Electric Nondipole Effect in Strong-Field Ionization

Strong-field ionization of atoms by circularly polarized femtosecond laser pulses produces a donut-shaped electron momentum distribution. Within the dipole approximation this distribution is symmetric with respect to polarization plane. The magnetic component light field known shift forward. Here, we show that non-dipole effect not only in strong-field ionization. We find an electric arises due position dependence and which can be understood analogy Doppler effect. This manifests as increase radius photoelectron for forward-directed momenta decrease backwards-directed electrons. present experimental data showing fingerprint compare our findings classical model quantum calculations.