Towards Imaging a Molecular Reaction

Observing in real time the dynamics of electrons in a chemical bond is one of the goals of ultrafast intense laser science. We have shown that electron rearrangement in the valence shell of the dissociating bromine molecule can be imaged by strong-field ionization during its transition from molecule to atoms. Theoretical results for the total ionization signals (see Figure) are in good agreement with experimental data, obtained in the Kapteyn-Murnane group. Characteristic changes in the signals can be attributed to dominant contributions from different orbitals during the dissociation. Our results show a molecular-like response for long times after the initiation of the dissociation and, hence, up to large internuclear distances.

Further, results of numerical simulations for the hydrogen molecular ion show how ultrashort laser pulse technology can be used to image a nuclear wave packet during the dissociation of a diatomic molecule. From the two-center interference patterns in the ionization yields dynamic information about the wavepacket, namely its velocity, mean internuclear distance and spreading, can be retrieved - in collaboration with M. Murnane and H. Kapteyn (JILA).

A. Jaron-Becker, IEEE Journ. Select. Topics Quant. Electron. 18, 105 (2012)
A. Picon et al., Phys. Rev. A 83, 013414 (2011)
W. Li et al., Proc. Nat. Acad. Sciences U.S.A. 107, 20219 (2010)

JILA research highlight (Br2): The Long Goodbye.

Imaging an Expanding Cluster

We showed that high harmonic generation cannot only be used to image microscopic distances, but it is also capable to retrieve time-resolved information about a complex system such as an expanding cluster. The proposed method is based on a pump-probe laser scheme in which the first pulse induces the cluster expansion and the time-delayed second pulse is used to generate higher-oder harmonics in the exploding cluster. The results of nur numerical simulations show that the dependence of the harmonic signal on the pump-probe delay provides information about the particle density and the average static electric field in the cluster - in collaboration with V. Strelkov (Russian Academy of Sciences) and U. Saalmann, J.M. Rost (MPI-PKS, Dresden, Germany)

V. Strelkov et al., Phys. Rev. Lett. 107, 113901 (2011)

Past Projects

Imaging of Fullerenes
We studied high-harmonic generation as a tool to image molecular structure on an ultrafast time scale. Theoretical predictions showed how the radius of a fullerene (C20 to C180) can be retrieved from the position of characteristic interference minima in the spectrum.
M.F. Ciappina et al., Phys. Rev. A 76, 063406 (2007); 78, 063405 (2008)