Who I am

I am the principal investigator of the Non-Periodic Imaging task at Stanford PULSE Institute, an independent laboratory of Stanford University and a staff scientist at SLAC National Accelerator Laboratory . We lead the effort on X-ray imaging of ultrafast atomic motion and transient structure in molecules, and study the nature of short wavelength strong field interaction with bound and free electrons. My goal is to develop and apply experimental and computational ultrafast scattering approaches to image quantum dynamics in real space to study and understand mechanisms that involve structural dynamics and electronic motion in photoexcited molecules of increased complexity and in complex environments. I received my PhD in Physics from the Weizmann Institute of Science, where I worked with Prof. Yaron Silberberg on coherent control, strong field interaction, nonlinear spectroscopy, and quantum optics.

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Stuff I do

• Research

• Publications

• Codes

• Misc

Ultrashort CV

Professional Experience:

SLAC National Accelerator Laboratory, Staff Scientist, 2022-today
SLAC National Accelerator Laboratory, Associate Staff Scientist, 2017-2022
SLAC National Accelerator Laboratory, Research Associate, 2014-2017
Stanford University, Applied Physics, Postdoctoral fellow, 2011-2014

Education:

Weizmann Institute of Science, PhD Physics, 2009
Weizmann Institute of Science, M.Sc Biological Physics, 2004
Hebrew University, Jerusalem, Israel, B.Sc Physics, 2001

Research

Studying matter and dynamics at the level of electrons and atoms requires imaging structures and motions in the sub-Ångstrom to nanometer and attosecond to picosecond scales, as in these ranges the fundamental properties of materials and physical mechanisms are established. State-of-the-art instruments such as X-ray free electron lasers, and ultrafast electrons are emerging tools that transform several fields of science because they access the atomic length and time scales without affecting the sample. Here we develop ultrafast scattering approaches to image quantum dynamics in real space to study and understand the interplay between photoabsorption, coherent electronic and nuclear motions, decoherence and energy redistribution.

Imaging coherent dynamics in complex environments

We led the first high-energy (18 keV) ultrafast X-ray scattering experiment in solution aiming to understand the role of coherent solute motions in complex environments on solvation and energy transfer dynamics. Applying advanced imaging methods, we decompose ultrafast solvation dynamics into specific changes in the solute and solute-solvent pair distribution function and directly trace the spatiotemporal shape of coherent vibrational wavepacket motions of different atom-pairs that take place simultaneously. Comparing to hybrid QM/MM trajectory simulations we retrieve the ground and excited state pair density distributions of the isotropic and anisotropic solute and solute-solvent terms in sub-Ångstrom resolutions. Combining high-energy X-rays with extreme brilliance and time resolution enables us to robustly characterize the non-equilibrium properties of molecules with atomic-scale resolution in time and space, presenting a significant opportunity to advance the discovery of design rules for controlling excited states.

Imaging Coherent to Thermal Photophysics of Transition Metal Complexes

We led an LCLS beam time to study the photo-physics of iron pentacarbonyl (Fe(CO)₅) and were able to resolve in space and time excited state dynamics that were not observed before. We have evidence that the metal-to-ligand charge-transfer (MLCT) transition creates a coherent vibration in the trigonal bipyramidal complex that in turn induce a synchronized sequential dissociation of the first CO ligand. We also observe a second thermal CO loss with a striking different rate where the ligand is restricted in real space near the parent molecule.

Super-resolution in Ultrafast Scattering

Direct real-space recovery of general and complex atomic motions is still mostly limited to signal interpretation in reciprocal space using system-dependent simulations, due to the insufficient scattering vector and photon energies available. We show how to extend super-resolution methods that transformed microscopy and bio-imaging, to the challenging case of ultrafast scattering, where traditional imaging optics, engineered single-emitters, or access to multiple scattering and high spatial frequencies are not available. We introduce theoretically and demonstrate experimentally an inversion and super-resolution method that allows the recovery of multiple sub-diffraction-limit spaced atomic distances from noisy signals. The approach directly brings real-space atomic resolutions to the ultrafast timescale, where often only spectroscopic information is recorded.

Imaging Strong-Field Induced Motion using High-Order Anisotropy X-ray Scattering

We have demonstrated the first ultrafast X-ray scattering of strongly driven molecular systems and analysis of high-order anisotropic components of the scattering signal, up to four-photon absorption. We outlined a method to analyze the scattering signal connecting the high-order anisotropy measured by the detector and the theoretical anisotropy scattering curves. We experimentally observed a multitude of dissociation and vibration motions simultaneously arising from various multiphoton transitions and used the anisotropy information of the scattering signal to disentangle the different processes and assign their dissociation velocities on the Ångström and femtosecond scales de-novo. The approach we demonstrated opens the way to image strong-field-induced motions directly.

Energy Resolved Scattering

We are developing methods to resolve and control the bandwidth of x-ray scattering signals, which will be a significant step forward in uncovering electronic motions in photo-excited systems. We have led beamtime in SSRL, collaborating with H. Yavas (LCLS), to characterize the energy resolution and fidelity trade-offs of a novel non-uniformly segmented spherical crystal analyzer that we have designed and fabricated, measuring the bandwidth response as a function of various properties of the analyzer segments, such as their area and aspect ratios.

Past Projects:

Singularities in strong-field dissociation

We study two types of singularities in strong field dissociation, the Light-induced conical intersection (LICI), and the cusp-type angular focusing. Conical intersections (CI) are natural degeneracies between Born-Oppenheimer surfaces that facilitate non-radiative energy transfer between electronic states, and play an important role in molecular dynamics. LICIs are degeneracies in the light-induced dressed state basis of the Born-Oppenheimer surfaces. Unlike ordinary CIs, the LICIs can be realized even in diatomic molecules, because the laser polarization adds an additional degree of freedom. We have demonstrated the effect LICI has on the driven diatomic system (H₂⁺), manifested in angular distribution modulations that result from the topological singularity induced by intense laser pulses. A different type of singularity that is under study is a cusp-type catastrophe that originates from angular focusing of nonresonant vibration states. When these states are coupled to strong fields, the cusp is observed in angle-resolved H₂⁺ photo-dissociation over a broad kinetic energy release range.

Attosecond dynamics in above-threshold ionization

We have measured the relative phase of different above-threshold ionization (ATI) peaks in a manner that is analogous to the XUV single photon phase measurements that employ RABBITT or the attosecond streak camera. This is multi-path interference of adjacent ATI peaks by a weak probe field at half the frequency. Sideband peaks appear due to absorption or emission of a single probe photon from adjacent ATI levels. We were able to resolve phase delays in ATI as function of the probe field delay to attosecond accuracy. We are expanding these observations to incorporate more detailed angular information, and also to study different regimes of strong-field ionization

Strong field atomic and molecular physics with velocity map imaging

We developed velocity map imaging modalities and analysis tools to study various aspects of strong field interaction. These methods were used to study attosecond time-resolved photoelectron holography and laser induced electron diffraction, to discover angle resolved phase-shifts in photoionization, uncover electron-molecular-frame dynamics in atomic and molecular systems, and for attosecond X-ray pulse characterization.

Publications

Google Scholar | Academia.edu

 

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Codes

"A man must have a code." (Bunk Moreland)

GitHub | Matlab File Exchange

Dark Mode Plot Transform your MATLAB plots to fit dark mode theme backgrounds! The function test which of the figure colors are not suitable to be used over a dark background (via color contrast), and adjust colors accordingly using a desaturation and brightness approach. download.

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Misc