The Thz Generation And Detection Of The Radiation Pulse

Terahertz (THz) radiation occupies a large portion of the electromagnetic spectrum betweenthe infrared and microwave bands. In the last decade, rapid progress in ultrafast laser technologyprovides a steady and reliable optical source for the THz pulses generation, which greatlypromotes the research in the THz generation, detection and application. This thesis presents thetheoretical and experimental investigation of THz pulse generation and detection techniques and isorgniazed as follows.ChapterⅠintroduces the character of THz radiation. THz spectra of materials containabundant physical and chemical information. Therefore, THz technology has widely used in manydomains, for example foundational research. As THz technology is improving, new T raycapabilities will impact a range of interdisciplinary fields, including communications, imaging,medical diagnosis, health monitoring, environmental control, and chemical and biologicalidentification. It also offers an opportunity for transformational advances in defense and security.ChapterⅡpresents the two common ways to generation THz radiation pulse:photoconductive method and optical rectification method. We also introduced two ways to detectTHz radiation pulse: photoconductive sampling detection and electro-optic sampling detection.The woks point out that the physical essence of generation of generation of THz radiation pulse isa second polarization process. The theoretical basis is analyzed and described systematically.ChapterⅢanalyzes high-power narrow-band THz radiation emitted from a biasedlarge-aperture photoconductive antenna triggered by multiple-pulse trains. We have included theeffects of the finite lifetime and transient mobility dynamics of photogenerated carriers in theanalysis. THz waveforms are calculated from the saturation theory of large-aperturephotoconductors, and a comparison is made between single-pulse and multiple-pulse satruationproterties of THz emission from SI-GaAs and LT-GaAs emitters. The calculation show thesaturation at high fluence dendity with the interpulse spacing longer than the carrier lifetime can beavoided by mulitiple-pulse trains excitation large-aperture photoconductive emitters.ChapterⅣpresents our experimental investigation of THz generation by optical rectificationand detection by electro-optic sampling. We give the process of building a THz generation anddetection system, with emphasis on free space electro-optic sampling system. Primary experimental results of the THz measurement are presented.ChapterⅤgives a brief summary of this thesis and some suggestion for future experiments.