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

Abstract

Owing to vortex light possessing the additional orbital angular momentum, its interaction with atoms and molecules can reveal in more depth insights into dynamics than the plane wave light. This paper aims to establish a theoretical framework for the photoionization of atoms and molecules by vortex light. In the case of macroscopic gas target, helium atoms are randomly dispersed around the entire region of the Bessel vortex beam. The final photoionization cross-section is not dependent on the angular momentum of the vortex light; on the contrary, it depends on the opening angle of the Bessel vortex light. This paper systematically compute the variation of photoionization cross-section with photon energy and the angular distributions of photoelectrons under different geometric conditions. The computation results demonstrate that there is a significant difference in the photo-ionization cross-section between vortex light and plane wave light. In order to further investigate the characteristics of the phase singularity of the vortex light (when the light intensity reaches zero), this paper further calculates the photo-ionization of the vortex light with opening angles of 5°, 30°, and 60° at the phase singularity, respectively. The research results indicate that the angular distribution of photoelectrons at these three angles is significantly dependent on 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 interacting with atoms, distinguishing it from the plane wave. This work lays the foundation for further studying vortex light photo-ionization and their applications.