Conventional textbook treatments on electromagnetic wave propagation consider the induced charge and current densities as “bound” and therefore absorb them into a refractive index. In principle, it must also be possible to treat the medium as vacuum but with explicit charge and current densities, thus giving a more direct, physical description. However, since the induced waves propagate in vacuum in this picture, it is not straightforward to reconcile that the wavelength becomes different compared to that in vacuum. We provide an explanation for this phenomenon, including associated time-domain simulations. As an extra bonus, the results turn out to illuminate the behavior of metamaterials.

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