Research On Optical Rectification Generation Of Terahertz Radiation And Terahertz Time-domain Spectroscopy Of Riboflavin

Terahertz sources and terahertz time-domain spectra are two important fields in terahertz technology. we have built up a terahertz time-domain spectral system and combine with the quantum chemical calculations to analyse absorption spectral of terahertz time-domain of riboflavin.Chapter one introduces the characters of terahertz radiation, expatiates on terahertz sources and development history of probe technology of technology radiation, and introduces applications of terahertz radiation briefly. Terahertz time-domain spectroscopy technology can be applied for assignment of identification qualitatively; terahertz image technology can be applied for security checking and military application.We study methods of generation and probe of terahertz radiation in the chapter two. It introduces the most commonly methods of generation of terahertz radiation: photoconduction and optical rectification. Different antenna structures have different terahertz radiation in the system of generation of terahertz radiation by photoconduction. Characteristic parameters of photoconduction material determines energy and frequency spectrum of terahertz radiation. We explain the theory of terahertz radiation by photoconduction, optical rectification is one of the most popular methods which generates terahertz radiation by crystals non-linear effect. Intensity of terahertz radiation is in dependence on intensity of laser. It has two major methods for probing terahertz radiation, one is photoconduction sampling, the other is free space electro- optic sampling. Detecting terahertz radiation by photoconduction sampling is reversible with generating terahertz radiation. Detecting range is narrow by photoconduction sampling. We introduce the theory on free space electro-optic sampling. Terahertz radiation makes isotropic electro-optical crystal in optics characteristic, it makes probe beam's phase delayed when probe beam passes the electro-optical crystal. So we get the amplitude information of terahertz radiation, detecting range is very wide by free space electro-optic sampling. We introduce the methods of generation and detection of terahertz radiation. We have built a set of system with generation by optical rectification and detection by free space electro-optic sampling. Parameters of laser we used: wave length 800nm, repetition frequency 1 KHz, pulse width 100fs. Generation crystal is GaAs(110)and detection crystal is ZnTe(110); Frequency spectrum of terahertz radiation can reach 2.5THz.We study the research on terahertz radiation by optical rectification and detection by free space electro-optic sampling. Meanwhile, we also calculate the terahertz radiation in different pulse width.Chapter three introduces the terahertz time-domain spectrum of riboflavin. We analyse the absorption of riboflavin at the 0.5-2THz.The absorption positions of riboflavin locate at 1.036THz,1.179THz,1.364 THz,1.519THz,1.910 THz. We also analyse the refractive index in this range, it is about 1.4. At last.The low frequency infrared spectra of riboflavin is calculated with DFT method and theoretical values accord with experimental datas well.