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arXiv:2505.21788 · Physical Review A

Optical interference effect in strong-field electronic coherence spectroscopy

Eleanor Weckwerth, Andrew J. Howard, Chuan Cheng, Ian Gabalski, Aaron M. Ghrist, Salma A. Mohideen, C. D. Lin, Chi Hong Yuen, P. H. Bucksbaum

Published Sep 12, 2025• 1 citation
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Abstract

The authors present a combined experimental and theoretical study of strong-field-induced electronic coherences in argon and molecular nitrogen ions as a step towards strong-field coherent control in molecular chemistry. They find that nonsequential double ionization in the low-intensity region of the focal volume can reduce the visibility of coherence generated by two-pulse sequential ionization, and quantify the importance of pulse shape and spectral characteristics for isolating the desired coherence signals.

DOI
10.1103/rkdq-5skq

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The authors present a combined experimental and theoretical study of strong-field-induced electronic coherences in argon and molecular nitrogen ions as a step towards strong-field coherent control in molecular chemistry. They find that nonsequential double ionization in the low-intensity region of the focal volume can reduce the visibility of coherence generated by two-pulse sequential ionization, and quantify the importance of pulse shape and spectral characteristics for isolating the desired coherence signals.
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The strong-field coherent control of the nonresonant ionization of nitrous oxide using shaped pulses is investigated. We study the dependence of periodic coherent oscillation of the total ionization yield on the variation of laser phase parameters. The physical mechanism of the strong-field coherent control is investigated experimentally and theoretically by the nonresonant spectral phase interferences in the frequency domain. We show that the intense shaped pulses with broadband and off-resonance can be used as a robust strong-field coherent control method.
Atomic and molecular ions generated by a strong optical laser pulse are not in general in the electronic ground state. The density matrix for such ions is characterized by the electronic quantum-state populations and by the coherences among the electronic quantum states. Nonvanishing coherences signal the presence of coherent electronic wave-packet dynamics in the laser-generated ions. For noble-gas atoms heavier than helium, the most important channels populated via strong-field ionization are the outer-valence single-hole states with a total angular momentum of j=3/2j=3/2j=3/2 or j=1/2j=1/2j=1/2. For this case, we develop a time-dependent multichannel theory of strong-field ionization. We derive the ion density matrix and express the hole density in terms of the elements of the ion density matrix. Our wave-packet calculations demonstrate that neon ions generated in a strong optical field (800 nm) are almost perfectly coherent. In strong-field-generated xenon ions, however, the coherence is substantially suppressed.
We report a combined theoretical and experimental investigation on the unambiguous role of electronic coherence underlying the generation of laserlike coherent emission from N2+{{\mathrm{N}}_{2}}^{+}N2​+ ions launched in a strong laser field. The coherence manifests itself by giving rise to a dramatic enhancement of N2+{{\mathrm{N}}_{2}}^{+}N2​+ laserlike radiation with two temporally separated pump laser pulses centered at 800- and 1580-nm wavelengths, respectively. We further show that coherent control of N2+{{\mathrm{N}}_{2}}^{+}N2​+ lasing in a subfemtosecond timescale can be achieved by replacing the single 800-nm laser pulse with a pair of 800-nm laser pulses of adjustable time delay. The experimental results are well reproduced in theory using a three-level quantum model of N2+{{\mathrm{N}}_{2}}^{+}N2​+ ions under the density matrix representation.
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