Electron spectra from strong-field enhanced ionization in heavy water

Abstract

Strong-field enhanced ionization (EI) is a phenomenon in which stretching of interatomic bonds into a distorted molecular geometry leads to an increase in the tunneling ionization rate driven by a strong field. While the nuclear dynamics leading to EI are well established, the electron dynamics of the ionization step remain largely unexplored. Isolating the momentum distribution of the electrons involved in EI is critical to fully characterizing the phenomenon. We have measured the electron momentum distribution associated with EI in triple ionization of D₂O using 6-fs pulse pairs together with full fragment momentum imaging and electron-ion correlation methods. We find that the EI electron momentum distribution differs substantially from that of standard strong-field tunneling from molecules, exhibiting an increased yield of electrons with large momentum in the direction of the laser polarization, and a change from the expected Gaussian distribution. These observations indicate that the instantaneous EI tunneling rate is maximized at a critical value of the laser electric field, rather than at the peak of an optical cycle. This finding distinguishes EI from Keldysh tunneling rate predictions, where tunneling rate increases monotonically with field strength. These pronounced differences between EI and non-EI electron spectra are critical tests of models of enhanced ionization and suggest a route towards control of the sub-cycle timing of electron emission.

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Cite

BibTeX RIS

BibTeX

@misc{weckwerth2026electron,
  title = {{Electron spectra from strong-field enhanced ionization in heavy water}},
  author = {Eleanor Weckwerth and Chuan Cheng and Ian Gabalski and Andrew J. Howard and Mathew Britton and Aaron M. Ghrist and Haoran Ma and Salma A. Mohideen and Philip H. Bucksbaum},
  howpublished = {arXiv},
  year = {2026},
  month = sep,
  doi = {10.48550/arxiv.2605.27612},
  eprint = {2605.27612},
  archivePrefix = {arXiv},
  url = {https://arxiv.org/abs/2605.27612},
}

RIS

TY  - UNPB
TI  - Electron spectra from strong-field enhanced ionization in heavy water
AU  - Eleanor Weckwerth
AU  - Chuan Cheng
AU  - Ian Gabalski
AU  - Andrew J. Howard
AU  - Mathew Britton
AU  - Aaron M. Ghrist
AU  - Haoran Ma
AU  - Salma A. Mohideen
AU  - Philip H. Bucksbaum
PY  - 2026
DA  - 2026/09/15
PB  - arXiv
DO  - 10.48550/arxiv.2605.27612
UR  - https://arxiv.org/abs/2605.27612
AB  - Strong-field enhanced ionization (EI) is a phenomenon in which stretching of interatomic bonds into a distorted molecular geometry leads to an increase in the tunneling ionization rate driven by a strong field. While the nuclear dynamics leading to EI are well established, the electron dynamics of the ionization step remain largely unexplored. Isolating the momentum distribution of the electrons involved in EI is critical to fully characterizing the phenomenon. We have measured the electron momentum distribution associated with EI in triple ionization of D_2O using 6-fs pulse pairs together with full fragment momentum imaging and electron-ion correlation methods. We find that the EI electron momentum distribution differs substantially from that of standard strong-field tunneling from molecules, exhibiting an increased yield of electrons with large momentum in the direction of the laser polarization, and a change from the expected Gaussian distribution. These observations indicate that the instantaneous EI tunneling rate is maximized at a critical value of the laser electric field, rather than at the peak of an optical cycle. This finding distinguishes EI from Keldysh tunneling rate predictions, where tunneling rate increases monotonically with field strength. These pronounced differences between EI and non-EI electron spectra are critical tests of models of enhanced ionization and suggest a route towards control of the sub-cycle timing of electron emission.
ER  -

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