Study On Optical Difference-frequency Generation Of Mid-infrared Laser And Terahertz Radiation

Due to the special position of terahertz frequency between electron and photon frequency, it displays great potential applications in those areas such as special analysis, medial imaging, environmental monitoring, communication and national defense and can find favor in researchers'eyes. Mid-infrared laser source is of great interest for paramount applications from remote sensing and special analysis to industrial process control, photobiology, photochemistry, military and so on. Tunable and coherent sources are of great emphasis in those areas. Difference-frequency generation of terahertz and Mid-infrared radiation based on the nonlinear optical frequency conversion technology has numerous advantages, such as operating at room temperature, widely tunable ranges, high peak power and compactness. The main content and creative points in the dissertation as follows:1. The important features of terahertz radiation and its applications are viewed. Terahertz radiation generated by optical method has been introduced. A detailed summary of terahertz source development is made around home and abroad. Development and generation methods of Mid-infrared radiation are also introduced around home and abroad.2. According to the coupled-wave equation, energy transfer among the three waves has been researched in approximate model of plane wave and Gauss wave. The difference of restrictive conditions in both models is discussed.3. An analysis is taken for nonlinear DFG crystals about their characteristic, phase matching condition and relation of dispersion in the range of Mid- infrared radiation. Using a 1064nm semiconductor laser with repetition frequency of 10Hz as a pumped source to pump KTP optical parametric oscillation, dual-wavelength degenerated point around 2.1μm is obtained. Tunable Mid-infrared radiation is achieved based on dual-wavelength nonlinear DFG in GaSe crystal. Mid-infrared radiation in the range of 7-19μm is obtained with peck power of 7.5kW.4. Based on the internal pumped KTP optical parametric oscillation with dual- wavelength around 2.1μm, tunable mid-infrared radiation in the range of 7-12μm is obtained by DFG in ZnGeP2 crystal. Peck power of output energy is achieved 2.23kW.5. Using dual KTP optical parametric oscillator as pump source, experimental simulation of DFG based on ZnGeP2 crystal is designed. Time and frequency spectrum of terahertz pulse is achieved in the periodic poled crystal based on DFG with ps pulse as the pump pulse. Factors that effect walk off length are explained. According to the normalized coupled-wave equation, factors that...