Theoretical study on the photo-ionization of helium atoms by Bessel vortex light

Abstract

Due to the additional orbital angular momentum possessed by vortex light, its interaction with atoms and molecules can unveil deeper dynamical insights compared to those obtained with plane wave light. This paper aims to establish a theoretical framework for the photoionization of atoms and molecules by vortex light. In the context of macroscopic gas targets, helium atoms are randomly dispersed in the vicinity of the entire expanse of the Bessel vortex beam. The ultimate photoionization cross-section is not contingent upon the angular momentum of the vortex light; instead, it hinges on the opening angle of the Bessel vortex light. This paper undertakes a systematic computation of the variation pattern of the photoionization cross-section with respect to photon energy, as well as the angular distribution of photoelectrons under diverse geometric conditions. The computed results demonstrate that the photoionization cross-section of the vortex light differs markedly from that of the plane wave light. To delve deeper into the characteristics of the phase singularity (where the light intensity reaches zero) of the vortex light, this paper further calculates the photoionization at the phase singularity of the vortex light with opening angles of 5°, 30°, and 60° respectively. The research findings reveal that the angular distribution of photoelectrons at this juncture is significantly reliant on both the orbital angular momentum and the opening angle of the vortex light, and the calculated absolute cross-section does not equate to zero. This represents an important distinguishing feature of the Bessel vortex light when it interacts with atoms, setting it apart from the plane wave. This work lays the groundwork for further studies on vortex light photoionization and their applications.