ASTRA, A Transition Density Matrix Approach to the Interaction of Attosecond Radiation with Atoms and Molecules (original) (raw)
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Attosecond-resolution quantum dynamics calculations for atoms and molecules in strong laser fields
Physical Review E, 2008
A parallel quantum electron and nuclei wave packet computer code, LZH-DICP, has been developed to study laser-atom-molecule interaction in the nonperturbative regime with attosecond resolution. The nonlinear phenomena occurring in that regime can be studied with the code in a rigorous way by numerically solving the time-dependent Schrödinger equation of electrons and nuclei. Time propagation of the wave functions is performed using a split-operator approach, and based on a sine discrete variable representation. Photoelectron spectra for hydrogen and kinetic-energy spectra for molecular hydrogen ion in linearly polarized laser fields are calculated using a flux operator scheme, which testifies to the validity and the high efficiency of LZH-DICP.
Frontiers in Optics 2013, 2013
The nonadiabatically coupled dynamics of electrons and nuclei is investigated for the ozone molecule on the attosecond time scale. A coherent superposition of nuclear wave packets located on different electronic states in the Chappuis and in the Hartley bands are created by pump pulses. The multiconfiguration time-dependent Hartree method is used to solve the coupled nuclear quantum dynamics in the framework of the adiabatic separation of the time-dependent Schrödinger equation including nonadiabatic couplings. Our nuclear wave-packet calculations demonstrate that the coherence between Hartley state B and one of the Chappuis states (Chappuis 1) is significantly large, while it is almost negligible for the other two cases (between Hartley B and Chappuis 2 or between Chappuis 1 and Chappuis 2). At present we limited our description of the electronic motion to the Franck-Condon region only due to the localization of the nuclear wave packets around this point during the first 5-6 fs.
Attosecond intramolecular electron dynamics
Xviiith International Conference on Ultrafast Phenomena, 2013
We present results of numerical simulations indicating a complex laser driven electron dynamics inside simple molecular systems on the attosecond time scale. This attosecond electron dynamics influences the instant of ionization of the molecule and the final electron momentum distributions.
Interaction of atomic and molecular systems with high-intensity ultraviolet radiation
Journal of the Optical Society of America B, 1984
The interaction of atomic and molecular species with picosecond ArF* laser radiation is studied at intensities up to 1015 W/cm 2. Anomalously strong, collision-free multiple ionization is observed. Standard theoretical models of stepwise ionization fail to describe the results. The experimental findings point to a collective response of the atom. At intensities of 1013 W/cm 2 , selective multiquantum excitation of autoionizing states in Kr, followed by stimulated emission at wavelengths as short as 91.6 and 93 nm, is observed. The 93-nm radiation is tunable over a 600-cm'1 interval, whereas the 91.6-nm frequency is fixed. among excited states.
General approach to few-cycle intense laser interactions with complex atoms
Physical Review A, 2007
A general ab-initio and non-perturbative method to solve the time-dependent Schrödinger equation (TDSE) for the interaction of a strong attosecond laser pulse with a general atom, i.e., beyond the models of quasi-one-electron or quasi-two-electron targets, is described. The field-free Hamiltonian and the dipole matrices are generated using a flexible B-spline R-matrix method. This numerical implementation enables us to construct term-dependent, non-orthogonal sets of one-electron orbitals for the bound and continuum electrons. The solution of the TDSE is propagated in time using the Arnoldi-Lanczos method, which does not require the diagonalization of any large matrices. The method is illustrated by an application to the multi-photon excitation and ionization of Ne atoms. Good agreement with R-matrix Floquet calculations for the generalized cross sections for two-photon ionization is achieved.
Computational methods for laser-atom interactions
Journal of Physics: Conference Series, 2007
We discuss a computational method to study the dynamics in the laser-atom interactions. There are two key ingredients to the new method. Firstly, we transform the differential time-dependent Schrödinger equation into a time-integral equation, in which the dynamics related wavefunction is separated from the background wavefunction analytically to improve the numerical accuracy. Secondly, we divide the space into an inner region and an outer region, and propagate the inner-region wavefunction in the full Hamiltonian numerically and outer-region wavefunction in the momentum space analytically. In this way, we remove the physical boundary in space. To show the effectiveness of the method, we simulate the carrierenvelop phase dependent high energy above-threshold-ionization yields, which are in good agreement with the experimental observations. Furthermore, we investigate the rescattering electron momentum spectra and provide an intuitive rescattering picture from a full quantum non-perturbative calculation.
Electron localization following attosecond molecular photoionization
Nature, 2010
For the past several decades, we have been able to directly probe the motion of atoms that is associated with chemical transformations and which occurs on the femtosecond (10 215 -s) timescale. However, studying the inner workings of atoms and molecules on the electronic timescale 1-4 has become possible only with the recent development of isolated attosecond (10 218 -s) laser pulses 5 . Such pulses have been used to investigate atomic photoexcitation and photoionization 6,7 and electron dynamics in solids 8 , and in molecules could help explore the prompt charge redistribution and localization that accompany photoexcitation processes. In recent work, the dissociative ionization of H 2 and D 2 was monitored on femtosecond timescales 9 and controlled using few-cycle near-infrared laser pulses 10 . Here we report a molecular attosecond pump-probe experiment based on that work: H 2 and D 2 are dissociatively ionized by a sequence comprising an isolated attosecond ultraviolet pulse and an intense few-cycle infrared pulse, and a localization of the electronic charge distribution within the molecule is measured that depends-with attosecond time resolution-on the delay between the pump and probe pulses. The localization occurs by means of two mechanisms, where the infrared laser influences the photoionization or the dissociation of the molecular ion. In the first case, charge localization arises from quantum mechanical interference involving autoionizing states and the laser-altered wavefunction of the departing electron. In the second case, charge localization arises owing to laser-driven population transfer between different electronic states of the molecular ion. These results establish attosecond pump-probe strategies as a powerful tool for investigating the complex molecular dynamics that result from the coupling between electronic and nuclear motions beyond the usual Born-Oppenheimer approximation.
Attosecond control in photoionization of hydrogen molecules
2011
We report experiments where hydrogen molecules were dissociatively ionized by an attosecond pulse train in the presence of a near-infrared field. Fragment ion yields from distinguishable ionization channels oscillate with a period that is half the optical cycle of the IR field. For molecules aligned parallel to the laser polarization axis, the oscillations are reproduced in two-electron quantum simulations, and can be explained in terms of an interference between ionization pathways that involve different harmonic orders and a laser-induced coupling between the 1s g and 2p u states of the molecular ion. This leads to a situation where the ionization probability is sensitive to the instantaneous polarization of the molecule by the IR electric field and demonstrates that we have probed the IR-induced electron dynamics with attosecond pulses.
Journal of Physical Chemistry A, 2001
The electronic excitation induced by ultrashort laser pulses and the subsequent photodissociation dynamics of molecular fluorine in an argon matrix are studied. The interactions of photofragments and host atoms are modeled using a diatomics-in-molecule Hamiltonian. Two types of methods are compared: (1) quantumclassical simulations where the nuclei are treated classically, with surface-hopping algorithms to describe either radiative or nonradiative transitions between different electronic states, and (2) fully quantum-mechanical simulations, but for a model system of reduced dimensionality, in which the two most essential degrees of freedom are considered. Some of the main results follow: (1) The sequential energy transfer events from the photoexcited F 2 into the lattice modes are such that the "reduced dimensionality" model is valid for the first 200 fs. This, in turn, allows us to use the quantum results to investigate the details of the excitation process with short laser pulses. Thus, it also serves as a reference for the quantum-classical "surface hopping" model of the excitation process. Moreover, it supports the validity of a laser pulse control strategy developed on the basis of the "reduced dimensionality" model. (2) In both the quantum and quantum-classical simulations, the separation of the F atoms following photodissociation does not exceed 20 bohr. The cage exit mechanisms appear qualitatively similar in the two sets of simulations, but quantum effects are quantitatively important.