Close-up of a waveguide device that "couples" terahertz radiation, moving it from one wire-like waveguide to another. The device is fabricated on a piece of stainless steel foil. Terahertz radiation is beamed onto the foil within the semicircular etching, which focuses the radiation and sends it down the lower waveguide (the lower part of the "X" shape). Where the two waveguides come near each other (the elongated middle of the "X"), half the radiation jumps from one waveguide to another, so half the radiation comes out of the right-side end of each waveguide. Each waveguide is made of numerous small rectangular punctures in the foil. The penny is for scale.