Ultrafast Imaging of Terahertz Pulses

The main purpose of this thesis is to develop terahertz (THz) generation, detection, and spectroscopy techniques via ultrafast imaging methods.;Sampling THz pulse waveforms with anoncollinear imaging technique was carried out. Full-field images of the THz electric field waveforms sampled in E-mode can be used to performTHz spectroscopy, but multi-shots are required. On the other hand, the square of the THz electric field waveforms is obtained in a single shot in E2-mode, which enables single-shot THz spectroscopy of the transmitted THz power spectra.;In order to study the THz generation process by optical rectification in LiNbO3 crystals, we developed a novel transverse imaging technique to image the THz Cherenkov wave in side-view mode and top-view mode. Based on the images of the THz Cherenkov wave generated by the point focused optical pump pulse, parameters including the Cherenkov angleand group and phase velocities of the optical pump pulse and THz pulse, respectively,aremeasured directly. A transition-like radiation generated at the crystal boundary is imaged for the first time. Imaging distortionsdue to the transverse imaging geometry aresimulated and a correction chart is made.;We also imaged THz pulses generated with the titled-pulse-front excitation technique in real time. The real time visualization ofTHz pulse generation and propagation in LiNbO3 crystals enables us to optimize the THz pulse generation efficiency in a more directway. Based on the transverse imaging technique, THz pulse reflection, transmission, and tunneling in various conditions are imaged, which may be useful in physics teaching demonstrations. Applications of the transverse imaging technique to image THz generation inperiodically poled lithium niobate (PPLN), air plasmasgenerated by femtosecond laser pulses, and nonlinear optical Kerr effect signals induced by femtosecond laser pulses in CS2, quartz,water, methanol, and THFare explored.;Finally, a new type of free-standing, frameless carbon nanotube array THz polarizer is fabricated and tested.