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The frequency range of the electromagnetic spectrum known as the teraHertz (THz) regime (100 GHz to 10 THz) has drawn considerable interest in the research and development community in the last two decades as methods, electrical and optical, have been developed that provide easier access to these frequencies^[1]. Most dielectric materials are transparent to THz radiation, while metals are opaque. This alone makes THz an attractive technology for security and manufacturing-inspection applications. In fact, NASA employs THz imaging to inspect the sprayed-on-foam used on the space shuttle's external tank. Unlike X-ray-based technologies, THz is much safer due to its non-ionizing nature.

Many solids, liquids and gases exhibit unique spectroscopic “fingerprints” at THz frequencies. THz time-domain spectroscopy can yield information about a material's refractive index and absorption over a broad bandwidth of frequencies. The conductivity and mobility of many semiconductor systems has been characterized using this technique. It has been shown that THz can be used to distinguish between benign and malignant human tissue. Many explosives and illegal drugs also exhibit unique identifying THz spectra. The ability to simultaneously conduct imaging and spectroscopy has drawn interest for many possible applications with security, inspection and biomedical spectroscopy being just a few.

The lack of effective waveguides has been a significant hurdle to the development of THz-based applications. Most THz systems are large and difficult to use because they rely on free-space optics to guide and manipulate the THz pulses. This requires users to be well experienced with optical-alignment techniques and also direct line-of-sight access to the area or sample of interest. Waveguide engineering at THz frequencies is difficult. This article outlines the requirements for effective THz waveguides, explains a recent solution to this engineering dilemma, and shows how finite element method (FEM) modeling is being used to develop an effective and efficient THz waveguide system.

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