Experimental And Theoretical Study Of Aromatic Compound In THz Range

Terahertz(THz) radiation is commonly defined by the frequency range of 0.1 to 10 THz. A coherent electromagnetic pulse in the range between the far-infrared and microwave region is used as a detection source. The amplitude of the wave is recorded by electro-optical or photoconductive sampling. Through fast Fourier transform, the amplitude and phase of the wave is given, and then the complex refractive index standing for the absorption and dispersion of the material in THz region is derived. This technique is named as THz time-domain spectroscopy(THz-TDS).THz spectroscopy for a material contains rich physical and chemical information, and consequently Microscopic dynamical processes interactively between material and THz would be in-depth researched. Compared with the previous treatment, THz-TDS is simpler, more reliable, and more precise.Although THz-TDS has been developed for more than ten years and several different methods for generation and detection of the THz electric field turned up, photoconduction and optical rectification are adapted to THz-TDS in laboratory. Firstly, this paper gives a brief description of development process and research actualities of THz radiation. Secondly, chapter 2 introduces an ultrafast dynamics in the semiconductor under an ultrashort laser, some key techniques in femtosecond laser system are surveyed. Furthermore photoconduction and optical rectification are theoretically explained, and two detection methods, photoconductive sampling and free-space-electro-optic sampling, are illuminated. Subsequently we show discrete Fourier transform used in our data treatment. Thirdly, chapter 3 is idiographic experiment work. In this chapter we display our experimental device and make a detailed statement of experimental operation. Some controllable factors that have an effect on THz electric field are also analyzed. And in chapter 4, how to gain the sample optical constants from THz-TDS is our work focus. The terahertz spectra of phenylalanine,m-Toluic and benzoic acid have been measured using THz time-domain spectroscopy. The low frequency vibrational modes of samples are discussed based on the quantum chemical calculations. We interpret tentatively the origin of the observed resonances absorption peaks.Finally, we summarize our experiment work and bring forward our future plan.