Spectra of the quardupole-dipole superlattice

The possible enhancement of quadrupole and magnetic transitions coming into resonance with dipole transitions in superlattices has been studied. The frequency dependences of the effective permittivity tensor of the superlattice are determined. The dispersion functions of hybrid dipole-quadrupole polariton branches are obtained. The effective strength of the quadrupole transition is determined as a function of the parameters of the dipole transition, which makes it possible to control the intensity and frequency of the quadrupole radiation. Polaritons can have a negative group velocity if they propagate in a direction other than the optic axis of the superlattice.