Applications Of Terahertz Technology In Identification Of Illicit Drugs And Maize Seeds

Terahertz (THz) waves are those with frequencies between 100 GHz to 10 THz. With the location of the spectrum between the electronic and photonic domains, THz waves contain rich information involved in molecular vibaration and rotation, and have sub-picosecond pulse width, low photon energy and high space-time coherence. These unique features are indeed tremendous and imply astonishing applications in warious areas of science such as astronomy, biology, communications and computers. During recent 20 years, rapid progress in ultrafast laser technology provides a steady and reliable optical source for the THz pulses generation, which greatly promoted the development covering THz generation, detection and application. THz imaging, one of the most promising techniques, has attracted more and more attention for material distinguishing and non-destructive inspection. Comparing with the microwave, X-ray and nuclear magnetic resonance imaging, THz imaging can gain spectroscopic information along with the structural information. In addition, the low photon energy and strong penetrability of THz source make the non-destructive inspection and identification feasible, which is not possible using conventional analytical method of chemistry, infrared spectrum and visible light spectrum.Based on the above reasons, researches in this paper are made as follows: First, the identification of maize seeds with THz imaging. The results obtained again with terahertz time-domain spectroscopy (THz -TDS) indicated that there have no obvious absorption peaks and it is not possible to identify using "characteristic fringerprint spectra" technique. Therefore, we demonstrated an advanced THz imaging technique for identification of maize seeds by introducing the component spatial pattern analysis in this paper. The results showed that the identification is realized successfully as long as the data of image and absorption spectral information of samples are known and no specific features of samples spectra were required. Second, the detection and identification of illicit drugs with THz imaging. As an explanation, the characteristic fingerprint spectra and refractive index of Ketamine were first measured with THz -TDS both in the ambient air and in the nitrogen. The results obtained in the nitrogen indicated that there have obvious absorption peaks and it is feasible to detect illicit drugs using "characteristic fingerprint spectra" technique, while the results obtained in the ambient air...