Complete suppression of the non-dipole drift effect in high harmonic generation

Abstract

In high harmonic generation (HHG), non-dipole effects become increasingly significant at long driving wavelengths, as the magnetic field leads to a lateral drift of the continuum electron, which disrupts the electron recollision and inhibits the harmonic emission. To address this problem, we revisit the dynamics of the continuum electrons under electromagnetic fields in the HHG process and show that the magnetic effect on the drift includes a fundamental-frequency and a double-frequency component. By adding an additional field to counteract the double-frequency effect caused by the magnetic field, we construct an effective linearly polarized field that recovers the recollision of all returning electrons to the parent ion. Consequently, the harmonic yield is restored and becomes the same as the result within the dipole approximation across the broad spectral range. This work provides a scheme that completely suppresses the non-dipole drift effect and fully compensates for the harmonic yield reduction, paving the way to efficiently generate coherent radiation in the range from extreme ultraviolet to soft x-ray and ultrashort pulses based on HHG.