Terahertz Spectroscopy In Food Safety Applications

The terahertz waves (1THz = 1012Hz), sandwiched between microwaves and far infrared light waves, have the frequencies between 0.1THz and 10THz. In the last few decades, the rapid progress of ultrafast laser technology has promoted the study of the theory and applications of terahertz generation and detection technology. Terahertz waves have many attractive characteristics which can not be achieved in other electromagnetic range. Because of these properties, it was believed that terahertz technology has a good future in many different fields, such as physics, chemistry, biology medicine, communication, radar, security inspection, quality control. In this thesis, using terahertz spectroscopy technology, we detect poison or harmful material which is risk for adding in foods and proposes the way to determine the concentration of them using the terahertz spectroscopy. The main works are summarized as follows:In the first chapter, the importance of food safety and characteristic of terahertz wave were summarized. The development of terahertz spectroscopy technology in recent year was concluded. It is demonstrated that the terahertz technology has advantages for food safety inspection.The generation and detection of terahertz wave were introduced in the chapter two. A transmission terahertz time-domain spectroscopy (THz-TDS) and a reflection THz-TDS experiment system have been built. The optimization of the system was also described in detail.In the chapter three, the melamine and its mixture with polyethylene and milk powder in different consistence were measured using the transmission THz-TDS. In the absorption spectrum, two peaks at 1.99THz and 2.29THz have been obtained. Based on the Lambert-Beer law, the absorption coefficient and the consistence of the melamine in the mixture are determined. Based on the density functional theory, the absorption of melamine was simulated using the DMol3 software and the vibrancy was explained. The simulation result agrees with the experiment data well.In the chapter four, Aqueous solution of two kinds of pesticides which were Pyridaben and Hexaflumuron were measured using a new terahertz reflection TDS system. A series of reflectivity spectra of agricultural chemical solution were obtained. The relation between reflection ratio and concentration of the solution was drawn. A new method for measuring the concentration of agricultural chemical solution with terahertz reflection TDS was proposed. This method is expected to be used in the environmental pollution monitoring and manufacture quality controlling.The last chapter concludes the works presented in this thesis and points out the future works in this subject.