Strong-field Ionization and Harmonic Generation with Optical Vortex Beams*

Vortex beams carry two types of angular momentum: spin angular momentum (SAM) due to the time-dependence of the light polarization, and orbital angular momentum (OAM) due to the spatial phase variation of their wavefront. In this work, we will first consider the transfer of OAM in the photoionization of excited Lithium atoms near the singularity of an optical vortex beam. In addition, we will explore the process of high-order harmonic generation (HHG) of an atomic gas exposed to a vortex beam, considering the collective response of the atoms. We show that the harmonics produced by an intense few-cycle optical vortex beam exhibit a mixture of OAMs, indicating the emergence of high-order processes and the breakdown of the perturbative regime as we increase the pulse intensity. The produced far field exhibits a complex light intensity profile and phase variation.