Stimulated Raman scattering of an ultrashort XUV radiation pulse by a hydrogen atom

Mihai Dondera, Viorica Florescu, and Henri Bachau
Phys. Rev. A 95, 023417 – Published 22 February 2017

Abstract

We consider the hydrogen atom H(1s) exposed to an ultrashort laser pulse with a central frequency ω0 ranging from several hundreds of eV to 1.5 keV (55 a.u.) and a peak intensity of 3.51×1016W/cm2. We study the excitation of the atom by stimulated Raman scattering, a process involving pairs of frequencies (ω1,ω2). These frequencies are non-negligible components of the pulse Fourier transform and they satisfy the condition Eg+ω1=Eb+ω2,Eg and EbEn being the ground-state and the excited-state energy, respectively. The numerical results obtained by integrating the time-dependent Schrödinger equation (TDSE) are compared with calculations in lowest order perturbation theory (LOPT). In LOPT we consider, in the second order of PT, the contribution of the term A·P in the dipole approximation and, in first order of PT, the expression of A2 taken for first-order retardation effects. (A denotes the vector potential of the field and P is the momentum operator.) We focus on the Raman excitation of bound states with principal quantum numbers n up to n=13. The evaluation in perturbation theory of the A·P contribution to 1sns and 1snd transition probabilities uses analytic expressions of the corresponding Kramers–Heisenberg matrix elements. At fixed pulse duration τ=6π a.u. (0.48 fs), we find that the retardation effects play an important role at high frequencies: they progressively diminish as the frequency decreases until the contribution of A·P dominates over the A2 contribution for ω0 values of a few a.u. We also study the dependence of the Raman process on the pulse duration for several values of ω0. In the case ω0=13a.u.(354eV) where dipole and nondipole contributions are of the same order of magnitude, we present the Raman excitation probability as a function of the pulse duration for excited ns,np, and nd states.

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  • Received 19 October 2016

DOI:https://doi.org/10.1103/PhysRevA.95.023417

©2017 American Physical Society

Physics Subject Headings (PhySH)

Atomic, Molecular & Optical

Authors & Affiliations

Mihai Dondera* and Viorica Florescu

  • Department of Physics and Centre for Advanced Quantum Physics, University of Bucharest, MG-11, Bucharest-Măgurele, 077125, Romania

Henri Bachau

  • Centre des Lasers Intenses et Applications, Université de Bordeaux-CNRS-CEA, 33405 Talence Cedex, France

  • *don@barutu.fizica.unibuc.ro
  • flor@barutu.fizica.unibuc.ro
  • henri.bachau@u-bordeaux.fr

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Issue

Vol. 95, Iss. 2 — February 2017

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