Interaction of twisted light with many-electron atoms and ions

Abstract

The excitation of many-electron atoms and ions by twisted light has been studied within the framework of the density-matrix theory and Dirac's relativistic equation. Special attention is paid to the magnetic sublevel population of excited atomic states as described by means of the alignment parameters. General expressions for the alignment of the excited states are obtained under the assumption that the photon beam, prepared as a coherent superposition of two twisted Bessel states, irradiates a macroscopic target. We demonstrate that for this case the population of excited atoms can be sensitive to both the transverse momentum and the (projection of the) total angular momentum of the incident radiation. While the expressions are general and can be employed to describe the photoexcitation of any atom, independent on its shell structure and number of electrons, we performed calculations for the $3s\ensuremath{\rightarrow}3p$ transition in sodium. These calculations indicate that the ``twistedness'' of incoming radiation can lead to a measurable change in the alignment of the excited $^{2}P_{3/2}$ state as well as the angular distribution of the subsequent fluorescence emission.