Attosecond Coherent Control of Single and Double Photoionization in Argon

C. W. Hogle, X. M. Tong, L. Martin, M. M. Murnane, H. C. Kapteyn, and P. Ranitovic

Phys. Rev. Lett. 115, 173004 – Published 22 October 2015

Abstract

Ultrafast high harmonic beams provide new opportunities for coherently controlling excitation and ionization processes in atoms, molecules, and materials on attosecond time scales by employing multiphoton two-pathway electron-wave-packet quantum interferences. Here we use spectrally tailored and frequency tuned vacuum and extreme ultraviolet harmonic combs, together with two phase-locked infrared laser fields, to show how the total single and double photoionization yields of argon can be coherently modulated by controlling the relative phases of both optical and electronic-wave-packet quantum interferences. This Letter is the first to apply quantum control techniques to double photoionization, which is a fundamental process where a single, high-energy photon ionizes two electrons simultaneously from an atom.

Received 14 December 2014

DOI:https://doi.org/10.1103/PhysRevLett.115.173004

Authors & Affiliations

C. W. Hogle¹, X. M. Tong², L. Martin¹, M. M. Murnane¹, H. C. Kapteyn¹, and P. Ranitovic^1,3,4,*

¹JILA and Department of Physics, University of Colorado and NIST, Boulder, Colorado 80309, USA
²Division of Materials Science, Faculty of Pure and Applied Science, University of Tsukuba, Ibaraki 305-8573, Japan
³Lawrence Berkeley National Lab,1 Cyclotron Road, Berkeley, California 94720, USA
⁴ELI-ALPS, ELI-Hu Nkft, Dugonics ter 13, Szeged H6720, Hungary

^*Corresponding author. pranitovic@lbl.gov

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Vol. 115, Iss. 17 — 23 October 2015

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Images

Figure 1
Experimental setup (bottom) and energy level diagram (top) showing both the relative amplitudes of the harmonics used in the calculation, as well as the relevant energy levels near the single- and double-ionization threshold of Ar. Multilayer mirrors spectrally select VUV ( $7 ω$ , $9 ω$ , and $11 ω$ ) and XUV ( $25 ω$ and $27 ω$ ) harmonics. Changes in gas pressure, due to the increase of the plasma term in the waveguide, can continuously blueshift the central energy of the harmonic comb, making it more or less resonant with the ${Ar}^{*}$ Rydberg states, as indicated in red and blue, respectively. Pressure tuning can also select whether one ( $25 ω$ ) or two ( $25 ω$ and $27 ω$ ) harmonics excite or ionize ${Ar}^{+} / {Ar}^{+ +}$ around the double-ionization threshold. Inset (a) shows the calculated ${Ar}^{+}$ yield for resonant and nonresonant excitation using a VUV pump and IR probe. Inset (b) shows a change in the periodicity of the ${Ar}^{+}$ yield when an additional weak IR pump pulse is added and locked in phase with the VUV pump pulse. The reflectance of the multilayer mirrors is shown in dashed gray.
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Figure 2
Experimental and theoretical ${Ar}^{+}$ yields as the time delay between the VUV/IR pump and the IR probe is varied. The insets enlarge the region near time zero, on attosecond time scales. (a) ${Ar}^{+}$ yield when the seventh and ninth harmonics are mostly not resonant with ${Ar}^{*}$ states; (b) shows the corresponding theoretical calculation. (c) ${Ar}^{+}$ yield when the seventh and ninth harmonics are resonant with ${Ar}^{*}$ ; (d) shows the corresponding simulation. Both (a) and (b) show an ${Ar}^{+}$ yield enhancement only when the pump and probe pulses are overlapped, and exhibit half-cycle oscillations. In contrast, (c) and (d) show a steplike enhancement of the ${Ar}^{+}$ yield, as well as full-cycle oscillations of the yield.
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Figure 3
Photoelectron energies taken in coincidence with the ${Ar}^{+}$ yield for nonresonant excitation are shown in (a) experiment and (b) simulation. Both exhibit half-cycle oscillations. (c),(d) Experimental and theoretical photoelectron energies for the case of resonant excitation, with the HHG blue shifted to higher energy, where both exhibit full-cycle oscillations. For both nonresonant and resonant excitation, the $10 ω$ band appears only when the probe IR field is present and coincides with the ${Ar}^{+}$ yield enhancement shown in Fig. 2.
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Figure 4
${Ar}^{+ +}$ yield modulation under nonresonant excitation: (a) experiment and (b) theory. (c),(d) ${Ar}^{+ +}$ yields in the case of resonant excitation, when the VUV harmonics are resonant with ${Ar}^{*}$ Rydberg states. For nonresonant excitation, both $25 ω$ and $27 ω$ are reflected from the XUV mirror, while in the blueshifted (resonant) case, only $25 ω$ is strongly reflected, as shown in Fig. 1. The dashed line in (d) includes a small amplitude $23 ω$ that modulates ${Ar}^{+ +}$ due to two-pathway quantum interferences via resonant excitation.
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