Double ionization of helium by a single intense (above ${10}^{18}\mathrm{W}/{\mathrm{cm}}^2$) linearly polarized extreme ultraviolet laser pulse is studied by numerically solving the full-dimensional time-dependent Schrödinger equation. For the laser intensities well beyond the perturbative limit, novel gridlike interference fringes are found in the correlated energy spectrum of the two photoelectrons. The interference can be traced to the multitude of two-electron wave packets emitted at different ionization times. A semianalytical model for the dressed two-photon double ionization is shown to qualitatively account for the interference patterns in the joint energy spectrum. Similar signatures of interferences between transient induced time-delayed ionization bursts are expected for other atomic and molecular multielectron systems.

• Received 19 March 2019

DOI:https://doi.org/10.1103/PhysRevLett.124.043203