From Event: SPIE Optical Engineering + Applications, 2017
Ultrafast electron diffraction (UED) has the potential to capture changes in the structure of isolated molecules on the natural spatial and temporal scale of chemical reactions, that is, sub-Angstrom changes in the atomic positions that happen on femtosecond time scales. UED has the advantage that electron sources can easily reach sub-Angstrom spatial resolution, but so far femtosecond resolution had not been available for gas phase experiments due to the challenges in delivering short enough electron pulses on a gas target and the velocity mismatch between laser and electron pulses. Recently, we have used relativistic electron pulses at MeV energy to solve these challenges and reach femtosecond resolution. We have, for the first time, imaged coherent nuclear motion in a molecule with UED. In a proof-of-principle experiment, we captured the motion of a laser-excited vibrational wavepacket in iodine molecules. We are currently performing experiments in more complex molecules to capture laser-induced dissociation and conformational changes. We have also developed a table top 100 keV source that relies on a pulse compressor to deliver femtosecond electron pulses on a target and uses a tilted laser pulse to compensate for the velocity mismatch between the laser and the electrons. This source has a high repetition rate that will complement the high temporal resolution of the relativistic source.
Martin Centurion, Jie Yang, Markus Guehr, Xiaozhe Shen, Renkai Li, Omid Zandi, Kyle J. Wilkin, Theodore Vecchione, Ryan N. Coffee, Jeff Corbett, Alan R. Fry, Nick Hartmann, Carsten Hast, Kareem Hegazy, Keith R. Jobe, Igor V. Makasyuk, Joseph S. Robinson, Matthew S. Robinson, Sharon Vetter, Stephen P. Weathersby, Chales Yoneda, and Xijie Wang, "Ultrafast imaging of molecular dynamics with electron diffraction (Conference Presentation)," Proc. SPIE 10380, Ultrafast Nonlinear Imaging and Spectroscopy V, 103800C (Presented at SPIE Optical Engineering + Applications: August 06, 2017; Published: 19 September 2017); https://doi.org/10.1117/12.2273479.5581151968001.
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