Attosecond Time-Resolved Imaging of Molecular Structure by Photoelectron Holography
ABSTRACT Dynamic imaging of the molecular structure of H2+ is investigated by attosecond photoelectron holography. The interference between direct (reference) and backward rescattered (signal) photoelectrons in attosecond photoelectron holography reveals the birth time of both channels and the spatial information of molecular structure. This is confirmed by simulations with a semiclassical model and numerical solutions of the corresponding time-dependent Schrödinger equation, suggesting an attosecond time-resolved way of imaging molecular structure obtained from laser induced rescattering of ionized electrons. It is shown that both short and long rescattered electron trajectories can be imaged from the momentum distribution.
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ABSTRACT: We present a theoretical study of H2+ ionization under strong IR femtosecond pulses by using a method designed to extract correlated (2D) photoelectron and proton kinetic energy spectra. The results show two distinct ionization mechanisms—tunnel and multiphoton ionization—in which electrons and nuclei do not share the energy from the field in the same way. Electrons produced in multiphoton ionization share part of their energy with the nuclei, an effect that shows up in the 2D spectra in the form of energy-conservation fringes similar to those observed in weak-field ionization of diatomic molecules. In contrast, tunneling electrons lead to fringes whose position does not depend on the proton kinetic energy. At high intensity, the two processes coexist and the 2D plots show a very rich behavior, suggesting that the correlation between electron and nuclear dynamics in strong field ionization is more complex than one would have anticipated.Physical Review Letters 03/2013; 110(11). DOI:10.1103/PhysRevLett.110.113001 · 7.73 Impact Factor
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ABSTRACT: Tracing the motion of electrons has enormous relevance to understanding ubiquitous phenomena in ultrafast science, such as the dynamical evolution of the electron density during complex chemical and biological processes. Scattering of ultrashort x-ray pulses from an electronic wave packet would appear to be the most obvious approach to image the electronic motion in real time and real space with the notion that such scattering patterns, in the far-field regime, encode the instantaneous electron density of the wave packet. However, recent results by Dixit et al. [Proc. Natl. Acad. Sci. U.S.A. 109, 11 636 (2012)] have put this notion into question and have shown that the scattering in the far-field regime probes spatiotemporal density-density correlations. Here, we propose a possible way to image the instantaneous electron density of the wave packet via ultrafast x-ray phase contrast imaging. Moreover, we show that inelastic scattering processes, which plague ultrafast scattering in the far-field regime, do not contribute in ultrafast x-ray phase contrast imaging as a consequence of an interference effect. We illustrate our general findings by means of a wave packet that lies in the time and energy range of the dynamics of valence electrons in complex molecular and biological systems. This present work offers a potential to image not only instantaneous snapshots of nonstationary electron dynamics, but also the Laplacian of these snapshots which provide information about the complex bonding and topology of the charge distributions in the systems.Physical Review Letters 03/2013; 110(13):137403. DOI:10.1103/PhysRevLett.110.137403 · 7.73 Impact Factor
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ABSTRACT: We deploy a time-dependent Born–Oppenheimer approximation approach for numerically solving the time-dependent Schrödinger equation (TDSE) by reducing the wavefunction dimensionality to nuclear and electronic degrees of freedom, and apply it to a one-dimensional model of H2+. Based upon our three distinct error evaluation schemes, we quantitatively compare the wavefunctions and HHG spectra which are computed by the present approximation method, with those obtained by fully solving the TDSE. The similarities of both the wavefunctions and the HHG spectra justify that our approach is feasibly precise for medium laser intensity. It is also anticipated that this approximation can be adopted for other polyatomic molecules with a dimensionality reduction and computational simplification in calculating the time-dependent wavefunctions.Optics Communications 07/2013; 300:199–203. DOI:10.1016/j.optcom.2013.02.056 · 1.54 Impact Factor