Abstract
The terahertz spectral range (frequencies of 0.1–10 THz) has recently emerged as the next frontier in non-destructive imaging and sensing. Here, we review amplitude-based and phase-based sensing modalities in the context of the surface wave enhanced sensing in the terahertz frequency band. A variety of surface waves are considered including surface plasmon polaritons on metals, semiconductors, and zero gap materials, surface phonon polaritons on polaritonic materials, Zenneck waves on high-k dielectrics, as well as spoof surface plasmons and spoof Zenneck waves on structured interfaces. Special attention is paid to the trade-off between surface wave localization and sensor sensitivity. Furthermore, a detailed theoretical analysis of the surface wave optical properties as well as the sensitivity of sensors based on such waves is supplemented with many examples related to naturally occurring and artificial materials. We believe our review can be of interest to scientists pursuing research in novel high-performance sensor designs operating at frequencies beyond the visible/IR band.
Highlights
The extreme spatial confinement of surface plasmon polaritons (SPPs) in the visible spectral range has led to a revolution in sensing [1]
Material losses cannot ignored as imaginary part of the material dielectric constant can be comparable or larger than its be ignored as imaginary part of the material dielectric constant can be comparable or larger than its real
Lossy High-k Dielectrics In Section 3.4 we demonstrated that a well-defined surface wave can propagate at the surface of a lossy high-k dielectric
Summary
The extreme spatial confinement of surface plasmon polaritons (SPPs) in the visible spectral range has led to a revolution in sensing [1]. Plasmonic waves propagate along the metal/dielectric interface, featuring a deeply sub-wavelength (100 nm–1 μm) modal size [2,3,4], and optical properties that are highly sensitive to changes in the refractive index or geometrical structure of the analyte in the direct vicinity of the metal surface. These properties make surface plasmon polaritons ideal for high-sensitivity surface sensing applications and characterization of deeply sub-micron-sized objects (such as proteins, cell organelles, viruses, etc.) that have been immobilized or captured at the metal surface [5]. Key advantages when operating in the THz band are the ability to detect the complex electric field of THz waves (phase and amplitude), availability of both pulsed (sub-1 ps) and continuous wave (CW) THz systems, as well as ability of conducting dynamic measurements with sub-1 ms temporal resolution [6]
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