Study Of Terahertz Time Domain Spectroscopy System And Its Applications

Terahertz (THz) technology is a new rising spectrum sensing and imaging technique over these years. Terahertz wave have many attractive characteristics like high penetrability, safety and spectral resolution ability. It is believed that THz technique has a good future in the fields of biological medicine, security inspection, communication and radar, etc. Using THz time domain spectroscopy system, we can do THz spectrum sensing and THz imaging. The THz time domain spectroscopy system has become one of the most promising applications in the THz science and technology.This thesis mainly focus on two important fields of THz time domain spectrum technique-setting up technique of THz time domain spectroscopy system and its spectrum sensing and imaging applications. On the other hand, we analysis some key issues in theory and experimental aspects.The main work and results are listed as follows:(1) One set of THz time domain spectroscopy system has been established, which utilizes a ZnTe crystal as emitter and using a second ZnTe crystal as detector. Approaches for establishing and optimizing are clearly introduced. The related software used to operate this system has been designed in Lab VIEW environment. The structure of the program is described. Building and optimizing method directly decide the system's experiment performance; it is believed to have certain significance for Terahertz spectrum researchers.(2) Evaluate the system's property, signal to noise ratio, dynamic range and repetitiveness; discuss the source of noise. The THz wave beam width is measured using knife edge slit method. The results show the signal to noise ratio is above 1000:1, the dynamic range is 5400. The signal to noise ratio in 0.2-2.2THz is higher than it in other frequency fields. The overall stability is good. The position where samples are usually placed is determined. The results show that the shape of THz beam flare at the focus point is not a circle; the diameter of THz beam at this position is 4.357mm at horizontal directions and 4.502mm in vertical direction respectively, the eccentricity is 0.26. Our system's performance parameter is as good as that in Beijing Normal University Terahertz Lab, the system SNR has reached the same order, but our dynamic range and beam radius are a little weak. These results have reference values to our future terahertz wave spectrum measurement and imaging experiments.(3) Utilizing our THz time domain spectroscopy system, we have done some spectrum sensing and imaging experiments. In spectrum sensing, spectrum of the air, nitrogen, z cut quartz and water are measured. Experiment got the refractive index of z cut quartz and water. The water absorption index comparison of our experimental data and reported data shows our results in 0.2-2.2THz are reliable. In imaging experiment, by point by point scanning, hoops in different thickness cardboard are successfully detected. We compared different data processing methods, results show the image quantity is strongly relying on the data processing method. Also, it verifies our system's good performance in terahertz spectrum sensing and imaging and its applications in security detecting abilities.In short, this paper has many detailed and comprehensive analysis and exploration to terahertz time domain spectroscopy technique. Not only are the key problems of system building, also the research thoughts and methods in applications discussed. It has certain directive significance on future exploration of terahertz time spectrum techniques.