Review on non-dipole effects in ionization and harmonic generation of atoms and molecules

In this review,we will focus on recent progress on the investigations of nondipole effects in few-electron atoms and molecules interacting with light fields.We first briefly survey several popular theoretical methods and relevant concepts in strong field and attosecond physics beyond the dipole approximation.Physical phenomena stemming from the breakdown of the dipole approximation are then discussed in various topics,including the radiation pressure and photon-momentum transfer,the atomic stabilization,the dynamic interference,and the high-order harmonic generation.Whenever available,the corresponding experimental observations of these nondipole effects are also introduced respectively in each topics.

Laser-Induced Electron Fresnel Diffraction in Tunneling and Over-Barrier Ionization

Photoelectron momentum distribution in strong-field ionization has a variety of structures that reveal the complicated dynamics of this process.Recently,we identified a low-energy interference structure in the case of a super-intense extreme ultraviolet(XUV)laser pulse and attributed it to the laser-induced electron Fresnel diffraction.This structure is determined by the laser-induced electron displacement[Geng et al.Phys.Rev.A104(2021)L021102].In the present work,we find that the Fresnel diffraction picture also appears in the tunneling and over-barrier regime of ionization by short pulses.However,the electron displacement is now induced by the electric field component of the laser pulse rather than the magnetic field component in the case of the super-intense XUV pulse.After corresponding modifications to our quantum and semiclassical models,we find that the same physical mechanism of the Fresnel diffraction governs the low-energy interference structures along the laser polarization.The results predicted by the two models agree well with the accurate results from the numerical solution to the time-dependent Schr¨odinger equation.