Frequency-dependent circular-polarization of terahertz chiral spoof surface plasmon polariton on helically grooved metallic wire

Chiral spoof surface plasmon polaritons in the terahertz region, resulting from a coherent superposition of TM and HE modes, can be generated by normally exciting helically corrugated metal wire with a linearly polarized Gaussian light. The handedness of the chiral SPP depends on the handedness of the helical groove. The chirality of the surface wave causes a spiral spatial extent of average power whose period is determined by the difference in the wave vector between two modes. Simultaneously, highly circular polarization of a confined surface wave emerges from the chirality of the geometry. Moreover, the polarization state is heavily dependent on working frequency relative to the characteristic frequency of each mode. This type of chiral SPP, originating from the helical groove, makes helically corrugated metal wire useful for some special applications, such as circularly polarized sources for terahertz near-field microscopy or terahertz sensors for chiral biomolecules.