Research On Maize Seeds And Illicit Drugs With Terahertz Time-Domain Spectroscopy

The terahertz (THz, 1012Hz) spectral 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) is an extremely promising coherent technique since some new characteristics are observed in THz frequency region. The temporal waveform of THz pulse is recorded by electro-optical or photoconductive sampling straight in time domain. By fast Fourier transform operation, the information of amplitude and phase of the THz wave are obtained in frequency domain. THz-TDS provides a direct measurement of the THz electric field, and the complex dielectric constant of a sample is directly extracted by Fourier transform.What make THz waves interesting are that there are possible applications because of their interesting properties. They are less harmful than X-rays when used for medical imaging, and when used for spectroscopy they provide information other waves cannot. 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.In this paper, researches in two hotspot fields, biomedicine and chemistry, have been done.I. In biomedicine, investigations on maize seeds have been done as follows:1. To realize the selection and identification of different maize seeds, some samples such as powders, embryos and deoxyribonucleic acids (DNA) of different maize seeds have been measured with THz-TDS. In the experiment, the samples are prepared more subtly and difficultly gradually to obtain the characteristic "fingerprint" absorption spectra of maize seeds in THz band.2. To assure the feasibility and validity of DNA extraction method, two different DNA extracting methods are used and the respective influence on experimental result of them is investigated.3. To assure the feasibility of sample preparation method, samples are obtained by using two different sample preparation methods and the respective influence on experimental result is studied.II. In chemistry, investigations on some series of illicit drugs have been done as follows:1. To obtain illicit drugs' characteristic "fingerprint" spectra in THz band, their THz time-domain spectra are measured after the illicit drugs are classified which are provided by the First Research Institute of Ministry of Public Security of China. Our work has provided an experimental basis for inspection and detection of illicit drugs with THz-TDS. A lot of preparatory work for establishing "fingerprint database" of illicit drugs has been done.2. Some spectra of illicit drugs samples are obtained theoretically by quantum chemistry calculation. To explain the experimental curves with related physics theories, some relatively ideal theoretical curves are obtained when the appropriate calculation base group has been selected.