Maximum Elliptical Dichroism in Atomic Two-Photon Ionization

TL;DR

This paper theoretically demonstrates that maximum elliptical dichroism of magnitude 1 occurs in atomic two-photon ionization when the photon energy is tuned to resonances, with potential applications in analyzing laser polarization.

Contribution

It reveals the conditions for maximum elliptical dichroism in atomic two-photon ionization and proposes helium as a test case for experimental verification.

Findings

Maximum dichroism |Δ_ED|=1 in two-photon ionization.

Maximum dichroism occurs when electron emission is resonance-dominated.

Potential use in polarization analysis of free-electron laser beams.

Abstract

Elliptical dichroism is known in atomic photoionization as the difference in the photoelectron angular distributions produced in nonlinear ionization of atoms by left- and right-handed elliptically polarized light. We theoretically demonstrate that the maximum dichroism |{\Delta}_{ED}|=1 always appears in two-photon ionization of any atom if the photon energy is tuned in so that the electron emission is dominantly determined by two intermediate resonances. We propose the two-photon ionization of atomic helium in order to demonstrate this remarkable phenomenon. The maximum elliptical dichroism could be used as a sensitive tool for analyzing the polarization state of photon beams produced by free-electron lasers.