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arXiv · 2604.03943

Photoelectron spectroscopy of 3s3p doubly excited helium dressed with strong near-infrared laser fields

Mizuho Fushitani·Chien-Nan Liu·Yuki Ono·Shunsuke Amaike·Wataru Yamazaki·Keiko Kato·Akitaka Matsuda·Shigeki Owada·Makina Yabashi·Yasumasa Hikosaka·Toru Morishita·Akiyoshi Hishikawa
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Abstract

We report time-resolved photoelectron spectroscopy of the $3s3p$ doubly excited states of helium dressed by an intense near-infrared (NIR) laser field. Using synchronized XUV free-electron-laser and 800-nm NIR laser pulses, we observe a pronounced delay-dependent shift of resonance-related spectral minima together with the emergence of additional structures around the NIR sideband energy. \textit{Ab initio} theoretical calculations support these observations and identify the features as signatures of NIR-induced coupling of the bright ($3s3p {}^{1}P^{o}$) autoionizing state to nearby dark ($^{1}D^{e}$ and $^{1}S^{e}$) resonances below the $N = 3$ threshold. A multichannel Fano resonance analysis of the measured spectra yields delay-dependent line-shape parameters and resonance energies, establishing a quantitative route to characterize and control correlated two-electron resonances in strong laser fields.

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Mizuho Fushitani, Chien-Nan Liu, Yuki Ono, Shunsuke Amaike, Wataru Yamazaki, Keiko Kato, Akitaka Matsuda, Shigeki Owada, Makina Yabashi, Yasumasa Hikosaka, Toru Morishita, Akiyoshi Hishikawa. 2026-04-05. Photoelectron spectroscopy of 3s3p doubly excited helium dressed with strong near-infrared laser fields. https://doi.org/10.1103/d8qn-8y4v

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