Wave-vector Spectrum of Monochromatic Terahertz Surface Plasmon Polaritons on Real Surfaces

Experiments at the Novosibirsk free electron laser demonstrating that monochromatic terahertz surface plasmon-polaritons (SPPs) on a real metal surface have a rather wide-band spectrum of their wave-vector are described. The fact was evidenced by detection of bulk waves radiated from the SPP track and by means of SPPs reflection from a mirror installed normally to the sample surface or tilted to it. The cause of the wave-vector splitting is supposed to be SPPs scattering on imperfections of the surface. This splitting leads to substantial radiative losses of the SPPs, which may be the cause of violation of the 1/ω2 SPP propagation length dependence predicted by the Drude model.