Dynamics of valence-shell electrons and nuclei probed by strong-field holography and rescattering

June 15, 2017

Imaging ultrafast dynamics of molecules on femtosecond to attosecond timescales

Time-resolved measurements of molecular dynamics have made substantial progress over the past years. In particular, electronic dynamics in atoms and molecules have become accessible through recent developments in attosecond and strong-field science. In this study, the authors transposed photoelectron holography and LIED from static systems to probing coupled electronic and nuclear dynamics in molecules. They first concentrated on purely electronic dynamics and show that a valence-shell electron wave packet leads to a very strong contrast modulation of the holographic fringes. Their calculations traced the origin of this effect to the time dependence of the momentum-space electron wavefunction, which modulates the amplitude ratio and the relative phases of scattering and non-scattering trajectories. They then investigated the manifestation of coupled electronic and nuclear dynamics taking place on similar time scales. They found signatures of both types of dynamics in photoelectron holography, but LIED is found to be almost exclusively sensitive to the nuclear dynamics. These results suggest avenues for disentangling electronic and nuclear dynamics in molecules, which is particularly interesting in the case of non-adiabatic dynamics, such as those occurring at conical intersections.

Figure 1: Discerning electronic and nuclear dynamics. (a) The top panel illustrates the prepared electronic and rotational dynamics with the left part showing the time-evolution of the one-electron wave function in NO and the right part illustrating the molecular-axis distribution. The wave function can be chosen real-valued with opposite signs (red and blue) by multiplication with a global phase factor that corresponds to a physically irrelevant shift of the absolute energy scale. The middle panel shows the time-dependent normalized NO⁺ yield (blue line) and a sine function with a period of 277 fs (red line). The lowest panel shows the calculated alignment dynamics expressed by 〈cos²θ〉 (including volume averaging). (b) Photoelectron momentum distribution of excited NO molecules recorded at a delay of 1.56 ps. Normalized difference S(t₁, t₂) (defined in the text) of momentum distributions measured at the minimum and maximum of the NO⁺ signal dominated by electronic dynamics (c, t₁=1.56 ps and t₂=1.72 ps, respectively) or around the rotational revival (d, at t₁=4.91 ps and t₂=5.10 ps, respectively). a.u., atomic units.

Reference:  Walt, S. G., N. Bhargava Ram, M. Atala, N. I. Shvetsov-Shilovski, A. von Conta, D. Baykusheva, M. Lein and H. J. Wörner (2017). Dynamics of valence-shell electrons and nuclei probed by strong-field holography and rescattering.  8: 15651. (10.1038/ncomms15651) Walt-2017 (2.65 MB)

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