Investigation of the lowest-order TE mode of the parallel-plate metal waveguide for terahertz pulses

We describe an experimental and theoretical study of the lowest-order transverse-electric (TE₁) mode of the parallel-plate waveguide for the propagation of broadband THz pulses, and demonstrate undistorted THz pulse propagation via the TE₁ mode. This demonstration overcomes two fundamental problems associated with the low-frequency cutoff of this mode, the group velocity dispersion and the spectral filtering, which have prevented the use of this mode for THz wave guiding in the past. We also observe a remarkable counter-intuitive property of the TE₁ mode: its attenuation decreases with increasing frequency. This phenomenon has not been observed with any other THz waveguide to date, and can enable extremely low-loss propagation. In addition, we find that it is possible to achieve almost 100% coupling to the TE₁ mode from an input Gaussian beam. These results favor the use of the TE₁ mode for the efficient guiding of THz pulses.