Abstract：Terahertz timedomain spectroscopy is a new nondestructive detection technique, which uses the property of low power of terahertz wave, and the characteristics of strong dispersion and absorption of the vibrational transitions and rotations of most biomolecules are shown in this frequency band. These make it possible,to have nondestructive detection and the study of biological activities. In this work, transmission and reflection of terahertz timedomain systems were respectively used to carry out testing melatonin tablets with different mass ratio, and analysis of its spectral properties in terahertz band were also given. It could be concluded that it had characteristic absorption peak at 0.29, 0.50, 0.70, 0.91, 1.20, 2.17 and 2.55 THz. The intensity of the frequency spectrum has a linear relation with the concentration of the sample. In addition, Gaussian 09 and Gaussian VIEW software were used to perform simulation, and the characteristic absorption peaks of melatonin in 0.46, 0.91, 1.15, 2.01, 2.23 and 2.61 THz were acquired, which provided a strong support for experiment results. All these works are the basis and reference for the detection and identification of biochemical samples such as melatonin.
