Eigenvalue problem for q-medium

The role of the quadrupole moment for the interaction of electromagnetic waves with matter is discussed. Using an artificial chiral medium as an example, it is shown that optical activity is not affected by the quadrupole polarization induced by the tensor Q_αβ=q_αγβ⁽⁰⁾ E_β. Also it is demonstrated by the example of the simplest composite material (a dielectric matrix loaded with dielectric spheres) that the quadrupole response may be represented as Q_αγ=q_αγβδ ⁽¹⁾∇_δE_β. The latter form leads to the change of birefringence parameters only