Strong-field ionization of excited Lithium atoms with optical vortex beams

Optical vortex beams, characterized by the phase variation of their wavefront, carry orbital angular momentum (OAM), which can influence atomic and molecular systems by altering the conventional selection rules for electronic transitions. The manifestation of OAM transfer can in principle be observed in the resulting structure of the photoelectron momentum distribution. However, in gas-phase atoms, efficient OAM transfer occurs primarily near the beam's center, precisely where the field intensity is minimal. This inherent challenge complicates experimental observations, as efficient OAM transfer necessitates effective sampling of the field's phase variation by the electronic wavefunction of the atom. In this study, we investigate multi-photon ionization of Lithium atoms under the influence of an intense optical vortex beam, employing a numerical treatment to solve the time-dependent Schrödinger equation in an inhomogeneous field. We explore the ionization rate and OAM transfer dynamics for Lithium atoms in various excited states and positioned at different distances from the beam center. Our analysis reveals the conditions required for successful experimental implementation and sheds light on novel strong-field phenomena associated with electron dynamics in a vortex beam.