Abstract
In this thesis, we discussed the waveform of freely propagating Thz pulse and identify signals from reflected pulses. By dropping the reflected signal, Fourier transform spectrum had higher accuracy. To launch Thz wave into waveguide, one Teflon lens was used to focus Thz wave. A spot size of 0.7mm that approach the diffraction limit was achieved. By choosing low absorption and low dispersion material: Teflon, we demonstrated the efficacy of quasi-optical techniques to couple freely propagating pulses of THz radiation into Teflon waveguide. Even though our input spectrum overlaps the cutoff frequencies of more than 30 waveguide modes, the linearly polarized incoming THz pulses does not suffer seriouly modal dispersion by appropriately controlling the focus condition. This reveal that a large fraction of power of Thz wave was coupled into the fundamental mode.