Polarization correlations in the two--photon decay of hydrogen--like ions

TL;DR

This paper investigates the polarization correlations of photons emitted during the two-photon decay of hydrogen-like ions, analyzing relativistic and non-dipole effects through detailed theoretical calculations.

Contribution

It derives a polarization correlation function for two-photon decay and applies it to various ions, highlighting relativistic and non-dipole influences on polarization.

Findings

Polarization correlations vary with ion type and transition.

Relativistic effects significantly influence polarization properties.

Non-dipole contributions are non-negligible in heavy ions.

Abstract

Polarization properties of the photons emitted in the two-photon decay of hydrogen-like ions are studied within the framework of the density matrix and second-order perturbation theory. In particular, we derive the polarization correlation function that gives the probability of the (two-photon) coincidence measurement performed by polarization-sensitive detectors. Detailed calculations of this function are performed for the $2s_{1/2} \to 1s_{1/2}$ transition in neutral hydrogen as well as Xe$^{53+}$ and U$^{91+}$ ions. The obtained results allow us to understand the influence of relativistic and non-dipole effects on the polarization correlations in the bound-bound two-photon transitions in heavy ions.