Terahertz Spectroscopic Investigation Of Explosives

The terahertz (THz, 1012Hz) region, which occupies an extremely large portion between the infrared and microwave bands, belongs to far-infrared band. It is very important to study the characters of materials in THz region since it contains rich physical and chemical information. THz time-domain spectroscopy (THz-TDS) which developed in the 1980's, is an extremely promising coherent technique since it has the advantages of high signal to noise ratio, doesn't need low temperature instrument and so on. What make THz waves interesting are that the collective nature modes of most bio-molecules are located in THz range and there are possible applications because of their interesting properties. Especially, it has attracted more and more attention in nondestructive inspection and detection in biomedicine and chemistry since THz radiation itself has low energy and strong penetrability. Experimental measurement and theoretical analysis of THz spectrum for explosives are introduced based on these properties in this thesis.Chapter one introduces background of the thesis, analyzes THz generation, detection, character, THz technology and significance of the thesis.Chapter two is the THz-TDS technology. Extraction method of related material parameters is explained.Chapter three is the investigation of THz spectroscopy of explosives. experimental measurement and theoretical analysis of THz spectrum for four pure materials and some mixed explosive samples are introduced. The refractive index and absorption coefficient of the samples are measured in the region of 0.2–2.5 terahertz by time-domain spectroscopy ( THz-TDS ) . The absorption spectra are obtained correspondingly. The obtained results indicate the THz-TDS technology can identify the different explosives and roughly analyse the main ingredients of the mixed samples.Chapter four is vibrational spectrum of investigation of THz spectroscopy of explosives . At first, the classification, qualification and characteristic of infrared spectrum, and the frequency calculation introduction of Gaussian 03 software was presented in detail, including theoretical method choice, basis sets choice and process of calculation. The application of Gaussian in simulation of THz spectra was introduced comprehensive; Second, simulation of THz absorbance spectroscopy for different explosives (RDX,HMX,TNPG,PETN) using Gaussian program; And the comparison of THz simulation spectra of explosives using Gaussian and DMol3.At last, the summary of this chapter is introduced.Chapter five is the summary of the thesis. The horizons and hurdles of THz technology in the security inspection were discussed.