Tapered photoconductive terahertz field probe tip with subwavelength spatial resolution

Abstract

In this work a photoconductive probe tip applicable for near- and far-field measurements in the terahertz frequency regime is demonstrated as a powerful alternative to existing terahertz scanning near-field optical microscopy approaches. The probe tip is based on a triangular-shaped patch of freestanding low-temperature-grown GaAs of only 1.3 μm thickness with a pair of tapered metallic wires on top. Using nonresonant electric field enhancement at the tip of the probing device, 10 μm wide metallic structures are spatially resolved and a bandwidth of 2 THz is demonstrated.

Review of Near-Field Terahertz Measurement Methods and Their Applications

“…Many reasons for such popularity: the recent discovery of the extraordinary transmission of light through subwavelength structures [1], the invention of the near-field scanning optical microscope called NSOM [2,3], or the irrepressible race to break the diffraction limit in order to design and fabricate smaller and smaller structures for the micro (nano)-electronics industry. Other branches of the electromagnetic spectrum are not to be outdone; Terahertz (THz) radiation in particular with its larger wavelength from 30 μm to 2 mm corresponding to a frequency range spanning from 150 GHz to A. J. L. Adam (B) TU Delft, Delft, The Netherlands e-mail: a.j.l.adam@tudelft.nl 10 THz and its properties contain many advantages for those who want to study near-field effects: structures can be done by classical optical lithography; metals like gold can be considered as perfect conductor; dielectric properties can be artificially engineered with the use of doped semi-conductors such as silicon. More important of all, a technique called Terahertz Time Domain Spectroscopy (THz-TDS) allows to measure the time-dependent electric field with an ultra-broad bandwidth, typically a decade or more [4,5].…”

Terahertz diffraction enhanced transparency probed in the near field

“…The transmission measurements are referenced to a quartz substrate. The THz near-field microscope used in these measurements has been described previously [18], where THz microprobes [19] (Protemics GmbH, Germany) are used to measure the near field at a distance of 0.5 μm above the sample. The THz microprobes used in these experiments allow isolation of a specific polarization of the electric near field.…”

THz-TDS using a photoconductive free-space linear tapered slot antenna transmitter

“…Near-field coupling methods have existed for a number of years, although they are commonly found in the form of near-field probes for surface characterization [9][10][11]. The PC-FS-LTSA overcomes many of the issues associated with substrates lens and guided-wave antennas.…”