Investigation of terahertz Sommerfeld wave propagation along conical metal wire

The waveguide properties of a terahertz wave propagating along conical metal wire have been investigated under the framework of the Sommerfeld model. The effects of composed materials, metal wire diameter, and temperature on the waveguide characteristics have been shown and discussed. The numerical calculation agrees well with the experimental results shown by Ji et al., and it predicts that a metal wire waveguide shows better propagation properties at lower temperature. The ratio of energy density contours demonstrate that energy concentration at the end-tip increases with the decreasing of frequency, end-tip diameter, and radial distance from metal wire surface. As the temperature decreases, the local field intensity increases, which may result from the higher conductivity and smaller skin depth of metal at lower temperature. Because the energy density is very sensitive to temperature, the conical metal wire tip can be used to measure the changes of temperature accurately, which may be confirmed by experiment in the future. (C) 2009 Optical Society of America