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Full-Text Articles in Physics

Imaging Electronic Motions By Ultrafast Electron Diffraction, Hua-Chieh Shao, Anthony F. Starace Oct 2017

Imaging Electronic Motions By Ultrafast Electron Diffraction, Hua-Chieh Shao, Anthony F. Starace

Anthony F. Starace Publications

Recently ultrafast electron diffraction and microscopy have reached unprecedented temporal resolution, and transient structures with atomic precision have been observed in various reactions. It is anticipated that these extraordinary advances will soon allow direct observation of electronic motions during chemical reactions. We therefore performed a series of theoretical investigations and simulations to investigate the imaging of electronic motions in atoms and molecules by ultrafast electron diffraction. Three prototypical electronic motions were considered for hydrogen atoms. For the case of a breathing mode, the electron density expands and contracts periodically, and we show that the time-resolved scattering intensities reflect such changes ...


Ultrafast Imaging Of Isolated Molecules With Electron Diffraction, Martin Centurion Feb 2016

Ultrafast Imaging Of Isolated Molecules With Electron Diffraction, Martin Centurion

Martin Centurion Publications

Recent advances in ultrafast electron diffraction offer the possibility to image isolated molecules with sub-Angstrom spatial resolution in ultrafast time scales. In particular, diffraction from aligned molecules has opened the door to retrieving three-dimensional structures directly from experimental data. In this manuscript we review the progress in ultrafast gas electron diffraction and discuss remaining challenges to achieve a temporal resolution of sub-100 fs, which is needed to observe the nuclear motion in chemical reactions in the gas phase.


Gas-Phase Electron Diffraction From Laser-Aligned Molecules, Jie Yang, Martin Centurion Aug 2015

Gas-Phase Electron Diffraction From Laser-Aligned Molecules, Jie Yang, Martin Centurion

Martin Centurion Publications

Electron diffraction is a valuable tool to capture structural information from molecules in the gas phase. However, the information contained in the diffraction patterns is limited due to the random orientation of the molecules. Additional structural information can be retrieved if the molecules are aligned. Molecules can be impulsively aligned with femtosecond laser pulses, producing a transient alignment. The alignment persists only for a time on the order of a picosecond, so a pulsed electron gun is needed to record the diffraction patterns. In this manuscript, we describe the alignment process and show the changes in the diffraction pattern as ...


Tilted Femtosecond Pulses For Velocity Matching In Gas-Phase Ultrafast Electron Diffraction, Ping Zhang, Jie Yang, Martin Centurion Jan 2014

Tilted Femtosecond Pulses For Velocity Matching In Gas-Phase Ultrafast Electron Diffraction, Ping Zhang, Jie Yang, Martin Centurion

Martin Centurion Publications

Recent advances in pulsed electron gun technology have resulted in femtosecond electron pulses becoming available for ultrafast electron diffraction experiments. For experiments investigating chemical dynamics in the gas phase, the resolution is still limited to picosecond time scales due to the velocity mismatch between laser and electron pulses. Tilted laser pulses can be used for velocity matching, but thus far this has not been demonstrated over an extended target in a diffraction setting. We demonstrate an optical configuration to deliver high-intensity laser pulses with a tilted pulse front for velocity matching over the typical length of a gas jet. A ...


Tilted Femtosecond Pulses For Velocity Matching In Gas-Phase Ultrafast Electron Diffraction, Ping Zhang, Jie Yang, Martin Centurion Jan 2014

Tilted Femtosecond Pulses For Velocity Matching In Gas-Phase Ultrafast Electron Diffraction, Ping Zhang, Jie Yang, Martin Centurion

Martin Centurion Publications

Recent advances in pulsed electron gun technology have resulted in femtosecond electron pulses becoming available for ultrafast electron diffraction experiments. For experiments investigating chemical dynamics in the gas phase, the resolution is still limited to picosecond time scales due to the velocity mismatch between laser and electron pulses. Tilted laser pulses can be used for velocity matching, but thus far this has not been demonstrated over an extended target in a diffraction setting. We demonstrate an optical configuration to deliver high-intensity laser pulses with a tilted pulse front for velocity matching over the typical length of a gas jet. A ...