Loss Characteristics of TeraHertz Surface Waves on Laser Micromachined Textured Metals

For the application of geometrically induced THz surface wave technology for communication and sensing, a critical analysis of the propagation characteristics (i.e., dispersion and attenuation) for different textured surfaces should be studied and benchmarked. For the broadband characterization of archetypal textured surfaces (e.g., corrugated plane, 2-D array of blind holes and bed of nails) supporting THz transverse magnetic (i.e., p-polarized) surface waves, we employ time-domain spectroscopy and edge-diffraction coupling methods. Measurements of laser micromachined prototypes demonstrate strong frequency-dependent dispersion and the large impact that surface roughness of the order of few $\mu$ m has on the path loss, increasing it by a factor ranging from 1.6 to 4.3 compared to smooth textured surfaces. Together with numerical modeling, we disentangle all loss mechanisms (namely, ohmic, scattering, propagation divergence, and phase mismatch) and highlight the challenge of loss estimation due to surface roughness in highly confined THz surface waves.