Exploring Laser-Induced Strong-Field Ionization Phenomena: Toward Dynamic 4D Imaging and Beyond

Accurate characterization of the intensity and duration of strong-field femtosecond pulses within the interaction volume is essential for attosecond science. However, achieving such precision remains a significant challenge, particularly in high harmonic generation experiments.

We introduce a novel in situ approach for spatially resolved measurement and control of strong-field femtosecond pulse intensity and duration within the focal region [1]. This method integrates conjugate focal imaging with in situ ion measurements under gas densities relevant to attosecond experiments. Additionally, we demonstrate dynamic four-dimensional (4D: 3D spatial + 1D temporal) laser-induced strong-field ionization tomography [2].

Independent measurements in helium and argon, coupled with fitting to a strong-field ionization dynamic model, yield accurate and consistent results over a wide range of gas densities. These results highlight the importance of double ionization and barrier suppression ionization mechanisms.

By enabling direct spatially resolved characterization of the driving laser, our approach addresses the averaging problem inherent to interaction volume measurements. This advancement enhances the accuracy and reliability of attosecond science experiments.

Our proof-of-principle dynamic tomographic imaging experiment uncovered an intriguing phenomenon: a "squeezing" effect in the gas pulse during downstream propagation. This effect manifests as a shortening of the normalized temporal profile of the gas pulse density along the propagation axis, accompanied by transverse expansion [2].

Our analysis identifies an operational regime characterized by significant resolution enhancement, unique intensity-resolution coupling, and localization phenomena driven by the underlying physics of strong-field interactions [3].

[1] N. Shlomo, E. Frumker, “In situ characterization of laser-induced strong field ionization phenomena”, Light: Science & Applications, 14 (166), 2025

[2] N. Shlomo, E. Frumker, “In Situ Dynamic Four-Dimensional Strong Field Ionization Tomography”, Physical Review Research, 7 (1), 2025

[3] E. Frumker, “Theory of Laser Induced Strong-Field Ionization Tomographic Imaging”, Opt. Express, 33 (5), 2025