Classification of Nondipole Effects in Photoionization on the Attosecond Timescale

Advances in attosecond technology enable the measurement of nonlinear light–matter interaction at unprecedented timescales. However, attosecond-resolved nondipole processes in nonlinear photoionization, especially for partial wave resolved transition, still remain elusive, in the face of the challenges in identifying weak nondipole contributions from a background of dipole-allowed electronic dynamics. In this theoretical work, we employ circularly polarized extreme ultraviolet and infrared pulses to facilitate the unambiguous characterization of nondipole electronic dynamics, from 2-photon interferometric signals of angle-resolved photoelectron spectra. It is found that the ionized electronic waves via nondipole quantum transitions are notably delayed by around 10 as compared with dipole waves in their dispersion through atomic potential near 10 eV, which unravels how the centrifugal potential specifically affects both nondipole bound–continuum and continuum–continuum transitions.