Coupling of terahertz pulses onto a single metal wire waveguide using milled grooves

We demonstrate a novel approach for coupling freely propagating THz pulses onto a metal wire waveguide utilizing grooves fabricated directly into the metal. Using broadband THz pulses incident on the wire, we use metal segments containing zero, one, three, and eight uniformly spaced grooves to launch surface propagating multi-cycle pulses along the wire. We observe a one-to-one correspondence between the groove number and the number of oscillations in the THz waveform radiated from the end of the waveguide. We further demonstrate that this coupled radiation is radially polarized. Although the cross-sectional parameters of the grooves are identical in the present measurements, alteration of the individual grooves in a controlled manner should allow for arbitrarily shaped THz pulses to be launched on the waveguide.