X-Ray Sum Frequency Diffraction for Direct Imaging of Ultrafast Electron Dynamics

Journal Article · 11 June 2018 · Physical Review Letters

DOI: https://doi.org/10.1103/physrevlett.120.243902 · OSTI ID:1541326

Rouxel, Jérémy R. ^[1]; Kowalewski, Markus ^[2]; Bennett, Kochise ^[2]; Mukamel, Shaul ^[2]

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1. Univ. of California, Irvine, CA (United States). Dept. of Chemistry. Dept. of Physics and Astronomy; DOE/OSTI
2. Univ. of California, Irvine, CA (United States). Dept. of Chemistry. Dept. of Physics and Astronomy

X-ray diffraction from molecules in the ground state produces an image of their charge density, and time-resolved x-ray diffraction can thus monitor the motion of the nuclei. However, the density change of excited valence electrons upon optical excitation can barely be monitored with regular diffraction techniques due to the overwhelming background contribution of the core electrons. We present a nonlinear x-ray technique made possible by novel free electron laser sources, which provides a spatial electron density image of valence electron excitations. The technique, sum frequency generation carried out with a visible pump and a broadband x-ray diffraction pulse, yields snapshots of the transition charge densities, which represent the electron density variations upon optical excitation. The technique is illustrated by ab initio simulations of transition charge density imaging for the optically induced electronic dynamics in a donor or acceptor substituted stilbene.

• Research Organization: Univ. of California, Irvine, CA (United States)
• Sponsoring Organization: USDOE Office of Science (SC), Basic Energy Sciences (BES)
• Grant/Contract Number: FG02-04ER15571
• OSTI ID: 1541326
• Journal Information: Physical Review Letters, Journal Name: Physical Review Letters Journal Issue: 24 Vol. 120; ISSN 0031-9007
• Publisher: American Physical Society (APS)Copyright Statement
• Country of Publication: United States
• Language: English