Light-induced structures in attosecond transient-absorption spectroscopy of molecules

Jens E. Bækhøj and Lars Bojer Madsen

Phys. Rev. A 92, 023407 – Published 10 August 2015

Abstract

The nature of light-induced structures in attosecond transient-absorption spectroscopy of molecular systems is investigated theoretically. It is shown how nuclear dynamics affect these structures. We find that a theoretical three-surface model captures the main characteristics in the calculated spectra. Based on this model, nuclear dynamics is divided into different categories, each category having unique signatures in the absorption spectra. Finally, we discuss the possibility for experimental observation of light-induced structures in molecules.

Received 23 June 2015

DOI:https://doi.org/10.1103/PhysRevA.92.023407

Authors & Affiliations

Jens E. Bækhøj and Lars Bojer Madsen

Department of Physics and Astronomy, Aarhus University, 8000 Aarhus C, Denmark

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Vol. 92, Iss. 2 — August 2015

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Images

Figure 1
BO curves of our ${H_{2}}^{+}$ model. The thick, full line shows the ground state, while the narrower full lines are bright excited states and the dashed lines are excited dark states (see text). The vertical gray line indicates the value of $R_{0} = \int R {| G_{g} (R, t = - \infty) |}^{2} d R = 2.07$ .
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Figure 2
ATAS spectra $\tilde{S} (ω, τ)$ [Eq. (1)] of ${H_{2}}^{+}$ with fixed (left column) and moving (right column) nuclei. (a) Includes the six lowest electronic states in the calculation. The energy evaluated at $R_{0}$ of the four states in the energy range of interest are shown in the middle column. In the middle column full lines represent bright states and dashed lines represent dark states (see text). (b)–(e) Excludes the electronic states indicated by light-gray coloring in the middle column. Note that there are separate color bars for the left and right columns. The color bars are designed to highlight the LISs which are also encircled by black cigars in the fixed nuclei case. Pulse parameters: $T_{XUV} = 330$ as, $T_{NIR} = 14.0$ fs, $λ_{XUV} = 50$ nm, $λ_{NIR} = 700$ nm, $I_{XUV} = 5 \times 10^{7}$ W/ ${cm}^{2}, I_{NIR} = 2 \times 10^{12}$ W/ ${cm}^{2}$ .
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Figure 3
Illustration of possible arrangements of excited BO curves in molecules. Full lines represent bright states with respect to coupling from the ground-state curve, while dashed lines represent dark states.
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Figure 4
ATAS spectra of a model with two binding excited BO curves [see upper right part of Fig. 3]. The spectra are calculated for the different values of $R_{d}$ and $R_{e}$ [see Eq. (11)] $R_{d} = R_{e} = 0.0$ (a), $R_{d} = 0.0$ and $R_{e} = 0.3$ (b), $R_{d} = 0.3$ and $R_{e} = 0.0$ (c), $R_{d} = 0.3$ and $R_{e} = 0.3$ (d), $R_{d} = 0.5$ and $R_{e} = 0.0$ (e), and $R_{d} = 0.5$ and $R_{e} = 0.3$ (f). Special attention should be given to the spectral feature in (a) and (b) at $\sim 19$ eV. The insets show illustrations of the two excited BO curves included in the calculations. In the insets, the vertical gray line indicates $R = R_{0}$ . Pulse parameters are as in Fig. 2.
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Figure 5
ATAS spectra of a model with a single binding excited bright BO curve and a single dissociative dark BO curve [see lower left part of Fig. 3]. In the calculations $R_{e}$ of Eq. (11) is chosen as $R_{e} = 0$ (a) or $R_{e} = 0.3$ (b). The insets show illustrations of the two excited BO curves included in the calculations. In the insets, the vertical gray lines indicate $R = R_{0}$ . Pulse parameters are as in Fig. 2.
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Figure 6
ATAS spectra of a model with a single dissociative excited bright BO curve and a single binding dark BO curve [see lower right part of Fig. 3]. In the calculations $R_{d}$ of Eq. (11) is chosen as $R_{d} = 0$ (a) or $R_{d} = 0.3$ (b). The insets show illustrations of the two excited BO curves included in the calculations. In the insets, the vertical gray lines indicate $R = R_{0}$ . Pulse parameters are as in Fig. 2.
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