In this paper we study the emergence of two-electron wave packets following the two-photon ionization of helium with intense near-femtosecond pulses. Monitoring the dynamics of the doubly ionized portion of the joint radial and energy distributions during the pulse's lifetime, we observe and examine the effects of strong Coulombic interactions which take place between electrons with partial waves other than the dominant $pp$ channels. The generated doubly ionized wave packets correspond to configurations where the two electrons remain close to the core and roughly equidistant until the pulse's peak; it is at later times that the sequential or nonsequential nature of the double-ionization process leads to distinctly different patterns. Moreover, we also show the difference in the evolution into the corresponding final-state distributions as the pulse's central photon energy varies between 42 and 70 eV and, thus, as the ionization mechanism transforms from the so-called nonsequential to the sequential ionization regime, respectively.

• Received 21 March 2023
• Revised 4 July 2023
• Accepted 7 September 2023

DOI:https://doi.org/10.1103/PhysRevA.108.043110