Reflection of terahertz monochromatic surface plasmon-polaritons by a plane mirror

Using a free electron laser developed in Novosibirsk, we have studied the reflection of monochromatic (λ = 130 μm) surface plasmon-polaritons (SPPs) from a plane mirror attached to a waveguiding surface. It is found that 100 % SPP reflection occurs not only in the perpendicular position of the mirror relative to the surface, but also when the mirror is deflected from the normal by the angle α being smaller than the limiting angle α∗ proportional to the SPP wave vector. When the mirror is deflected by the angle greater than α∗, SPPs on a perfectly smooth surface must transform into a bulk wave, while, in the experiment, the SPP reflection coefficient decreases gradually to zero with increasing α, which is a manifestation of dispersion of the wave vector of monochromatic SPPs, caused by their scattering on the inhomogeneities of a real surface.