smith, T. L., Soliday, R., Tieman, B. J., Trakhtenberg, E. M., Trento, G. F., Vasserman, I. B., Walters, D. R., Wang, X. J., Wiemerslage, G., Xu, S., Yang, B. X. 2000; 85 (5): 988-991


    Experimental evidence for self-amplified spontaneous emission (SASE) at 530 nm is reported. The measurements were made at the low-energy undulator test line facility at the Advanced Photon Source, Argonne National Laboratory. The experimental setup and details of the experimental results are presented, as well as preliminary analysis. This experiment extends to shorter wavelengths the operational knowledge of a linac-based SASE free-electron laser and explicitly shows the predicted exponential growth in intensity of the optical pulse as a function of length along the undulator.

    View details for DOI 10.1103/PhysRevLett.85.988

    View details for Web of Science ID 000088457000022

    View details for PubMedID 10991456

  • First lasing of a high-gain harmonic generation free- electron laser experiment Yu, L. H., Babzien, M., Ben-Zvi, DiMauro, L. F., Doyuran, A., Graves, W., Johnson, E., Krinsky, S., Malone, R., Pogorelsky, Skaritka, J., Rakowsky, G., Solomon, L., Wang, X. J., Woodle, M., Yakimenko, Biedron, S. G., Galayda, J. N., Gluskin, E., Jagger, J., Sajaev, Vassserman ELSEVIER SCIENCE BV. 2000: 301-306
  • Using a commercial mathematics software package for on-line analysis at the BNL Accelerator Test Facility Malone, R., Wang, X. J. IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC. 2000: 288-292

    View details for DOI 10.1109/23.846166

    View details for Web of Science ID 000087474200054

  • Measurement of electron-beam bunch length and emittance using shot-noise-driven fluctuations in incoherent radiation PHYSICAL REVIEW LETTERS Catravas, P., Leemans, W. P., Wurtele, J. S., Zolotorev, M. S., Babzien, M., Ben-Zvi, Segalov, Z., Wang, X. J., Yakimenko 1999; 82 (26): 5261-5264
  • Producing and measuring small electron bunches 1999 Particle Accelerator Conference Wang, X. IEEE. 1999: 229-233

    View details for DOI 10.1109/PAC.1999.795671

  • Experimental observation of femtosecond electron beam microbunching by inverse free-electron-laser acceleration PHYSICAL REVIEW LETTERS Liu, Y., Wang, X. J., Cline, D. B., Babzien, M., Fang, J. M., Gallardo, J., Kusche, K., Pogorelsky, Skaritka, J., van Steenbergen, A. 1998; 80 (20): 4418-4421
  • Observation of self-amplified spontaneous emission in the near-infrared and visible wavelengths PHYSICAL REVIEW E Babzien, M., Ben-Zvi, Catravas, P., Fang, J. M., Marshall, T. C., Wang, X. J., Wurtele, J. S., Yakimenko, Yu, L. H. 1998; 57 (5): 6093-6100
  • Observation of energy gain at the BNL inverse free-electron-laser accelerator (vol 77, pg 2690, 1996) PHYSICAL REVIEW LETTERS vanSteenbergen, A., Gallardo, J., Sandweiss, J., Fang, J. M., Babzien, M., Qiu, Skaritka, J., Wang, X. J. 1996; 77 (20): 4280
  • Experimental observation of high-brightness microbunching in a photocathode rf electron gun PHYSICAL REVIEW E Wang, X. J., Qiu, BenZvi 1996; 54 (4): R3121-R3124
  • Experimental characterization of the high-brightness electron photoinjector Wang, X. J., Babzien, M., Batchelor, K., BenZvi, Malone, R., Pogorelsky, Qui, Sheehan, J., Sharitka, J., SrinivasanRao, T. ELSEVIER SCIENCE BV. 1996: 82-86
  • Demonstration of emittance compensation through the measurement of the slice emittance of a 10-ps electron bunch PHYSICAL REVIEW LETTERS Qiu, Batchelor, K., BenZvi, Wang, X. J. 1996; 76 (20): 3723-3726

    View details for DOI 10.1103/PhysRevLett.76.3723

    View details for Web of Science ID A1996UK56000016

    View details for PubMedID 10061093


    View details for DOI 10.1103/PhysRevLett.74.546

    View details for Web of Science ID A1995QC05600016

    View details for PubMedID 10058785


    View details for DOI 10.1063/1.351763

    View details for Web of Science ID A1992JF86800010