THz Pulse Generation And Detection

Terahertz (THz) radiation, which occupies a large portion of the electromagnetic spectrum between the infrared and microwave bands. In the last decade, rapid progress in ultrafast laser technology provides a steady and reliable optical source for the terahertz (THz) pulses generation, which greatly promotes the research in the THz generation, detection and application that is difficult to access before. The thesis is organized as follows:Chapter one presents an introduction to the general characteristics of THz radiation. THz spectra contain abundant physical and chemical information of materials. Therefore, THz technology has widely used in many domains, for example fundamental research. As THz technology is improving, new T ray capabilities will impact a range of interdisciplinary fields, including communications, imaging, medical diagnosis, health monitoring, environmental control, and chemical and biological identification.Chapter two describes two ways to generate THz radiation pulse: photoconductive antennas and optical rectification. The physical essence of generation of THz radiation pulse is a second polarization process is emphasized. We also give an introduction of the two ways to detect THz radiation pulse: photoconductive sampling and free space electro-optic sampling. The theoretical basis is analyzed and described systematically.Chapter three discusses the surface and far field temporal characteristics of terahertz radiation generated by biased large-aperture photoconductive antennas with finite thickness. Not only the effects of the finite lifetime and transient mobility, but also the effects of optical time lag and absorption attenuation in photoconductor material, are included in the presented model. The dependence of the waveforms of the radiated field on optical fluence, optical widths, carrier relaxation time, carrier lifetime and material thickness are discussed in detail. A comparison of the terahertz temporal profiles is made between ideal antennas without thickness and practical antennas with finite thickness.Chapter four presents our experimental study of THz generation by optical rectification and detection by electro-optic sampling. We build an experimental setup in-house. We describe in detail the processes of the building the THz generation and detection system, especially free space electro-optic sampling system. Experimental results are presented and analyzed.Chapter five is the summary of this thesis.