Finite-difference-time-domain Simulation Of Terahertz Pulse Generation And Reshaping

Terahertz (THz) wave is in a very special band in electromagnetic spectrum, which isin microwave and infrared. And it is difficult to generate and control directly by the presentmicrowave and infrared technology. THz wave has the advantages of low photon energy,high resolution and strong transmission capacity, which is widely used in detection,imaging, communications and spectral analysis, and has become the international researchfocus. In some special applications, such as THz time-domain spectroscopy, THz imaging,millimeter and submillimeter wave communications, it require a specific shape and spectralcomponents of the THz pulse. Thus the spatiotemporal shaping of the THz pulse is needed.In this thesis, we numerically simulate the generation of THz pulses by photoconductiveantenna and spatiotemporal shaping of THz pulses by metal slits and holes with finitethickness. These analysis provides a theoretical foundation and calculation methods for theoptimization of photoconductive antenna structure to enhance the power of THz radiationfield and to get THz pulse with specific shapes.A theoretical model of the photoconductive antenna generating THz pulse isestablished. We simulate the spatial distribution of two dimensional (2D) and threedimensional (3D) THz radiation field by employing the FDTD method, and analyze thechanges of the THz radiation field in free space and the internal antenna. Simulation resultsshow that the internal GaAs substrate has a strong confinement effect on THz radiated fieldespecial for higher-frequency components. The spatial distribution of THz field that is bothwithin and outside the photoconductive antenna shows unbalanced and extraordinaryfeatures. THz radiation field energy is mainly concentrated on the photoconductiveantennas gap center, which is far greater than other regions.We also simulate the process of a Gaussian THz pulse transmitted through rectangularaperture and circular aperture of finite thickness by employing3D FDTD domain method.The effect of the thickness and width of the rectangular aperture, the radius and thickness ofthe circular aperture and the slit width on the THz pulse shaping is analyzed. The simulated results show that we can realize effective shaping and filtering of THz pulse usingrectangular and circular conductive apertures of finite thickness. When the long side of therectangular aperture is perpendicular to the polarization direction of the incident wave, therectangular aperture has a good influence on shaping and filtering of THz pulse. While,when the long side of the rectangular aperture is parallel to the polarization direction of theincident wave, it almost has no obvious effect on shaping and filtering of THz pulse.Circular aperture has more obvious effect on shaping of THz pulse than rectangularaperture. With the increase of slit width, slit-shaping role is weak. The shaped THz pulsecan be applied to THz spectroscopy and THz imaging.