| Terahertz radiation refers to electromagnetic waves with frequencies between 0.1 THZ (0.1×1012Hz) and 10 THz (10×1012Hz), which lies at the boundary between the microwave region and the infrared region. In recent decades, with the rapid development of ultrafast optoelectronics technology and low-scale semiconductor technology, which provide proper source and detection method for terahertz research, terahertz science and technology has witnessed speedy growth. Terahertz spectroscopy technology has been widely used in various aspects of daily lives, due to many advantages of terahertz pulse of being low photon energy, transient, broadband, coherent, and penetration of the non-polar substances.This thesis focused on the following topics:1. The mechanisms of terahertz pulse generation by photoconductive antenna are investigated. The factors that affect the performance of THz radiation are analyzed. The dependence of large-diameter antenna terahertz radiation, including near-field radiation and far field radiation, on pump pulse width, pump pulse energy, bias field amplitude and carrier recombination time are calculated and analyzed. The effect of strong electric field on terahertz radiation is also investigated.2. The electro-optic sampling method for detecting terahertz pulse is studied. The distortion of detected terahertz time-domain waveform, caused by dispersion, absorption, reflection and velocity mismatch, is theoretically analyzed and numerically calculated. According to the calculation, the optimization methods of the detection system based on electro-optic sampling are analyzed. The optimized angle and thickness of crystals as terahertz detectors are given.3. Terahertz wave propagation properties in scattering medium and dispersive media are numerically studied from the aspects of beam shape maintaining and beam energy maintaining. By calculation, the feasibility of terahertz technology applied in harsh environment is illustrated.4. The principle and work process of the terahertz time domain spectroscopy system are investigated. A terahertz time domain spectroscopy system is built. Factors, that impact the system properties, such as terahertz radiation intensity, bandwidth, time resolution, spectral resolution and signal to noise ratio, are analyzed and experimentally studied, and hereby the spectroscopy system is optimized.5. The amoxicillin's terahertz spectra are measured. Tablets of amoxicillin drugs are manufactured. Data processing method of terahertz time domain spectroscopy experimental results is derived. Transmission spectra and absorption coefficient curve of the drugs are obtained. The reliability of the system is proved. Factors that affect the absorption spectra are analyzed. Through analysis, we found that 1.32THz and 1.52THz absorption peak can be used as the characteristic absorption peak of amoxicillin, to realize the sample identification in general conditions, even harsh conditions.6. The idea of using terahertz technology to detect aging explosives is proposed. The disadvantages of the existing aging explosives detection methods are pointed out. The feasibility, safety and practicality of terahertz time domain spectroscopy used for aging explosive detection are analyzed and demonstrated. |
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