Terahertz spectroscopy and imaging – Modern techniques and applications

Abstract

Over the past three decades a new spectroscopic technique with unique possibilities has emerged. Based on coherent and time-resolved detection of the electric field of ultrashort radiation bursts in the far-infrared, this technique has become known as terahertz time-domain spectroscopy (THz-TDS). In this review article the authors describe the technique in its various implementations for static and time-resolved spectroscopy, and illustrate the performance of the technique with recent examples from solid-state physics and physical chemistry as well as aqueous chemistry. Examples from other fields of research, where THz spectroscopic techniques have proven to be useful research tools, and the potential for industrial applications of THz spectroscopic and imaging techniques are discussed.

Graphene hyperlens for terahertz radiation

“…[1][2][3] The natural diffraction limit, however, restricts the resolution of the standard THz imaging systems to about a wavelength, which is relatively large (300 μm in the free space at 1 THz). To overcome this restriction one can use scanning near-field THz microscopy that allows for even submicrometer resolution in the scattering (apertureless) configuration, 4 but such a technique is slow.…”

“…The input and output periods, widths, and radii were chosen as P in = 200 nm, P out = 600 nm, W in = 40 nm, W out = 120 nm, R in = 15.12 μm, and R out = 45.36 μm, respectively. The radii are selected to satisfy the Fabry-Pérot resonant condition (2). The layers of structured graphene are assumed to be periodic in the direction perpendicular to the image plane (period a y = 50 nm).…”

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].…”

Three-dimensional nanoscale imaging by plasmonic Brownian microscopy

“…On the other hand, electron microscopy allows wide-field 3D imaging of nanoscale structures at higher speed but often requires vacuum environment with limited imaging penetration due to electron scattering. Optical tomography and time reversal technique may be an alternative wide-field 3D imaging method, yet exhibit lower spatial resolution in microns due to the diffraction limit [10][11][12]. Plasmonic superlens [13][14][15][16] enables super-resolution optical imaging beyond the diffraction limit but only provides two-dimensional imaging at a smaller area [17].…”