Excitation of E1-forbidden Atomic Transitions with Electric, Magnetic or Mixed Multipolarity in Light Fields Carrying Orbital and Spin Angular Momentum

Photons carrying a well-defined orbital angular momentum have been proven to modify spectroscopic selection rules in atomic matter. Excitation profiles of electric quadrupole transitions have been measured with single trapped ${}^{40}$Ca${}^{+}$ ions for varying polarizations. We further develop the photo-absorption formalism to study the case of arbitrary alignment of the beam’s optical axis with respect to the ion’s quantization axis and mixed multipolarity. Thus, predictions for M1-dominated ${}^{40}A{r}^{13+}$, E3-driven ${}^{171}Y{b}^{+}$ and ${}^{172}Y{b}^{+}$, and B-like ${}^{20}N{e}^{5+}$ are presented. The latter case displays novel effects, coming from the presence of a strong photon – magnetic dipole coupling.