Two-electron processes in multiple ionization under strong soft-x-ray radiation

In a combined experimental and theoretical study we have investigated the ionization of atomic argon upon irradiation with intense soft-x-ray pulses of 105 eV photon energy from the free-electron laser FLASH. The measured ion yields show charge states up to Ar7+. The comparison with the theoretical study of the underlying photoionization dynamics highlights the importance of excited states in general and of processes governed by electron correlation in particular, namely, ionization with excitation and shake-off, processes usually inaccessible by measurements of ionic yields only. The Ar7+ yield shows a clear deviation from the predictions of the commonly used model of sequential ionization via single-electron processes and the observed signal can only be explained by taking into account the full multiplet structure of the involved configurations and by inclusion of two-electron processes. The competing process of two-photon ionization from the ground state of Ar6+ is calculated to be orders of magnitude smaller

Atomic-resolution imaging of carbonyl sulfide by laser-induced electron diffraction

Measurements on the strong-field ionization of carbonyl sulfide molecules by short, intense, 2 µm wavelength laser pulses are presented from experiments where angle-resolved photoelectron distributions were recorded with a high-energy velocity map imaging spectrometer, designed to reach a maximum kinetic energy of 500 eV. The laser-field-free elastic-scattering cross section of carbonyl sulfide was extracted from the measurements and is found in good agreement with previous experiments, performed using conventional electron diffraction. By comparing our measurements to the results of calculations, based on the quantitative rescattering theory, the bond lengths and molecular geometry were extracted from the experimental differential cross sections to a precision better than ±5 pm and in agreement with the known values

Stability and Tunneling Dynamics of a Dark-Bright Soliton Pair in a Harmonic Trap

http://journals.aps.org/pra/abstract/10.1103/PhysRevA.91.04363

Creation of double ion hole states 3s⁰3p^<em>n</em> with 2 ≤ <em>n</em> ≤ 6, in dependence on the intensity

<p><strong>Figure 5.</strong> Creation of double ion hole states 3s⁰3p^<em>n</em> with 2 ≤ <em>n</em> ≤ 6, in dependence on the intensity.</p> <p><strong>Abstract</strong></p> <p>We present calculations on the multiple ionization of argon at the photon energy 123 eV and pulse duration 50 fs. At that photon energy, it is possible to drive the two-photon resonant Auger transition 2p → 4p, whose lifetime is 5.5 fs, much shorter than the pulse duration. The excitation of a 2p electron to the 4p state thus creates a hole which decays by an Auger process. We have also included above-threshold ionization from the outer shells of the neutral and singly ionized species, which becomes significant at intensities of the order of ~10¹⁵ W cm⁻² and higher. The populations of the various ionic species were obtained through the solution of the kinetic equations governing their production and decay during the pulse. The effect of the intensity distribution in the interaction volume has also been evaluated. We have further shown that doubly hollow ionic states of the type 3s⁰3p^<em>n</em> with 2 ≤ <em>n</em> ≤ 6 are created, which can decay only via spontaneous emission, with lifetimes orders of magnitude longer than the pulse duration. These hollow-ion states can potentially serve as a starting point for a variety of experimental investigations on doubly excited states.</p

Overall yields of argon ions up to Ar^{7 +} under a Gaussian pulse of 50 fs duration and 123 eV photon energy

<p><strong>Figure 2.</strong> Overall yields of argon ions up to Ar^{7 +} under a Gaussian pulse of 50 fs duration and 123 eV photon energy. ATI leading to singly and doubly ionized argon has been included separately (dashed lines), as well as the Ar⁺ ions due to the Auger effect (dash–dotted line, green).</p> <p><strong>Abstract</strong></p> <p>We present calculations on the multiple ionization of argon at the photon energy 123 eV and pulse duration 50 fs. At that photon energy, it is possible to drive the two-photon resonant Auger transition 2p → 4p, whose lifetime is 5.5 fs, much shorter than the pulse duration. The excitation of a 2p electron to the 4p state thus creates a hole which decays by an Auger process. We have also included above-threshold ionization from the outer shells of the neutral and singly ionized species, which becomes significant at intensities of the order of ~10¹⁵ W cm⁻² and higher. The populations of the various ionic species were obtained through the solution of the kinetic equations governing their production and decay during the pulse. The effect of the intensity distribution in the interaction volume has also been evaluated. We have further shown that doubly hollow ionic states of the type 3s⁰3p^<em>n</em> with 2 ≤ <em>n</em> ≤ 6 are created, which can decay only via spontaneous emission, with lifetimes orders of magnitude longer than the pulse duration. These hollow-ion states can potentially serve as a starting point for a variety of experimental investigations on doubly excited states.</p

Outline of the paths of ionization

<p><strong>Figure 1.</strong> Outline of the paths of ionization. Note that for each transition channel, there are manifolds of fine structure states which have been accounted for in the calculation but are too many to be included in the figure.</p> <p><strong>Abstract</strong></p> <p>We present calculations on the multiple ionization of argon at the photon energy 123 eV and pulse duration 50 fs. At that photon energy, it is possible to drive the two-photon resonant Auger transition 2p → 4p, whose lifetime is 5.5 fs, much shorter than the pulse duration. The excitation of a 2p electron to the 4p state thus creates a hole which decays by an Auger process. We have also included above-threshold ionization from the outer shells of the neutral and singly ionized species, which becomes significant at intensities of the order of ~10¹⁵ W cm⁻² and higher. The populations of the various ionic species were obtained through the solution of the kinetic equations governing their production and decay during the pulse. The effect of the intensity distribution in the interaction volume has also been evaluated. We have further shown that doubly hollow ionic states of the type 3s⁰3p^<em>n</em> with 2 ≤ <em>n</em> ≤ 6 are created, which can decay only via spontaneous emission, with lifetimes orders of magnitude longer than the pulse duration. These hollow-ion states can potentially serve as a starting point for a variety of experimental investigations on doubly excited states.</p

Relaxation of the excited states of argon ions via spontaneous emission: (a) Ar⁺, (b) Ar^{2 +}, (c) Ar^{3 +}, (d) Ar^{4 +}, (e) Ar^{5 +} and (f) Ar^{6 +}

<p><strong>Figure 4.</strong> Relaxation of the excited states of argon ions via spontaneous emission: (a) Ar⁺, (b) Ar^{2 +}, (c) Ar^{3 +}, (d) Ar^{4 +}, (e) Ar^{5 +} and (f) Ar^{6 +}.</p> <p><strong>Abstract</strong></p> <p>We present calculations on the multiple ionization of argon at the photon energy 123 eV and pulse duration 50 fs. At that photon energy, it is possible to drive the two-photon resonant Auger transition 2p → 4p, whose lifetime is 5.5 fs, much shorter than the pulse duration. The excitation of a 2p electron to the 4p state thus creates a hole which decays by an Auger process. We have also included above-threshold ionization from the outer shells of the neutral and singly ionized species, which becomes significant at intensities of the order of ~10¹⁵ W cm⁻² and higher. The populations of the various ionic species were obtained through the solution of the kinetic equations governing their production and decay during the pulse. The effect of the intensity distribution in the interaction volume has also been evaluated. We have further shown that doubly hollow ionic states of the type 3s⁰3p^<em>n</em> with 2 ≤ <em>n</em> ≤ 6 are created, which can decay only via spontaneous emission, with lifetimes orders of magnitude longer than the pulse duration. These hollow-ion states can potentially serve as a starting point for a variety of experimental investigations on doubly excited states.</p

Argon ionization products after volume integration

<p><strong>Figure 3.</strong> Argon ionization products after volume integration.</p> <p><strong>Abstract</strong></p> <p>We present calculations on the multiple ionization of argon at the photon energy 123 eV and pulse duration 50 fs. At that photon energy, it is possible to drive the two-photon resonant Auger transition 2p → 4p, whose lifetime is 5.5 fs, much shorter than the pulse duration. The excitation of a 2p electron to the 4p state thus creates a hole which decays by an Auger process. We have also included above-threshold ionization from the outer shells of the neutral and singly ionized species, which becomes significant at intensities of the order of ~10¹⁵ W cm⁻² and higher. The populations of the various ionic species were obtained through the solution of the kinetic equations governing their production and decay during the pulse. The effect of the intensity distribution in the interaction volume has also been evaluated. We have further shown that doubly hollow ionic states of the type 3s⁰3p^<em>n</em> with 2 ≤ <em>n</em> ≤ 6 are created, which can decay only via spontaneous emission, with lifetimes orders of magnitude longer than the pulse duration. These hollow-ion states can potentially serve as a starting point for a variety of experimental investigations on doubly excited states.</p