Terahertz Spectroscopic Investigation Of Explosive And Contamination

Terahertz (THz) radiation with a frequency range of 0.1～10 THz, sandwiched between microwave and infrared, belongs to far infrared region. THz imaging and sensing technologies can provide information not available through conventional methods such as microwave and X-ray techniques. In the last decade, rapid progress in ultrafast laser technology and semiconductor material technology provides a steady and reliable optical source for the THz pulses generation, which greatly promotes the research in the THz waveband that is difficult to access before. THz time-domain spectroscopy (THz-TDS), as a newly technique of THz technology, has been widely used in the sensing and imaging field since it has the advantage of insensitive to the thermal background and high signal-to-noise ratio comparing with the traditional Fourier transform infrared spectroscopy (FTIR).Chapter one introduces the existing detection techniques for safety inspection and the advantages of THz technology as a potential tool in inspecting explosive and contamination. The status quo of investigations by using THz technology was summarized. Our motivation and the signification for start this thesis was presented.Chapter two is a summary of existing systems of THz-TDS especially emphasized on the transmitting system and corresponding methods for extracting optical parameters. The principle of optical path which built by our laboratory was presented in detail including measurement conditions and sample preparations.Chapter three illustrates the experimental results of explosive and contamination by using THz-TDS. The comparison of THz spectra for five explosives was presented. The absorption coefficient and refractive index of these materials were obtained. The results show that the absorption was increased with the frequency increasing for TNT sample while the other samples all have characteristic absorption peaks in the range between 0.2 and 2.6 THz. In addition, THz spectrum of HNIW was reported for the first time. The absorption peaks we obtained agree with the literature. These results demonstrated that THz-TDS has the potential for explosive identification and safety inspection application.The contaminations of nitro aniline isomers and azobenzene were studied in 0.2～2.6 THz region. The results show that THz-TDS is sensitive to the isomers. Different nitro-aniline...