Design and test of wide-band terahertz dielectric sub-wavelength focusing probes

This manuscript presents two new wide-band terahertz (THz) dielectric sub-wavelength focusing probes for near-field measurements. The first design is characterized by being axially symmetric (conical) while the second is a rectangular based design (pyramidal). The axially symmetric design is specialized for doing spectroscopy and imaging due to its wideband and sub-wavelength focusing resolution. The rectangular design is characterized by its ability to preserve polarization. It will find applications in probing of terahertz planar devices and in polarization sensing and imaging. The probes have a wide bandwidth scanning approximately 0.1-1 THz. The probes were fabricated from low-loss high-density polyethylene. The axially symmetric probe has a sub-wavelength focusing resolution ranging from one fifth of a wavelength up to half a wavelength in a frequency band of about 150 GHz. In this paper, the design and properties of these two probes are presented. Applications of these probes are demonstrated by sub-wavelength near-field imaging, spectroscopy and probing of planar circuits.