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Author: Ivanov, M. ×

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    Molecular Auger Interferometry
    (Bristol : IOP Publ., 2020) Khokhlova, M.; Cooper, B.; Ueda, K.; Prince, K.C.; Kolorenč, P.; Ivanov, M.; Averbukh, V.
    We propose a theory of interferometric measurement of a normal Auger decay width in molecules. Molecular Auger interferometry is based on the coherent phase control of Auger dynamics in a two-colour (ω/2ω) laser field. We show that, in contrast to atoms, in oriented molecules of certain point groups (e.g. CH3F) the relative ω/2ω phase modulates the total ionisation yield. A simple analytical formula is derived for the extraction of the widths of Auger-active states from a molecular Auger interferogram, avoiding the need of either attosecond or high-resolution spectroscopy.
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    X-ray imaging of chemically active valence electrons during a pericyclic reaction
    (London : Nature Publishing Group, 2014) Bredtmann, T.; Ivanov, M.; Dixit, G.
    Time-resolved imaging of chemically active valence electron densities is a long-sought goal, as these electrons dictate the course of chemical reactions. However, X-ray scattering is always dominated by the core and inert valence electrons, making time-resolved X-ray imaging of chemically active valence electron densities extremely challenging. Here we demonstrate an effective and robust method, which emphasizes the information encoded in weakly scattered photons, to image chemically active valence electron densities. The degenerate Cope rearrangement of semibullvalene, a pericyclic reaction, is used as an example to visually illustrate our approach. Our work also provides experimental access to the long-standing problem of synchronous versus asynchronous bond formation and breaking during pericyclic reactions.
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    The role of the Kramers-Henneberger atom in the higher-order Kerr effect
    (Bristol : IOP, 2013) Richter, M.; Patchkovskii, S.; Morales, F.; Smirnova, O.; Ivanov, M.
    We discuss the connection between strong-field ionization, saturation of the Kerr response and the formation of the Kramers-Henneberger (KH) atom and long-living excitations in intense infrared (IR) external fields. We present a generalized model for the intensity-dependent response of atoms in strong IR laser fields, describing deviations in the nonlinear response at the frequency of the driving field from the standard model. We show that shaping the driving laser pulse allows one to reveal signatures of the excited KH states in the Kerr response of an individual atom.
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    Even harmonic generation in isotropic media of dissociating homonuclear molecules
    ([London] : Macmillan Publishers Limited, part of Springer Nature, 2016) Silva, R.E.F.; Rivière, P.; Morales, F.; Smirnova, O.; Ivanov, M.; Martín, F.
    Isotropic gases irradiated by long pulses of intense IR light can generate very high harmonics of the incident field. It is generally accepted that, due to the symmetry of the generating medium, be it an atomic or an isotropic molecular gas, only odd harmonics of the driving field can be produced. Here we show how the interplay of electronic and nuclear dynamics can lead to a marked breakdown of this standard picture: a substantial part of the harmonic spectrum can consist of even rather than odd harmonics. We demonstrate the effect using ab-initio solutions of the time-dependent Schrödinger equation for and its isotopes in full dimensionality. By means of a simple analytical model, we identify its physical origin, which is the appearance of a permanent dipole moment in dissociating homonuclear molecules, caused by light-induced localization of the electric charge during dissociation. The effect arises for sufficiently long laser pulses and the region of the spectrum where even harmonics are produced is controlled by pulse duration. Our results (i) show how the interplay of femtosecond nuclear and attosecond electronic dynamics, which affects the charge flow inside the dissociating molecule, is reflected in the nonlinear response, and (ii) force one to augment standard selection rules found in nonlinear optics textbooks by considering light-induced modifications of the medium during the generation process.