Theoretical And Experimental Study On Transmission Properties Of Microstructured Metallic Grating In THz Frequency Region

With the development of generation and detection of Terahertz radiation, the design and fabrication of the controlling device in THz frequency region become more and more imperative. In the thesis, a candidate device for controlling THz radiation is proposed, which is microstructured metallic grating in THz frequency region. A theoretical and experimental study on the proposed metallic grating is detailed.Based on the fundamental electromagnetic theory, we obtain the field distribution in whole space by applying Floquet-Bloch Theorem and surface impedance boundary condition to the metallic grating exposed to p-polarized electromagnetic wave. Furthermore, we treat the microstructured grating as effective F-P interferometer, then extract the scattering coefficients of both the front and bottom surface of the grating. When the incident wavelength is close to the grating period, the grating exhibits famous Wood anomalies. When the incident wavelength is larger than the grating period, it is demonstrated theoretically that the grating can be considered as a kind of metamaterials with homogenous refractive index equal to the ratio of grating period to the slit width. The surface of such a microstructured grating can support the bond surface mode similar to the Surface Plasmon Polaritons(SPPs). It is shown that the grating exhibits enhanced transmission due to the surface mode. In addition, we have proposed theoretically in the long wavelength region that the microstructured metallic grating with constant period but chirped slit width behaves self-focusing effect.We have used ZnTe-based THz time domain spectroscopy(THz-TDS) to experimentally investigate the nonresonant transmission of the microstructured metallic grating perpendicularly impinged by p-polarized THz radiation pulse. The experimental results agree with the theoretical calculation under the assumption that the nonuniform period of the grating satisfying normal distribution. Meanwhile, the transmission is also measured when the grating is rotated around the axis perpendicular to the grating surface. We have successfully explained the transmission theoretically by employing electric field vector projection and polarization-dependant detection of the ZnTe crystal.