“…THz waves are defined as the electromagnetic waves ranging roughly from 0.1 to 10 THz (wavelengths of 3 mm to 30 μm). The range of potential applications is likely to increase as absorption spectra (i.e., fingerprint spectra) of specific chemicals in the THz-wave region are obtained, including those of illicit drugs, vitamins, sugars, pigments, pharmaceuticals, and agricultural chemicals [1,2,3]. In the THz-frequency range, water is extremely absorptive with an absorption coefficient at 1 THz of approximately 200 cm −1 , which is 10 5 times higher than that in the visible region [4].…”