Currently, our general approach to retrieving molecular structures from ultrafast gas-phase diffraction heavily relies on complex ab initio electronic or vibrational excited state simulations to make ...conclusive interpretations. Without such simulations, inverting this measurement for the structural probability distribution is typically intractable. This creates a so-called inverse problem. Here we address this inverse problem by developing a broadly applicable method that approximates the molecular frame structure |Ψ(R, t)|2 distribution independent of these complex simulations. We retrieve the vibronic ground state |Ψ(R)|2 for both simulated stretched NO2 and measured N2O. From measured N2O, we observe 40 mÅ coordinate-space resolution from 3.75 Å-1 reciprocal space range and poor signal-to-noise, a 50X improvement over traditional Fourier transform methods. In simulated NO2 diffraction experiments, typical to high signal-to-noise levels predict 100–1000X resolution improvements, down to 0.1 mÅ. By directly measuring the width of |Ψ(R)|2, we open ultrafast gas-phase diffraction capabilities to measurements beyond current analysis approaches. This method has the potential to effectively turn gas-phase ultrafast diffraction into a discovery-oriented technique to probe systems that are prohibitively difficult to simulate.
Dipole and quadrupole solitons in a two‐dimensional photorefractive optical lattice are investigated both theoretically and experimentally. It is shown theoretically that out‐of‐phase dipole solitons ...and quadrupole solitons exist and are linearly stable in the intermediate‐intensity regime. In‐phase dipole and quadrupole solitons, however, are always linearly unstable, but their instabilities are rather weak in the low‐intensity regime. Experimentally, both types of dipole solitons are observed, and the experimental results agree qualitatively with the theoretical predictions. In addition, we have observed the anisotropic effect of the photorefractive crystal in the dipole‐soliton formation.
We present results on ultrafast gas electron diffraction (UGED) experiments with femtosecond resolution using the MeV electron gun at SLAC National Accelerator Laboratory. UGED is a promising method ...to investigate molecular dynamics in the gas phase because electron pulses can probe the structure with a high spatial resolution. Until recently, however, it was not possible for UGED to reach the relevant timescale for the motion of the nuclei during a molecular reaction. Using MeV electron pulses has allowed us to overcome the main challenges in reaching femtosecond resolution, namely delivering short electron pulses on a gas target, overcoming the effect of velocity mismatch between pump laser pulses and the probe electron pulses, and maintaining a low timing jitter. At electron kinetic energies above 3 MeV, the velocity mismatch between laser and electron pulses becomes negligible. The relativistic electrons are also less susceptible to temporal broadening due to the Coulomb force. One of the challenges of diffraction with relativistic electrons is that the small de Broglie wavelength results in very small diffraction angles. In this paper we describe the new setup and its characterization, including capturing static diffraction patterns of molecules in the gas phase, finding time-zero with sub-picosecond accuracy and first time-resolved diffraction experiments. The new device can achieve a temporal resolution of 100 fs root-mean-square, and sub-angstrom spatial resolution. The collimation of the beam is sufficient to measure the diffraction pattern, and the transverse coherence is on the order of 2 nm. Currently, the temporal resolution is limited both by the pulse duration of the electron pulse on target and by the timing jitter, while the spatial resolution is limited by the average electron beam current and the signal-to-noise ratio of the detection system. We also discuss plans for improving both the temporal resolution and the spatial resolution.
Nature Commun Phys 6, 325 (2023) Currently, our general approach to retrieving molecular structures from
ultrafast gas-phase diffraction heavily relies on complex ab initio electronic
or vibrational ...excited state simulations to make conclusive interpretations.
Without such simulations, inverting this measurement for the structural
probability distribution is typically intractable. This creates a so-called
inverse problem. In this work, we develop a broadly applicable method that
addresses this inverse problem by approximating the molecular frame structure
$|\Psi(\boldsymbol{R}, t)|^2$ distribution independent of these complex
simulations. We retrieve the vibronic ground state $|\Psi(\boldsymbol{R})|^2$
for both simulated stretched NO$_2$ and measured N$_2$O. From measured N$_2$O,
we observe 40 mAngstroms coordinate-space resolution from 3.75 inverse
Angstroms reciprocal space range and poor signal-to-noise, a 50X improvement
over traditional Fourier transform methods. In simulated NO$_2$, typical to
high signal-to-noise levels predict 100--1000X resolution improvements, down to
0.1 mAngstroms. By directly measuring the width of $|\Psi(\boldsymbol{R})|^2$,
we open ultrafast gas-phase diffraction capabilities to measurements beyond
current analysis approaches. This method has the potential to effectively turn
gas-phase ultrafast diffraction into a discovery-oriented technique to probe
systems that are prohibitively difficult to simulate.
Currently, our general approach to retrieving molecular structures from ultrafast gas-phase diffraction heavily relies on complex ab initio electronic or vibrational excited state simulations to make ...conclusive interpretations. Without such simulations, inverting this measurement for the structural probability distribution is typically intractable. This creates a so-called inverse problem. In this work, we develop a broadly applicable method that addresses this inverse problem by approximating the molecular frame structure \(|\Psi(\boldsymbol{R}, t)|^2\) distribution independent of these complex simulations. We retrieve the vibronic ground state \(|\Psi(\boldsymbol{R})|^2\) for both simulated stretched NO\(_2\) and measured N\(_2\)O. From measured N\(_2\)O, we observe 40 mAngstroms coordinate-space resolution from 3.75 inverse Angstroms reciprocal space range and poor signal-to-noise, a 50X improvement over traditional Fourier transform methods. In simulated NO\(_2\), typical to high signal-to-noise levels predict 100--1000X resolution improvements, down to 0.1 mAngstroms. By directly measuring the width of \(|\Psi(\boldsymbol{R})|^2\), we open ultrafast gas-phase diffraction capabilities to measurements beyond current analysis approaches. This method has the potential to effectively turn gas-phase ultrafast diffraction into a discovery-oriented technique to probe systems that are prohibitively difficult to simulate.
Observing the motion of the nuclear wavepackets 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 wavepacket 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 (FWHM). The method is not only sensitive to the position but also the shape of the nuclear wavepacket.
Imaging changes in molecular geometries on their natural femtosecond timescale with sub-Angstrom spatial precision is one of the critical challenges in the chemical sciences, since the nuclear ...geometry changes determine the molecular reactivity. For photoexcited molecules, the nuclear dynamics determine the photoenergy conversion path and efficiency. We performed 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 an unprecedented combination of 100 fs root-mean-squared (RMS) 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.
We report on the frst experimental observation of discrete vortex solitons in
two-dimensional optically-induced photonic lattices. We demonstrate strong
stabilization of an optical vortex by the ...lattice in a self-focusing nonlinear
medium and study the generation of the discrete vortices from a broad class of
singular beams.
We report on the frst experimental observation of discrete vortex solitons in two-dimensional optically-induced photonic lattices. We demonstrate strong stabilization of an optical vortex by the ...lattice in a self-focusing nonlinear medium and study the generation of the discrete vortices from a broad class of singular beams.
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