Theoretical calculation of the foil tilt angle dependence of the stokes parameters

The foil tilt angle dependence of the Stokes parameters has been calculated assuming the existence of a strong electric field perpendicular to the foil surface. The second order results obtained by Y.B. Band (Phys. Rev. 13 (1976) 2061) have been generalized by taking into account the energy separations between the levels. This has lead to a supplementary tilt angle dependent term which is linear in the electric field and the energy differences. The most important consequence of this term is that the Stokes parameters C and S are no longer proportional which is in agreement with the experimental results for the 4d 1D level in He I (R.M. Schectman et al., Phys. Rev. 22 (1980) 1591). The results of this second order perturbation calculation have been compared with the Stokes parameters evaluated exactly. This was done by resolving numerically the set of differential equations for the density matrix taking into account the coupling between four levels (s, p, d, f).