Time-domain imaging system in the terahertz range for immovable cultural heritage materials

In the field of cultural heritage science, the use of non-destructive and contact-free techniques has increased sharply over the past 10 years. Compared with conventional spectroscopic and imaging techniques such as X-ray, ultraviolet, infrared, and laser spectroscopy, terahertz time-domain imaging (THz-TDI) is an innovative, non-invasive, and safe technique, which provides good penetration depth (similar to 1 cm) and broad spectral bandwidth (0.1-10 THz). This paper sets out the protocol and methodology for the application of THz-TDI to immovable cultural heritage, illustrated by a series of case studies. The case studies demonstrate the efficacy of the technique in providing structural and material information for conservators.