Excitation of helium Rydberg states and doubly excited resonances in strong extreme ultraviolet fields: Full-dimensional quantum dynamics using exponentially tempered Gaussian basis sets

Abstract

Recently optimized exponentially tempered Gaussian basis sets [P. R. Kapralova-Zdanska and J. Smydke, J. Chem. Phys. 138, 024105 (2013)] are employed in quantitative simulations of helium absorption cross-sections and two-photon excitation yields of doubly excited resonances. Linearly polarized half-infinite and Gaussian laser pulses at wavelengths 38-58 nm and large intensities up to 100 TW/cm(2) are considered. The emphasis is laid on convergence of the results with respect to the quality of the Gaussian basis sets (typically limited by a number of partial waves, density, and spatial extent of the basis functions) as well as to the quality of the basis set of field-free states (typically limited by the maximum rotational quantum number and maximum excitation of the lower electron). Particular attention is paid to stability of the results with respect to varying complex scaling parameter. Moreover, the study of the dynamics is preceded by a thorough check of helium energies and oscillator strengths as they are obtained with the exponentially tempered Gaussian basis sets, being also compared with yet unpublished emission wavelengths measured in electric discharge experiments.

Photoionization of few electron systems: a hybrid coupled channels approach

“…The positions of the resonances are accurate on the level of 10 −3 a.u. in energy [27], showing that the correlated states are well represented by the method. Here we had chosen a box size of 45 a.u.…”

“…The single photon peak of the 1s channel is computed to a few percent accuracy, except for a feature around 1.3 a.u., with a single ionic state. The resonant feature can be identified with the 2s2p doubly excited state [27], which is reproduced to few percent accuracy with the addition of 2nd shell ionic states. While the position of the resonance is reproduced accurately in the calculations presented here, the propagation time was well below the life-time of this resonance which is reflected in the width of the feature that is well above the natural line width.…”

“…For obtaining the resonances with tSURFF, one can simply propagate until the resonance has decayed completely and all flux has passed through the surface where the flux is collected. At this point it should be remarked that the relevant information about resonances may be generated more efficiently by stationary methods like time-independent complex scaling [27,28]. As the comparison in figure 1 is with the two-electron code where long propagation times become rather costly, we compare the spectra at time T = 60 laser cycles, where the resonances have not emerged yet.…”

Ab-initio theory of photoionization via resonances

“…We demonstrate the predictions of our theory for helium using ab-initio electronic-structure data from Ref. 14,15. By using advanced non-Hermitian quantum-chemistry algorithms 16,17 , our theory can also be applied for larger atoms and molecules.…”

“…al. 14 , and are used in all the calculations in the main text. For copmarison, we show additional ab-initio results from Ref.…”