Maximum Elliptical Dichroism in Atomic Two-Photon Ionization

Hofbrucker, J.; Volotka, A. V.; Fritzsche, S.

doi:10.1103/physrevlett.121.053401

Cited by 32 publications

(25 citation statements)

References 38 publications

(52 reference statements)

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“…the ground state, conventional anisotropy and asymmetry parameters fail to provide comprehensive tools for the analysis of photoionization from atomic superposition states. For example, the simplest case of a competition between one-and two-photon ionization processes can be analyzed using asymmetry parameters if the atom is prepared in the ground state [20][21][22][23][24][25][26][27] . In contrast, these analysis tools are either not applicable or do not provide a straightforward interpretation for the same processes if the atom is in the superposition of two states.…”

Section: Openmentioning

confidence: 99%

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Asymmetries in ionization of atomic superposition states by ultrashort laser pulses

Venzke

Becker

Jaroń-Becker

2020

Sci Rep

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Progress in ultrafast science allows for probing quantum superposition states with ultrashort laser pulses in the new regime where several linear and nonlinear ionization pathways compete. Interferences of pathways can be observed in the photoelectron angular distribution and in the past they have been analyzed for atoms and molecules in a single quantum state via anisotropy and asymmetry parameters. Those conventional parameters, however, do not provide comprehensive tools for probing superposition states in the emerging research area of bright and ultrashort light sources, such as free-electron lasers and high-order harmonic generation. We propose a new set of generalized asymmetry parameters which are sensitive to interference effects in the photoionization and the interplay of competing pathways as the laser pulse duration is shortened and the laser intensity is increased. The relevance of the parameters is demonstrated using results of state-of-the-art numerical solutions of the time-dependent Schrödinger equation for ionization of helium atom and neon atom.

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Section: Openmentioning

confidence: 99%

“…Probing atoms and molecules in their ground or excited states with ultrashort laser pulses opens a new regime where several linear and nonlinear ionization pathways compete and interfere [20][21][22][23][24][25][26][27] . For example, it has been shown how the competition between resonant and nonresonant pathways depends on the pulse width 20 .…”

mentioning

confidence: 99%

Asymmetries in ionization of atomic superposition states by ultrashort laser pulses

Venzke

Becker

Jaroń-Becker

2020

Sci Rep

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“…Various non-linear (second- as well as higher-order perturbation) processes have been observed during the past years but could often not be calculated in good detail for many ions, atoms or molecules of interest. Well-known second-order processes of this sort include, for instance, the multi-photon absorption and emission [ 1 , 2 , 3 ], the resonant [ 4 ] and two-photon ionization [ 5 , 6 ], the radiative and double Auger emission of atoms [ 7 , 8 ] and molecules [ 9 ], their (single-photon) double ionization [ 10 , 11 , 12 ] or the Rayleigh and Raman scattering of light [ 13 , 14 , 15 ], to name just a few. Until the present, however, most of these processes are not yet (well) understood quantitatively since, in perturbation theory, each additional order (beyond the first-order) typically requires an implicit summation (integration) over the full spectrum of the system.…”

Section: Introductionmentioning

confidence: 99%

Approximate Atomic Green Functions

Fritzsche

Surzhykov

2021

Molecules

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In atomic and many-particle physics, Green functions often occur as propagators to formally represent the (integration over the) complete spectrum of the underlying Hamiltonian. However, while these functions are very crucial to describing many second- and higher-order perturbation processes, they have hardly been considered and classified for complex atoms. Here, we show how relativistic (many-electron) Green functions can be approximated and systematically improved for few- and many-electron atoms and ions. The representation of these functions is based on classes of virtual excitations, or so-called excitation schemes, with regard to given bound-state reference configurations, and by applying a multi-configuration Dirac-Hartree-Fock expansion of all atomic states involved. A first implementation of these approximate Green functions has been realized in the framework of Jac, the Jena Atomic Calculator, and will facilitate the study of various multi-photon and/or multiple electron (emission) processes.

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“…The photoion in this case appears to be in an aligned state, which, in the case of inner-shell ionisation, is imprinted in the polarisation degree of subsequent fluorescence light 41 . As the nonlinear Cooper minima are a property of the fundamental two-(or generally multi-)photon ionisation process itself, they are expected to strongly influence many other observables such as photoelectron 42,43 or Auger electron polarisation, as well as their angular distributions.…”

Section: Introductionmentioning

confidence: 99%

Breakdown of the electric dipole approximation at Cooper minima in direct two-photon ionisation

Hofbrucker¹,

Volotka²,

Fritzsche³

2020

Sci Rep

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We predict breakdown of the electric dipole approximation at nonlinear Cooper minimum in direct two-photon K−shell atomic ionisation by circularly polarised light. According to predictions based on the electric dipole approximation, we expect that tuning the incident photon energy to the Cooper minimum in two-photon ionisation results in pure depletion of one spin projection of the initially bound 1s electrons, and hence, leaves the ionised atom in a fully oriented state. We show that by inclusion of electric quadrupole interaction, dramatic drop of orientation purity is obtained. The low degree of the remaining ion orientation provides a direct access to contributions of the electron-photon interaction beyond the electric dipole approximation in the two-photon ionisation of atoms and molecules. The orientation of the photoions can be experimentally detected either directly by a Stern-Gerlach analyzer, or by means of subsequent Kα fluorescence emission, which has the information about the ion orientation imprinted in the polarisation of the emitted photons. 2/113/11

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Maximum Elliptical Dichroism in Atomic Two-Photon Ionization

Cited by 32 publications

References 38 publications

Asymmetries in ionization of atomic superposition states by ultrashort laser pulses

Asymmetries in ionization of atomic superposition states by ultrashort laser pulses

Approximate Atomic Green Functions

Breakdown of the electric dipole approximation at Cooper minima in direct two-photon ionisation

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