Ionization in elliptically polarized pulses: Multielectron polarization effects and asymmetry of photoelectron momentum distributions

N. I. Shvetsov-Shilovski, D. Dimitrovski, and L. B. Madsen

Phys. Rev. A 85, 023428 – Published 29 February 2012

Abstract

In the tunneling regime we present a semiclassical model of above-threshold ionization with inclusion of the Stark shift of the initial state, the Coulomb potential, and a polarization induced dipole potential. The model is used for the investigation of the photoelectron momentum distributions in close to circularly polarized light, and it is validated by comparison with ab initio results and experiments. The momentum distributions are shown to be highly sensitive to the tunneling exit point, the Coulomb force, and the dipole potential from the induced dipole in the atomic core. This multielectron potential affects both the exit point and the dynamics, as illustrated by calculations on Ar and Mg. Analytical estimates for the position of the maximum in the photoelectron distribution are presented, and the model is compared with other semiclassical approaches.

Received 27 January 2012

DOI:https://doi.org/10.1103/PhysRevA.85.023428

Authors & Affiliations

N. I. Shvetsov-Shilovski, D. Dimitrovski, and L. B. Madsen

Lundbeck Foundation Theoretical Center for Quantum System Research, Department of Physics and Astronomy, Aarhus University, 8000 Århus C, Denmark

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Vol. 85, Iss. 2 — February 2012

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Images

Figure 1
The 2D electron momentum distribution for ionization of Ar by a Ti:sapphire laser pulse ( $λ = 800$ nm) with a duration $n_{p} = 6$ cycles, peak intensity of $0.8 \times 10^{15}$ W/cm $^{2}$ , and ellipticity $ε = 0.78$ . The Keldysh parameter is $γ = 0.5$ . The offset angle $θ$ is shown on the figure. The black curve represents $- A (t)$ , where $A (t)$ is the vector potential corresponding to the field (23).Reuse & Permissions
Figure 2
The 2D electron momentum distributions in the polarization plane for ionization of H(1 $s$ ) by circularly polarized Ti:sapphire laser pulse with a duration $n_{p} = 3$ cycles and peak intensity of $10^{14}$ W/cm $^{2}$ . Panels (a) and (b) show results obtained by solving the TDSE, and using the classical simulations within the TIPIS model, respectively. The curves represent $- A (t)$ , where $A (t)$ is the vector potential, defined as in Ref. [75] for this particular figure.Reuse & Permissions
Figure 3
Momentum distributions of the photoelectrons emitted from Mg at a wavelength of 1600 nm and ellipticity $ε = 0.78$ calculated within the three different versions of semiclassical approaches. The left column, that is, panels (a), (d), and (g), shows the distributions, calculated ignoring the ionic potential after tunneling, when the tunneled electron moves in the laser field only. The middle column [panels (b), (e), and (h)] depicts the same distributions, but with consideration for the Coulomb field. The right column [panels (c), (f), and (i)] presents the results of the full TIPIS model, when both terms are taken into account in Eq. (4). The distributions (a)–(c), (d)–(f), and (g)–(i) correspond to the intensity of 2.35, 3.5, and $5.0 \times 10^{13}$ W/cm $^{2}$ , and to the Keldysh parameter of 1.05, 0.85, and 0.7, respectively. The same color scale is used for all the distributions.Reuse & Permissions
Figure 4
Momentum distributions of the photoelectrons emitted from Mg at a wavelength of 800 nm and ellipticity $ε = 0.78$ calculated within the three different versions of semiclassical approaches. The left column, that is, panels (a), (d), and (g), shows the distributions, calculated ignoring the ionic potential after tunneling, when the tunneled electron moves in the laser field only. The middle column [panels (b), (e), and (h)] depicts the same distributions, but with consideration for the Coulomb field. The right column [panels (c), (f), and (i)] presents the results of the full TIPIS model, when both terms are taken into account in Eq. (4). The distributions (a)–(c), (d)–(f), and (g)–(i) correspond to the intensity of 2.35, 3.5, and $5.0 \times 10^{13}$ W/cm $^{2}$ , and to the Keldysh parameter of 2.1, 1.7, and 1.4, respectively. The same color scale is used for all the distributions.Reuse & Permissions
Figure 5
The electron momentum distributions for ionization of Mg at a wavelength of 1600 nm for the ellipticity $ε = 0.78$ and two different intensities: (a), (b) $2.35 \times 10^{13}$ W/cm $^{2}$ and (c), (d) $3.5 \times 10^{13}$ W/cm $^{2}$ , which corresponds to the Keldysh parameter $γ$ of 1.05 and 0.85, respectively. The left column of the panels corresponds to the TIPIS model, whereas the right one presents the results of the FDM with the potential given by Eq. (4). In both cases Stark shifts and ME terms are included. The color scale is the same for all the panels.Reuse & Permissions

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