Terahertz Time-Domain Spectroscopy Of Amino Acids

Terahertz(THz) radiation, which occupies a large portion of the electromagnetics in the range between the far-infrared and microwave region,generally be defined between 0.1 THz and 10 THz. Radiation of 1 THz corresponds to the wavelength of 300μm,the wave number of 33.3 cm-1,the single photon energy of 4.1 meV,and the eigen temperature of 48 K. Due to these characters, terahertz technique plays important role in the fields such as studies of molecule vibrational-rotational spectrum, lossless detection, imaging by transmission, and so on. However, be enslaved to the difficulty of terahertz sources, research of terahertz techniques is far less than these spectroscopic techniques in other electromagnetic region.Chapter one introduces the origin of spectroscopy,the general situation and characters of THz radiation. The development process and research actualities of THz radiation at home and abroad are also described.In Chapter two, the nonlinear characters of medium is introduced, two production methods of THz radiation (optical rectification and photoconduction) are theoretically explained, and two detection methods (photoconductive sampling and free-space-electro-optic sampling) are also illuminated.In Chapter three, we especially emphasize the THz experimental set up and make a detailed statement of the experimental operation in our laboratory. A signal of THz radiation experimentally measured is also simply analyzed.In Chapter four,the terahertz spectra (0.5-2.5THz) of eleven amino acids have been measured using THz time-domain spectroscopy. Their vibrational-rotational spectra in terahertz region have also been calculated and analyzed based on a use of the software Gaussion 03 and Gaussion view, under DFT method with different basis sets(HF and 3-21G, B3LYP and 6-311G**). The terahertz spectral lines obtained are analyzed, assigned and confirmed. Among them four new spectral lines are confirmed to be discovered.Chapter five summarizes the whole work, including the key experimental parameters and theoretical methods, experimental results and theoretical results. Finally we make a conclusion for our present work and an expectation for future studies.