Review of Near-Field Terahertz Measurement Methods and Their Applications

Abstract

In the last decades, many research teams working at Terahertz frequencies focused their efforts on surpassing the diffraction limit. Numerous techniques have been investigated, combining methods existing at optic wavelength with THz system such as Time Domain Spectroscopy. The actual development led on one side to a resolution as high as λ/3000 and one the other side to a video-rate recording. The purpose of this paper is to give an overview of the history of the field, to describe the different approaches, to give examples of existing applications and to draw the perspective for this research area.

Enhanced terahertz emission by coherent optical absorption in ultrathin semiconductor films on metals

“…Ultrafast photoexcitation of semiconductor materials is a commonly used technique to generate broadband terahertz (THz) pulses for imaging and spectroscopy applications [1][2][3]. THz pulses can be generated from both semiconductor surfaces and from semiconductor/metal interfaces, where a depletion field is present [4][5][6].…”

Optically controlled terahertz filter based on graphene and cross-like metasurface

“…Radiation in this frequency range is nonionizing in nature and easily passes through the majority of dielectrics, but is strongly absorbed by conductors and some dielectrics. These properties allow the use THz radiation in spectroscopy [1], near-field microscopy [2], scanning security systems, and also in medicine (for example, in the tomography which can visualize layers of the body up to several cm in depth) and in communications systems. A huge incentive for the creation of devices to control THz radiation is that doing so would allow the application of this radiation in many directions, including the field of the THz communications [3].…”

Review of Terahertz Tomography Techniques

“…Now scientists are able to propose optimized solutions of terahertz imaging for a given application with an optimal setup configuration [35] (e.g. pulsed or continuous generator, broadband versus narrowband, spectral resolution versus temporal resolution, active versus passive imaging [36], but also near field [37][38][39][40], wave guiding [41], detectors array and even more camera [42], etc. ).…”