Broadband terahertz time-domain spectroscopy and fast FMCW imaging: Principle and applications
Shen Yao-Chun, Yang Xing-Yu, Zhang Zi-Jian
       

Cross-sectional images and A-scans acquired using the system. (a) An empty cardboard box showing its front and back, (b) a metal pot with a curved surface behind a piece of cardboard, and (c) multiple metal pieces at different depths behind a piece of cardboard.