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Autoionization of very-high-n strontium Rydberg states

G. Fields, X. Zhang, F. B. Dunning, S. Yoshida, and J. Burgdörfer
Phys. Rev. A 97, 013429 – Published 31 January 2018
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  • INTRODUCTION
  • EXPERIMENTAL APPROACH
  • THEORY
  • ZERO-FIELD AUTOIONIZATION RATES
  • WAVE-PACKET DYNAMICS IN ELECTRIC FIELDS
  • CONCLUSIONS AND OUTLOOK
  • ACKNOWLEDGMENTS
    • References

    Abstract

    We study, using a combination of experiment and theory, the excitation and decay of very-high-n(n∼280–430) strontium autoionizing Rydberg states formed by near-resonant driving of the 5sS1/22→5pP1/22 core-ion transition. The branching ratio between decay through radiative transitions and through autoionization is explored. Autoionization rates are measured as a function of both the n and ℓ quantum numbers of the Rydberg electron. The nonstationary decay dynamics is studied by creating and manipulating Rydberg wave packets and by varying the laser pulse that drives the core excitation.

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    • Received 29 September 2017

    DOI:https://doi.org/10.1103/PhysRevA.97.013429

    ©2018 American Physical Society

    Physics Subject Headings (PhySH)

    1. Research Areas
    Autoionization & Auger processesLifetimes & widthsSingle- and few-photon ionization & excitationSpontaneous emissionStark effect
    Atomic, Molecular & Optical

    Authors & Affiliations

    G. Fields1, X. Zhang1, F. B. Dunning1, S. Yoshida2, and J. Burgdörfer2

    • 1Department of Physics and Astronomy, Rice University, Houston, Texas 77005-1892, USA
    • 2Institute for Theoretical Physics, Vienna University of Technology, Vienna A-1040, Austria, European Union

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    Vol. 97, Iss. 1 — January 2018

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    Images

    • Figure 1
      Figure 1

      Energy-level diagram for autoionization and radiative decay of doubly excited Rydberg states of strontium. Initially, the ground-state atom is excited to a singly excited Rydberg state, 5snℓLJ1, in the singlet sector by three-photon excitation (indicated by a sequence of three arrows). The subsequent core excitation of the other valence electron yields doubly excited states, 5p1/2nℓj (a single solid arrow). They autoionize (open arrows) or decay radiatively (dashed arrows) to singly excited states, 5snℓLJ2S+1, or to doubly excited states, 4d3/2nℓj. Each shaded area represents the continuum states associated with an ionization threshold corresponding to the indicated energy level of the Sr+ core ion. The subspace spanning the basis of the master equation [Eq. (6)] is indicated by the light-blue box.

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    • Figure 2
      Figure 2

      Schematic diagram of the apparatus. The inset shows the three-photon excitation scheme employed.

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    • Figure 3
      Figure 3

      (a) Calculated complex eigenenergies between the 4d2D and the 5p2P ionization thresholds. Yellow (light gray) dots: extended continuum states; green (gray) dots: 5pj1npj2 autoionizing resonances; red (black) dots: 5pj1nfj2 autoionizing resonances. The top frame shows a blow-up of the region near the 5p2P threshold. (b) Autoionization lifetimes of the 5p1/2nℓj eigenstates as a function of effective quantum number neff.

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    • Figure 4
      Figure 4

      Measured (dots) and calculated (line) Rydberg atom loss spectra for (a) the 387P11 and (b) 384F31 states as the 422 nm autoionizing laser is scanned across the 5sS1/22→5pP1/22 core-ion transition. The duration of the 422 nm laser pulse is 140 ns. The calculated excitation spectra at the end of the core-excitation pulse starting from (c) the 5s5pP11 state and (d) the 5s5fF31 state. While the excitation spectra [(c),(d)] are time dependent, the surviving Rydberg populations [(a),(b)] are evaluated in the stationary limit after all doubly excited states have decayed radiatively or via autoionization.

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    • Figure 5
      Figure 5

      Measured (filled symbols) and calculated (open symbols) widths of (a) 5p1/2npj and (b) 5p1/2nfj autoionization features as a function of 1/neff3. For 5snpP1, the data are fitted separately for the measured (solid line) and the simulated (dashed line) results, while a single linear fit is performed for 5snfF1. The extrapolation neff−3→0 provides an estimate for the radiative decay rate of the isolated core ion.

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    • Figure 6
      Figure 6

      Measured (filled symbols) and calculated (open symbols) detuning of the 5sS1/22→5p2P3/2 core-ion transition as a function of 1/neff3. The dashed lines show linear fits to the data.

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    • Figure 7
      Figure 7

      Rydberg atom loss spectrum for the 5s320pP11 state obtained using a high 422 nm (core-exciting) laser power (∼8 mW) and a 500-ns-long excitation pulse. For reference, the upper scale indicates the positions of neighboring nP states.

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    • Figure 8
      Figure 8

      Number of surviving Rydberg atoms as a function of the duration of the 422 nm core-exciting laser pulse for the (average) laser powers indicated. The symbols and the lines are the measured data and the simulated results, respectively. The initial state is 5s320pP11.

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    • Figure 9
      Figure 9

      (a) Calculated L distribution as a function of pump-pulse duration Tp when the initial 5s320pP11(MJ=1) state is subject to a pump pulse with a field strength of 1.8mVcm−1 (see text). (b) Measured fraction of 5s320pP11 Rydberg atoms that survives as a function of the duration of the pump pulse (see text) for the 422 nm core-excitation laser powers indicated. The 422 nm laser pulse is 100 ns long. (c) Calculated autoionization rates for L=1, L=3, and L>3 weighted by the L-state population in (a) as a function of pump-pulse duration Tp.

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    • Figure 10
      Figure 10

      Left column: Excitation spectra for “5s310fF31” initial states recorded using identical laser powers in the presence of the dc fields indicated (note the change in scale of the vertical axis). The positions of the vertical lines represent the energy of the field-dressed “5s310fF31” state and its height represents the overlap between the field-dressed and the field-free 5s310fF31 states. Right column: Rydberg atom autoionization loss spectra recorded with the Rydberg excitation lasers tuned to the points indicated by the lines in the corresponding excitation spectra.

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