title: Generation of radially-polarized terahertz pulses for coupling into coaxial waveguides.
abstract: Coaxial waveguides exhibit no dispersion and therefore can serve as an ideal channel for transmission of broadband THz pulses. Implementation of THz coaxial waveguide systems however requires THz beams with radially-polarized distribution. We demonstrate the launching of THz pulses into coaxial waveguides using the effect of THz pulse generation at semiconductor surfaces. We find that the radial transient photo-currents produced upon optical excitation of the surface at normal incidence radiate a THz pulse with the field distribution matching the mode of the coaxial waveguide. In this simple scheme, the optical excitation beam diameter controls the spatial profile of the generated radially-polarized THz pulse and allows us to achieve efficient coupling into the TEM waveguide mode in a hollow coaxial THz waveguide. The TEM quasi-single mode THz waveguide excitation and non-dispersive propagation of a short THz pulse is verified experimentally by time-resolved near-field mapping of the THz field at the waveguide output.
authors.affiliation: School of Physics and Astronomy, University of Birmingham, Birmingham B15 2TT, UK.|Department of Electronic and Electrical Engineering, University College London, Torrington Place, London WC1E 7JE, UK.
authors.forename: Miguel
authors.initials: M
authors.lastname: Navarro-Cía
authors.affiliation: Department of Electronic and Electrical Engineering, University College London, Torrington Place, London WC1E 7JE, UK.
authors.forename: Jiang
authors.initials: J
authors.lastname: Wu
authors.affiliation: Department of Electronic and Electrical Engineering, University College London, Torrington Place, London WC1E 7JE, UK.
authors.forename: Huiyun
authors.initials: H
authors.lastname: Liu
authors.affiliation: Department of Electronic and Electrical Engineering, University College London, Torrington Place, London WC1E 7JE, UK.
authors.forename: Oleg
authors.initials: O
authors.lastname: Mitrofanov