... (i.e., also S ∼ k),i.e., one is dealing with totally usual relations as in a vacuum (the so-calledordinary beam). In contrast, for orthogonal polarization the vectors E and D(and S and k) have ... that one speaks of an extraordinarybeam.If the phase-propagation vector k is, e.g., in the (x1,x3)-plane under a gen-eral angle, then the in-plane polarized wave is ordinary,whereasthewavepolarized ... the incident wave has contributions from both polarizations. As a consequence, even if in vacuo the wave has a unique linear polarization di-rection (not parallel to a principal axis of the dielectric...