Dispersion relations for the refractive indices of normal waves

The analytical properties of the refractive indices of normal waves are considered, for the example of normal waves in laminar media and surface waves. It is shown that the possibility of wave transmission through the layer is characterized by the appearance of branching points in functions of the refractive index not lying on the real frequency axis and violating the condition of applicability of dispersion relations of Kramers - Kronig type to normal waves. In the case of surface waves, analogous disruption of analyticity characterizes the possibility of the emission of surface-wave energy into the volume of the medium.