High Resolution Multiphoton Spectroscopy by a Tunable Free-Electron-Laser Light

Žitnik, M.; Mihelič, A.; Bučar, K.; Kavčič, M.; Rubensson, Jan‐Erik; Svanquist, M.; Söderström, Johan; Feifel, Raimund; Såthe, Conny; Ovcharenko, Yevheniy; Lyamayev, V.; Mazza, Tommaso; Meyer, Michael; Simon, M.; Journel, L.; Lüning, J.; Plekan, Oksana; Coreno, Marcello; Devetta, M.; Fraia, Michele Di; Finetti, P.; Richter, Robert; Grazioli, Cesare; Prince, Kevin C.; Callegari, Carlo

doi:10.1103/physrevlett.113.193201

Cited by 31 publications

(18 citation statements)

References 53 publications

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“…Conversely, once the model is parametrised, it can be used as a computationally inexpensive alternative to the numerical integration of the TDSE. This is for example the case of photoemission studies conducted with the long, coherent and intense XUV pulses that became recently available at seeded XFEL facilities [88][89][90].…”

Section: Discussionmentioning

confidence: 99%

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: Discussionmentioning

confidence: 99%

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

2016

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“…The real positive parameter η is varied until the expression for the ac Stark shift approaches an almost stationary value [52]. In contrast to what is observed when the reference Hamiltonian is regularized using exterior complex scaling (ECS) [53,54] instead of CAPs, due to the alteration of the wave functions in the complex-absorption region, the continuum-continuum matrix elements in Eq. (8) attain reasonably stationary values only for the narrowest resonances.…”

Section: Multielectron Ac Stark Shiftmentioning

confidence: 99%

Dressing effects in the attosecond transient absorption spectra of doubly excited states in helium

et al. 2015

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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 (ATAS) of helium dressed by a few-cycle visible pulse [C. Ott et al., Nature (London) 516, 374 (2014)] provide evidence of the inversion of Fano profiles. With the support of accurate ab initio calculations that reproduce the results of the latter experiment, here we investigate the new physics that arise from ATAS when the laser intensity is increased. In particular, we show that (i) previously unnoticed signatures of the dark 2p 2 1 S doubly excited state are observed in the experimental spectrum, (ii) inversion of Fano profiles is predicted to be periodic in the laser intensity, and (iii) the ac Stark shift of the higher terms in the sp + 2,n autoionizing series exceeds the ponderomotive energy, which is the result of a genuine two-electron contribution to the polarization of the excited atom.

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“…This includes finding the solution of the time-dependent Schrödinger equation in terms of the time-dependent amplitudes of the basis states from the restricted space [29][30][31], studying the dynamics in terms of the density matrix (e.g., see Refs. [32,33]), or solving a set of kinetic equations which describe the population of various atomic and ionic species during the interaction with the incident pulse [34,35]. The parameters which enter the model, such as autoionization widths, asymmetry parameters, photoionization cross sections, and Rabi frequencies, can be conveniently calculated using the ECS method.…”

Section: Photoionization Of An Atom In a Resonance Statementioning

confidence: 99%

Role of intermediate continuum states in exterior complex scaling calculations of two-photon ionization cross sections

Mihelič¹

2018

Phys. Rev. A

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The calculation of partial two-photon ionization cross sections in the above-threshold energy region is discussed in the framework of exterior complex scaling. It is shown that with a minor modification of the usual procedure, which is based on the calculation of the outgoing partial waves of the secondorder scattering wave function, reliable partial ionization amplitudes can be obtained. The modified procedure relies on a few-term least-squares fit of radial functions pertaining to different partial waves. To test the procedure, partial and total two-photon ionization cross sections of the helium atom have been calculated for a broad range of incident photon energies. The calculated cross sections may be seen to agree well with the results found in the literature. Furthermore, it is shown that, using a similar approach, partial photoionization cross sections of an atom in an autoionizing (resonance) state may be calculated in a relatively straightforward way. Such photoionization cross sections may find their use in enhanced few-parameter models describing the atom-light interaction in cases where a direct solution of the time-dependent Schrödinger equation becomes too resourceintensive.

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High Resolution Multiphoton Spectroscopy by a Tunable Free-Electron-Laser Light

Cited by 31 publications

References 53 publications

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

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

Dressing effects in the attosecond transient absorption spectra of doubly excited states in helium

Role of intermediate continuum states in exterior complex scaling calculations of two-photon ionization cross sections

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