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Author: Liu, C. ×

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    Mapping the Dissociative Ionization Dynamics of Molecular Nitrogen with Attosecond Time Resolution
    (College Park, Md. : APS, 2015) Trabattoni, A.; Klinker, M.; González-Vázquez, J.; Liu, C.; Sansone, G.; Linguerri, R.; Hochlaf, M.; Klei, J.; Vrakking, M. J. J.; Martín, F.; Nisoli, M.; Calegari, F.
    Studying the interaction of molecular nitrogen with extreme ultraviolet (XUV) radiation is of prime importance to understand radiation-induced processes occurring in Earth’s upper atmosphere. In particular, photoinduced dissociation dynamics involving excited states of N2+ leads to N and N+ atomic species that are relevant in atmospheric photochemical processes. However, tracking the relaxation dynamics of highly excited states of N2+ is difficult to achieve, and its theoretical modeling is notoriously complex. Here, we report on an experimental and theoretical investigation of the dissociation dynamics of N2+ induced by isolated attosecond XUV pulses in combination with few-optical-cycle near-infrared/visible (NIR/VIS) pulses. The momentum distribution of the produced N+ fragments is measured as a function of pump-probe delay with subfemtosecond resolution using a velocity map imaging spectrometer. The time-dependent measurements reveal the presence of NIR/VIS-induced transitions between N2+ states together with an interference pattern that carries the signature of the potential energy curves activated by the XUV pulse. We show that the subfemtosecond characterization of the interference pattern is essential for a semiquantitative determination of the repulsive part of these curves.
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    Mapping the dissociative ionization dynamics of molecular nitrogen with attosecond resolution
    (Bristol : IOP Publ., 2015) Klinker, M.; Trabattoni, A.; González-Vázquez, J.; Liu, C.; Sansone, G.; Linguerri, R.; Hochlaf, M..; Klei, J.; Vrakking, M.J.J.; Martin, F.; Nisoli, M.; Calegari, F.
    We wish to understand the processes underlying the ionization dynamics of N2 as experimentally induced and studied by recording the kinetic energy release (KER) in a XUV-pump/IR-probe setup. To this end a theoretical model was developed describing the ionization process using Dyson Orbitals and, subsequently, the dissociation process using a large set of diabatic potential energy surfaces (PES) on which to propagate. From said set of PES, a small subset is extracted allowing for the identification of one and two photon processes chiefly responsible for the experimentally observed features.
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    Characterizing time series: When Granger causality triggers complex networks
    (Bristol : Institute of Physics Publishing, 2012) Ge, T.; Cui, Y.; Lin, W.; Kurths, J.; Liu, C.
    In this paper, we propose a new approach to characterize time series with noise perturbations in both the time and frequency domains by combining Granger causality and complex networks. We construct directed and weighted complex networks from time series and use representative network measures to describe their physical and topological properties. Through analyzing the typical dynamical behaviors of some physical models and the MIT-BIH 7 human electrocardiogram data sets, we show that the proposed approach is able to capture and characterize various dynamics and has much potential for analyzing real-world time series of rather short length.