He photoionization: β N and σ N below N = 5 and 6 thresholds

Argenti, Luca; Moccia, R.

doi:10.1007/s00214-007-0369-4

Cited by 12 publications

(9 citation statements)

References 28 publications

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“…To determine the values of these parameters, and to subsequently verify the prediction of the model against reliable benchmarks, we carried out accurate ab initio simulations based on the numerical solution of the time-dependent Schrödinger equation [10,[32][33][34] where the wave function for the two-active-electron system is represented in a B-spline [72,73] bipolar-sphericalharmonics [74] close-coupling basis [75][76][77][78], for both the time propagation and the asymptotic analysis of the single-ionization wave packet [32,79,80], while the timestep propagation is carried out with a Krylov unitary one-photon photoelectron spectrum obtained with using the XUV APT alone. The first spectrum (a) was used to determine the global scaling factor C, while spectra like the one in (b) were used to confirm the parameters of the two 1 P o autoionizing state.…”

Section: Resonant Rabitt Spectrum Of Heliummentioning

confidence: 99%

“…To determine the values of these parameters, and to subsequently verify the prediction of the model against reliable benchmarks, we carried out accurate ab initio simulations based on the numerical solution of the time-dependent Schrödinger equation [10,[32][33][34] where the wave function for the two-active-electron system is represented in a B-spline [72,73] bipolar-sphericalharmonics [74] close-coupling basis [75][76][77][78], for both the time propagation and the asymptotic analysis of the single-ionization wave packet [32,79,80], while the timestep propagation is carried out with a Krylov unitary approximation [81] to a second-order split exponential time-evolution operator in velocity gauge, and implemented in a parallel code which makes use of the PETSc numerical library [82][83][84]. In the simulations, both the XUV APT and the IR probe have a duration (fwhm) of 6 fs, while their peak intensity is I XUV = 5 GW/cm 2 and I IR = 10 GW/cm 2 , respectively.…”

Section: Resonant Rabitt Spectrum Of Heliummentioning

confidence: 99%

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Two-photon finite-pulse model for resonant transitions in attosecond experiments

2016

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We present an analytical model capable of describing two-photon ionization of atoms with attosecond pulses in the presence of intermediate and final isolated autoionizing states. The model is based on the finite-pulse formulation of second-order time-dependent perturbation theory. It approximates the intermediate and final states with Fano's theory for resonant continua, and it depends on a small set of atomic parameters that can either be obtained from separate ab initio calculations or be extracted from a few selected experiments. We use the model to compute the two-photon resonant photoelectron spectrum of helium below the N = 2 threshold for the RABITT (reconstruction of attosecond beating by interference of two-photon transitions) pump-probe scheme, in which an XUV attosecond pulse train is used in association with a weak IR probe, obtaining results in quantitative agreement with those from accurate ab initio simulations. In particular, we show that (i) the use of finite pulses results in a homogeneous redshift of the RABITT beating frequency, as well as a resonant modulation of the beating frequency in proximity to intermediate autoionizing states; (ii) the phase of resonant two-photon amplitudes generally experiences a continuous excursion as a function of the intermediate detuning, with either zero or 2π overall variation.

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Section: Resonant Rabitt Spectrum Of Heliummentioning

confidence: 99%

“…To determine the values of these parameters, and to subsequently verify the prediction of the model against reliable benchmarks, we carried out accurate ab initio simulations based on the numerical solution of the time-dependent Schrödinger equation [10,[32][33][34] where the wave function for the two-active-electron system is represented in a B-spline [72,73] bipolar-sphericalharmonics [74] close-coupling basis [75][76][77][78], for both the time propagation and the asymptotic analysis of the single-ionization wave packet [32,79,80], while the timestep propagation is carried out with a Krylov unitary approximation [81] to a second-order split exponential time-evolution operator in velocity gauge, and implemented in a parallel code which makes use of the PETSc numerical library [82][83][84]. In the simulations, both the XUV APT and the IR probe have a duration (fwhm) of 6 fs, while their peak intensity is I XUV = 5 GW/cm 2 and I IR = 10 GW/cm 2 , respectively.…”

Section: Resonant Rabitt Spectrum Of Heliummentioning

confidence: 99%

Two-photon finite-pulse model for resonant transitions in attosecond experiments

2016

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“…In the present work, the single-ionization scattering states of helium below the double ionization threshold are computed using the B-spline K-matrix method [61,62]. The K-matrix method is an L 2 realization of a configurationinteraction calculation in the continuum that has been successfully applied to a number of problems in atomic and molecular physics [42,53,[63][64][65][66][67][68][69][70]. This method will be briefly summarized below in the case of helium, for scattering states with total symmetry Γ, which we will not explicitly indicate, for brevity.…”

Section: Theorymentioning

confidence: 99%

Attosecond Transient Absorption Spectroscopy of doubly-excited states in helium

Argenti

Ott

Pfeifer

et al. 2014

J. Phys.: Conf. Ser.

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Strong-field manipulation of autoionizing states is a crucial aspect of electronic quantum control. Recent measurements of the attosecond transient absorption spectrum of helium dressed by a fewcycle visible pulse [Ott et al., arXiv:1205.0519[physics.atom-ph] ] provide evidence of novel ultrafast resonant phenomena, namely, two-photon Rabi oscillations between doubly-excited states and the inversion of Fano profiles. Here we present the results of accurate ab-initio calculations that agree with these observations and in addition predict that (i) inversion of Fano profiles is actually periodic in the coupling laser intensity and (ii) the supposedly dark 2p 2 1 S state also appears in the spectrum. Closer inspection of the experimental data confirms the latter prediction.

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“…, is a scattering state in which the parent ion and the photoelectron are not angularly or spin coupled, which fulfills incoming boundary conditions, and in which the photoelectron has a well defined propagation direction Ω [25,53,54]. We can now use the partitioning of the wavefunction in a last short-range component and many long-range components,…”

Section: Theoretical Methodsmentioning

confidence: 99%

Ionic Coherence in Resonant Above-Threshold Attosecond Ionization Spectroscopy

Mehmood¹,

Lindroth²,

Argenti³

2022

Preprint

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The ionization of atoms with sequences of attosecond pulses gives rise to excited ionic states that are entangled with the emitted photoelectron. Still, the ionic ensemble preserves some coherence that can be controlled through the laser parameters. In helium, control of the 2s/2p He + coherence is mediated by the autoionizing states below the N = 2 threshold [Phys. Rev. Res. 3, 023233 (2021)]. In the present work we study the role of the resonances both below and above the N = 3 threshold on the coherence of the N = 3 He + ion, in the attosecond pump-probe ionization of the helium atom, which we simulate using the newstock ab initio code. Due to the fine-structure splitting of the N=3 He + level, the ionic dipole beats on a picosecond timescale. We show how, from the dipole beating, it is possible to reconstruct the polarization of the ion at its inception.

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He photoionization: β N and σ N below N = 5 and 6 thresholds

Cited by 12 publications

References 28 publications

Two-photon finite-pulse model for resonant transitions in attosecond experiments

Two-photon finite-pulse model for resonant transitions in attosecond experiments

Attosecond Transient Absorption Spectroscopy of doubly-excited states in helium

Ionic Coherence in Resonant Above-Threshold Attosecond Ionization Spectroscopy

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