EUV two-photon-ionization cross sections of helium from the solution of the time-dependent Schrödinger equation, and comparison with measurements using free-electron lasers

EUV two-photon-ionization cross sections of helium from the solution of the time-dependent Schrödinger equation, and comparison with measurements using free-electron lasers

Νικολαΐδης, Κλεάνθης A.

Κομνηνός, Γιάννης

Μερκούρης, Θεόδωρος Δ.

Άρθρο σε επιστημονικό περιοδικό

2016

Two recent experimental papers reported the first measurements of absolute two-photon-ionization cross sections σ(2) of helium, for EUV wavelengths, using free-electron laser (FEL) pulses [Sato, J. Phys. B 44, 161001 (2011)10.1088/0953-4075/44/16/161001; Fushitani, Phys. Rev. A 88, 063422 (2013)10.1103/PhysRevA.88.063422]. The wavelengths correspond to transitions that are off resonance as well as on resonance with the 1s2p and 1s3p1Po Rydberg states. Inspection of their results reveals considerable discrepancies, while their comparison with theoretical results obtained earlier from time-independent calculations, one perturbative and two nonperturbative ones, cannot lead to secure conclusions as to the true values of σ(2). We examined this prototypical problem by implementing a time-dependent approach, which utilizes the nonperturbative solution of the time-dependent Schrödinger equation. This solution was obtained in terms of the state-specific expansion approach, in an upgraded version where the coupling matrix elements are computed using the full electric operator of the multipolar Hamiltonian. The σ(2) were obtained for pulses of 300 fs, as in the 2011 FEL experiment. Their computation was achieved by fitting the time-dependent ionization survival probability to e-Γt, where Γ is the rate of ionization. The wavelengths and intensities are those of the FEL experiments, as well as others, such as the wavelengths 52.22 and 51.56 nm, for which the 1s4p1Po and 1s5p1Po levels are on resonance with the initial S1 state. Apart from the predictions for these wavelengths, the paper contains characteristic comparisons among all the results on these EUV σ(2), experimental and theoretical. In general, the trends predicted by nonperturbative methods are confirmed by the FEL measurements. However, discrepancies exist among the absolute numbers. Furthermore, comparison among the results of the three nonperturbative approaches (present time-dependent and two earlier time-independent ones published in 1999 and 2005) indicates an overall consistency, although quantitative differences for individual cases are apparent.

Φυσική και θεωρητική χημεία (EL)

Ατομική φυσική (συμπ. μοριακή φυσική, σχετικότητα, κβαντική θεωρία και φυσική στερεάς κατάστασης) (EL)

Atomic physics (Incl. molecular physics, relativity, quantum theory, and solid state physics) (EN)

Physical and theoretical chemistry (EN)

English

American Physical Society

Physical Review A

© 2016 American Physical Society.

© 2016 American Physical Society. (EN)

Εθνικό Ίδρυμα Ερευνών (ΕΙΕ)

Ήλιος - Αποθετήριο Εθνικού Ιδρύματος Ερευνών