Sub-cycle resolution of field-momentum transfer in non-dipole strong-field ionization

Non-dipole effects in strong-field ionization are observed at high laser intensities and/or long wavelengths that both lead to high kinetic energies of the photoelectrons [1]. At longer wavelengths, the electron is influenced by the magnetic field component of the laser field even at moderate intensity [2]. In cases where the Coulomb field can be neglected, the magnetic field component is responsible for a momentum shift in beam propagation direction (p z ) of the final photoelectron momentum distribution (PMD) [3]. Here, we present for the first time a sub-cycle-resolved measurement of this momentum shift.