Quantum theory of the Hanle effect - Calculations of the Stokes parameters of the D3 helium line for quiescent prominences
Résumé
A formalism of the quantum theory of the Hanle effect is developed to obtain the Stokes parameters of the D3 line in quiescent prominences in the presence of a stationary magnetic field. The aim is to develop a method that can be used to determine the vector magnetic field in prominences. The quantum description of an ensemble of atoms or photons in terms of a density matrix is briefly recalled, and the evolution of the time-dependent density matrix of the atom is treated by means of a master equation in which the interaction between the scattering atom, the incident photons, and the magnetic field appears. The approximations leading to the master equation are discussed. The expression for the density matrix of the reemitted photons is given as a function of the atomic density matrix calculated for the steady state. The formalism has been used for explicit calculations of the D3 polarization in an earlier paper by Sahal-Brechot et al. (1977).