| This thesis presents the research level and production about THz waves technology inside and outside. What is the powerful technique of THz time-domain spectroscopy (THz-TDS) with this technique both of intension of electric field and phase message are measured. Consequently via Fourier transform of the input pulse and the propagated pulse, the frequency dependent absorption coefficients and refractive index of the samples can be obtained well and truly.Especially terahertz time-domain spectroscopy used in this work is a photoconductive switching of transmitter and receiver which are gated by femtosecond optical pulses and the system is aligned into an 8-F confocal geometry with four parabolic mirrors in which is at Ultrafast Terahertz Optics Lab (UTOL) in Oklahoma State University (OSU) . Have studied some spectroscopy characterized about three typical samples by the system respectively and equally use for reference simple effective theory in conjunction allows to demonstrating and calculating. There have been some valuable signatures of these samples by terahertz time-domain spectroscopy.Lately, terahertz time-domain spectroscopy is newly technology to study in biological tissues significance, genetic analysis and cancer diagnosis. Owing to the biological tissues with high level of hydration show strong absorption at terahertz frequencies, the results present here highlight terahertz time-domain spectroscopy characterization of various animal tissues obtained from pork and rats, include skin, fat and lean. The experimental data indicate different frequency-dependent response to terahertz radiation due to these difference surface layers from two kind animals. The same type tissue from different animals, however, is observed to show very similar water absorption.Zinc oxide (ZnO) is an excellent II-VI compound semiconductor so it has widely range application. Optical and dielectric properties of ZnO tetrapod structures have been detected where the real and imaginary parts of dielectric functions are different frequency-dependent response to radiation terahertz. And illustrate the measured compare with ZnO nanowires structures. It shows that the terahertz spectrum of the single-crystal ZnO is also dominated by the Ei(TO) phonon mode centered at the frequency of 12.41 THz. In the low-frequency dielectric properties of ZnO tetrapods is found to be associated with the transverse optical Ei phonon mode, which corresponds well to that of the bulk ZnO. The ZnO tetrapods show the similar low-frequency optical characteristics with that of the bulk ZnO.Respectively with theory and experiment, we have studied the enhanced transmission efficiency phenomenon of THz pulse through in periodically patterned subwavelength holes arrays made from metals. To investigate the extraordinary THz transmission in terms of dielectric properties of metals at different resonance frequencies, we prepared two types of metallic arrays: Metal- silicon samples (M-Si) and metal-air samples (M-A). The samples were lithographically fabricated on silicon wafer where optically thick metal layer of Ag, Al, and Pb, respectively were made from good and poor electrical conductors for Ag, Al, and Pb by thermal evaporation, for which the dielectric function follows the Drude model. Extraordinary THz pulse transmission characterized was measured in subwavelength metallic hole arrays by Terahertz time-domain spectroscopy. Experiments present results of resonance excitation of surface plasma polaritons (SPPs) at the metal-dielectric interfaces in THz ranges, so as to enhanced transmission efficiency of THz electromagnetic waves. SPPs-enhanced transmission depends only on dielectric properties. The metal complex dielectric function is key role in SPP-enhanced transmission.
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