Coupling structures for terahertz near-field microspectroscopy

Near-field optical elements for free space focussing of terahertz (THz) radiation were studied using analytical and numerical approaches for conical waveguides. One of the most promising candidates, a self-similar logarithmic periodical coupling structure (LPCS) embedded into a conical parabolic waveguide, was further experimentally studied with respect to spectral transmission losses using a scaled model at GHz frequencies. Since both studies confirmed the expected broadband high transmission properties of LPCS structures compared to conventional conical waveguides, a prototype structure for THz frequencies as realized by a X-ray lithography technique is presented.