Extraordinary wave modes in purely imaginary metamaterials beyond the critical angle.

When waves are incident from a high-index medium to a low one, total reflection occurs commonly for the incidence beyond the critical angle. However, this common sense is broken by a purely imaginary metamaterial (PIM), which also supports a real refraction index yet with pure loss and gain elements in their permittivity and permeability. We find that even beyond the critical angle of a lower-index PIM slab, some extraordinary wave modes including laser, anti-laser, perfect attenuator and perfect amplifier can appear. The general conditions of these wave modes are theoretically given out and the underlying mechanisms are revealed. Also, we study the influence of incident polarizations, geometric thickness and the parameters of the PIM slab on these extraordinary wave modes, with more wave propagation behaviors discovered.