The potential of THz Microscopy for Non-Destructive Evaluation Applications

TeraHertz (THz) radiation, f = 0.1 to 10 THz, falls between microwave and infrared in the electromagnetic spectrum. This spectral range harbours several key benefits that are relevant for applications in non-destructive evaluation (NDE), namely, many optically opaque materials are transparent for THz, including packaging material, it is non-ionising, and it is a spectral rich fingerprint region for substances found in pharmaceutical and explosive substances. Prominent THz technologies, such as THz time-domain spectroscopy and imaging, are described and their current uses in various industries (safety, aviation and automation, cultural heritage, and food) as an NDE tool are discussed. Despite its potential for NDE applications, one of the challenges faced by THz technologies is its relatively low spatial resolution compared to light technologies. Methods being developed for enhancing the resolution of THz tools such as near-field modalities, and the relevance this could have for non-destructive testing are outlined. In addition, the challenges that must be overcome before these near-field techniques can be incorporated into pre-existing THz NDE tools
are highlighted.