23 research outputs found
Time-dependent configuration-interaction-singles calculation of the -subshell two-photon ionization cross section in xenon
The two-photon ionization cross section of xenon in the photon-energy
range below the one-photon ionization threshold is calculated within the
time-dependent configuration-interaction-singles (TDCIS) method. The TDCIS
calculations are compared to random-phase-approximation (RPA) calculations
[Wendin \textit{et al.}, J. Opt. Soc. Am. B \textbf{4}, 833 (1987)] and are
found to reproduce the energy positions of the intermediate Rydberg states
reasonably well. The effect of interchannel coupling is also investigated and
found to change the cross section of the shell only slightly compared to
the intrachannel case.Comment: 11 pages, 3 figure
Wave-packet propagation based calculation of above-threshold ionization in the x-ray regime
We investigate the multi-photon process of above-threshold ionization for the
light elements hydrogen, carbon, nitrogen and oxygen in the hard x-ray regime.
Numerical challenges are discussed and by comparing Hartree-Fock-Slater
calculations to configuration-interaction-singles results we justify the
mean-field potential approach in this regime. We present a theoretical
prediction of two-photon above-threshold-ionization cross sections for the
mentioned elements. Moreover, we study how the importance of above-threshold
ionization varies with intensity. We find that for carbon, at x-ray intensities
around , two-photon above-threshold ionization of the
K-shell electrons is as probable as one-photon ionization of the L-shell
electrons.Comment: 13 pages, 4 figures, 1 tabl
Application of the Maupertuis Principle to quantum mechanics
In its geometric form, the Maupertuis Principle states that the movement of a
classical particle in an external potential V(x) can be understood as a free
movement in a curved space with the metric gμν(x) = 2M[V(x) - E]δμν. We extend
this principle to the quantum regime by showing that the wavefunction of the
particle is governed by a Schrödinger equation of a free particle moving
through curved space. The kinetic operator is the Weyl-invariant
Laplace–Beltrami operator. On the basis of this observation, we calculate the
semiclassical expansion of the particle density
Theoretical characterization of the collective resonance states underlying the xenon giant dipole resonance
We present a detailed theoretical characterization of the two fundamental
collective resonances underlying the xenon giant dipole resonance (GDR). This
is achieved consistently by two complementary methods implemented within the
framework of the configuration-interaction singles (CIS) theory. The first
method accesses the resonance states by diagonalizing the many-electron
Hamiltonian using the smooth exterior complex scaling technique. The second
method involves a new application of the Gabor analysis to wave-packet
dynamics. We identify one resonance at an excitation energy of 74 eV with a
lifetime of 27 as, and the second at 107 eV with a lifetime of 11 as. Our work
provides a deeper understanding of the nature of the resonances associated with
the GDR: a group of close-lying intrachannel resonances splits into two
far-separated resonances through interchannel couplings involving the 4d
electrons. The CIS approach allows a transparent interpretation of the two
resonances as new collective modes. Due to the strong entanglement between the
excited electron and the ionic core, the resonance wave functions are not
dominated by any single particle-hole state. This gives rise to plasma-like
collective oscillations of the 4d shell as a whole.Comment: 12 pages, 6 figures, 2 table
Quantum optimal control of photoelectron spectra and angular distributions
Photoelectron spectra and photoelectron angular distributions obtained in
photoionization reveal important information on e.g. charge transfer or hole
coherence in the parent ion. Here we show that optimal control of the
underlying quantum dynamics can be used to enhance desired features in the
photoelectron spectra and angular distributions. To this end, we combine
Krotov's method for optimal control theory with the time-dependent
configuration interaction singles formalism and a splitting approach to
calculate photoelectron spectra and angular distributions. The optimization
target can account for specific desired properties in the photoelectron angular
distribution alone, in the photoelectron spectrum, or in both. We demonstrate
the method for hydrogen and then apply it to argon under strong XUV radiation,
maximizing the difference of emission into the upper and lower hemispheres, in
order to realize directed electron emission in the XUV regime
Suppression of hole decoherence in ultrafast photoionization
In simple one-photon ionization, decoherence occurs due to entanglement between ion and photoelectron. Therefore, the preparation of coherent superpositions of electronic eigenstates of the hole in the photoion is extremely difficult. We demonstrate for the xenon atom that the degree of electronic coherence of the photoion in attosecond photoionization can be enhanced if the influence of many-body interactions is properly controlled. A mechanism at low photon energies involving multiphoton ionization is found, suppressing the loss of coherence through ionization into the same photoelectron partial waves. The degree of coherence found between the 4 d0 and 5 s hole states is, on the one hand, limited by Auger decay of the 4 d0 hole. On the other hand, increasing the population ratio such that a significant portion of the state is in a true superposition of both states renders the maximization of the degree of coherence difficult
Theoretical characterization of the collective resonance states underlying the xenon giant dipole resonance
Nonlinear effects in photoionization over a broad photon-energy range within the TDCIS scheme
The present tutorial provides an overview of the time-dependent configuration interaction singles scheme applied to nonlinear ionization over a broad photon-energy range. The efficient propagation of the wave function and the calculation of photoelectron spectra within this approach are described and demonstrated in various applications. Above-threshold ionization of argon and xenon in the extreme ultraviolet energy range is investigated as an example. A particular focus is put on the xenon 4d giant dipole resonance and the information that nonlinear ionization can provide about resonance substructure. Furthermore, above-threshold ionization is studied in the x-ray regime and the intensity regime, at which multiphoton ionization starts to play a role at hard x-ray photon energies, is identified