Symmetry Breaking and Strong Persistent Plasma Currents via Resonant Destabilization of Atoms

C. Brée, M. Hofmann, A. Demircan, U. Morgner, O. Kosareva, A. Savel’ev, A. Husakou, M. Ivanov, and I. Babushkin

Phys. Rev. Lett. 119, 243202 – Published 13 December 2017

Abstract

The ionization rate of an atom in a strong optical field can be resonantly enhanced by the presence of long-living atomic levels (so-called Freeman resonances). This process is most prominent in the multiphoton ionization regime, meaning that the ionization event takes many optical cycles. Nevertheless, here, we show that these resonances can lead to rapid subcycle-scale plasma buildup at the resonant values of the intensity in the pump pulse. The fast buildup can break the cycle-to-cycle symmetry of the ionization process, resulting in the generation of persistent macroscopic plasma currents which remain after the end of the pulse. This, in turn, gives rise to a broadband radiation of unusual spectral structure, forming a comb from terahertz to visible. This radiation contains fingerprints of the attosecond electron dynamics in Rydberg states during ionization.

Received 3 August 2017

DOI:https://doi.org/10.1103/PhysRevLett.119.243202

Physics Subject Headings (PhySH)

Electronic transitions Multiphoton or tunneling ionization & excitation Photoemission Strong electromagnetic field effects Strong field ionization & excitation Ultrafast optics Ultrafast phenomena

Atomic, Molecular & Optical

Authors & Affiliations

C. Brée¹, M. Hofmann², A. Demircan^3,4, U. Morgner^3,4, O. Kosareva⁵, A. Savel’ev⁵, A. Husakou⁶, M. Ivanov⁶, and I. Babushkin^3,6

¹Weierstrass Institute, Mohrenstrasse 39, 10117 Berlin, Germany
²Virtimo AG, Münzstrasse 5, 10178 Berlin, Germany
³Institute for Quantum Optics, Leibniz Universität Hannover, Welfengarten 1, 30167 Hannover, Germany
⁴Hannover Centre for optical Technologies, Nienburger Strasse 17, 30167 Hannover, Germany
⁵Physics Faculty, Lomonosov Moscow State University, Leninskie gory 1-62, 119991 Moscow, Russia
⁶Max Born Institute, Max Born Strasse 2a, 12489 Berlin, Germany

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Issue

Vol. 119, Iss. 24 — 15 December 2017

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Images

Figure 1
(a) Ionization rate in dependence of the pump intensity; peaks in ionization rate are Freeman resonances. (b) Intensity (red curve) and the corresponding ionization rate (blue curve) generated by a long pulse of the form described in text, with the wavelength 800 nm, duration 240 fs and peak intensity $17 TW / {cm}^{2}$ . (c), (d) Macroscopic free electron current for $17 TW / {cm}^{2}$ (c) and $23 TW / {cm}^{2}$ (d); other parameters as in (b); For the case of $17 TW / {cm}^{2}$ a persistent current after the field passage is visible. (e) The spectra of the corresponding radiation $E_{f}$ given by Eq. (2) for the currents shown in (c).
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Figure 2
The generated radiation and its spectrum in dependence on the pulse intensity for the parameters of Fig. 1, assuming the adiabatic procedure as well as the direct solution of the TDSE. (a), (b) Fraction of ionized electrons $ρ / ρ_{0}$ (red curves) and the low frequency energy (integrated from 0 to 100 THz) (blue curves) for the case of adiabatic theory (a) and by direct solution of the TDSE (b). (c), (d) Corresponding spectra in dependence of intensity for the adiabatic theory (c) and by direct solution of the TDSE (d).
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Figure 3
Comparison of the solution of the TDSE with the adiabatic procedure. (a), (b) Electron energy distributions for electrons traveling to the right (blue curve) and to the left (red curve) calculated with TDSE for a pulse with the intensity $45 TW / {cm}^{2}$ and pulse duration 425.6 fs (a) and the intensity $50 TW / {cm}^{2}$ and pulse duration 266.0 fs (b). (c) Ionization rate calculated using Floquet theory vs time. (d), (e) The XFROG diagram of the radiation $E_{f} (t)$ calculated according Eq. (2) (color scale) and the corresponding polarization $P (t)$ (black line) according to the adiabatic theory (d) and for TDSE calculation (e). Vertical black lines indicate the “center” of the first resonance and the point in time symmetric in respect to the pulse center.
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Figure 4
XFROG diagram of a TDSE simulation for a two-bound-states-atom with the potential given by Eq. (4). Black lines are put at arbitrary points symmetric in respect to the center of the exciting pulse.
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Figure 5
Dependence of the atomic polarization $P$ on the carrier-envelope phase (CEP) in the adiabatic model (a) and for the direct solution of TDSE (b) for the CEP $θ = 0$ (blue lines) and $θ = π / 2$ (red lines).
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Figure 6
Dependence of the low frequency radiation component $\sim ω^{2} J (ω)^{2}$ on the pulse duration and intensity (note the logarithmic scale) according to the addiabatic model.
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