Abstract

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Ultrafast electron diffractive imaging with sub-Angstrom resolution

I-02

Ultrafast electron diffractive imaging with sub-Angstrom resolution


Martin Centurion1*

1University of Nebraska, Lincoln, USA

Ultrafast electron diffraction (UED) is a powerful tool to image structures with atomic resolution on femtosecond time scales. UED has been applied to investigate transient states in isolated molecules, but progress has been hampered by the limited temporal resolution and the random orientation of molecules in the gas phase. While gas UED experiments have reached picosecond resolution [1], diffraction from molecules in the gas phase presents unique challenges that have so far prevented the resolution from reaching the range of 100 fs that is needed to follow atomic motions. An additional challenge is the random orientation of the molecules, which greatly diminishes the information contained in the diffraction patterns and prevents the reconstruction of the structure directly from the data. We have recently shown sub-ps resolution and that by diffracting from impulsively aligned molecules it is possible to retrieve a molecular image directly from the data [2,3]. We have so far succeeded in recording static 3D molecular images and in recording the structure of a transient excited state [4]. We are currently pursuing two approaches to improve on the temporal resolution. The first is to use an RF cavity to compress sub-relativistic electron pulses, in combination with a tilted front pulse laser excitation to match the speed of electrons and laser through the sample. The second is the use femtosecond electron pulses with MeV energy where the velocity mismatch is not significant. We anticipate that these efforts will transition gas UED well into the femtosecond regime.

References:

[1] H. Ihee, V. A. Lobastov, U. M. Gomez, B. M. Goodson, R. Srinivasan, C. Y. Ruan, A. H. Zewail, Science 291, 458 (2001).

[2] C. J. Hensley, J. Yang, M. Centurion, Phys. Rev. Lett. 109, 133202 (2012).

[3] J. Yang, V. Makhija, V. Kumarappan, M. Centurion, Structural Dynamics 1, 044101 (2014).

[4] J. Yang, J. Beck, C. J. Uiterwaal, M. Centurion (manuscript under review).