Linearly polarized RABBIT beyond the dipole approximation

We theoretically investigate nondipole effects in the reconstruction of attosecond beating by interference of two-photon transitions (RABBIT) of helium using linearly polarized extreme ultraviolet and infrared fields. By scanning the time delay between the two fields, we observe modulations in sidebands (SBs) both for angular-integrated photoelectron yield and forward-backward asymmetry in photoelectron distribution along the light-propagation direction. The SB modulations of the forward-backward asymmetry reveal Wigner and continuum-continuum time delays of the electron wave packets ionized via nondipole paths, different from the conventional RABBIT where only the dipole paths are involved. Furthermore, the time delays extracted from the forward-backward asymmetry show an abrupt jump as a function of polar emission angle of photoelectrons, due to the competition among continuum partial waves in nondipole laser-assisted photoionization.