Article
TimeResolved Holography with Photoelectrons
FOM Institute AMOLF, Science Park 113, 1098 XG Amsterdam, Netherlands.
Science (Impact Factor: 33.61). 01/2011; 331(6013):614. DOI: 10.1126/science.1198450 Source: PubMed
ABSTRACT
Ionization is the dominant response of atoms and molecules to intense laser fields and is at the basis of several important techniques, such as the generation of attosecond pulses that allow the measurement of electron motion in real time. We present experiments in which metastable xenon atoms were ionized with intense 7micrometer laser pulses from a freeelectron laser. Holographic structures were observed that record underlying electron dynamics on a sublasercycle time scale, enabling photoelectron spectroscopy with a time resolution of almost two orders of magnitude higher than the duration of the ionizing pulse.

 "Longer wavelength also ensures more detailed analysis and interpretation of experimental and numerical results, based on (semi or quasi)classical (see, e.g., Refs. [5] [6] [7] [8]) and adiabatic [9] [10] theories. Circularly or nearcircularly polarized midIR pulses are ideal for precise attoclock measurements to elucidate tunneling dynamics [11] [12], and for obtaining the information of molecular orbital structure from the photoelectron momentum distribution perpendicular to the polarization plane [13]. "
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ABSTRACT: Aiming at efficient numerical treatment of tunneling ionization of atoms and molecules by midinfrared (IR) lasers, exterior time scaling (ETS) theory is formulated as a generalization of the timescaled coordinate approach. The key idea of ETS is the division of the spatial volume into a small region around the nucleus and its outside; the radial coordinates are time scaled only in the outer region. The continuum components of photoelectron wave packets are prevented from reaching the edge of the spatial simulation volume, enabling the longtime evolution of wave packets with a relatively small number of basis functions without concerns of electron reflections. On the other hand, the boundstate components are free from shrinking toward the origin because of nontime scaling in the inner region. Hence, the equations of motion in ETS are less stiff than the ones in the original timescaled coordinate approach in which the shrinking bound states make the equations of motion seriously stiff. For numerical implementation of ETS, the working equations are derived in terms of finiteelement discretevariablerepresentation functions. Furthermore, the stiffnessfree Lanczos time propagator is introduced to remove any persistent stiffness in the treatment of midIR lasers due to the involvement of hundreds of angularmomentum states. The test calculations for atomic hydrogen interacting with linearly polarized midIR pulses demonstrate the accuracy and numerical efficiency of the new scheme, and exhibit its special capability if there is no recollision with the parent ion. Hence, ETS will show its true potential for the detailed analysis of photoelectron wave packet dynamics in circularly or nearcircularly polarized midIR fields.  [Show abstract] [Hide abstract]
ABSTRACT: We study whether tunnel ionization of aligned molecules can be used to map out the electronic structure of the ionizing orbitals. We show that the common view, which associates tunnel ionization rates with the electronic density profile of the ionizing orbital, is not always correct. Using the example of tunnel ionization from the CO(2) molecule, we show how and why the angular structure of the alignmentdependent ionization rate moves with increasing the strength of the electric field. These modifications reflect a general trend for molecules.  [Show abstract] [Hide abstract]
ABSTRACT: The attosecond timescale electronic dynamics induced by an ultrashort laser pulse is computed using a multi configuration time dependent approach in ABCU (C(10)H(19)N), a medium size polyatomic molecule with a rigid cage geometry. The coupling between the electronic states induced by the strong pulse is included in the many electron Hamiltonian used to compute the electron dynamics. We show that it is possible to implement control of the electron density stereodynamics in this medium size molecule by varying the characteristics of the laser pulse, for example by polarizing the electric field either along the NC axis of the cage, or in the plane perpendicular to it. The excitation produces an oscillatory, nonstationary, electronic state that exhibits localization of the electron density in different parts of the molecule both during and after the pulse. The coherent oscillations of the nonstationary electronic state are also demonstrated through the alternation of the dipole moment of the molecule.
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