High-order harmonic generation with orbital angular momentum beams: Beyond-dipole corrections

We study high harmonic generation with vortex beams beyond the dipole approximation. To do so, we employ the full minimal coupling approach to account for multipolar coupling without truncation and describe the full spatio-temporal properties of the electromagnetic field. This allows us to investigate the beyond-dipole deviations in electron trajectories and the harmonic spectra, where the influence of the orbital angular momentum contains both magnetic and quadrupolar effects. We show that when the system is driven by plane-wave light, nonlinear dipole oscillations occur along both the polarization and propagation directions, consistent with previous findings. In contrast, vortex beams also generate nonlinear dipole oscillations in the direction perpendicular to both the polarization and propagation of the incoming field. We identify the effects of the resulting symmetry breaking due to beyond-dipole corrections, which are especially visible in even harmonics.