| A terahertz (THz) source with high quality is essential for THz studies and applications in biomedical diagnostcs, chemical identification, and space communication. The technique to generate terahertz radiation based on nonlinear difference-frequency mixing in nonlinear optical crystals enjoys the advantages of compactness, monochromatic output, no threshold, and operating at room temperature. The thesis analysed the factors to affect output of difference-frequency generation (DFG) according to the formula for calculating power output, and studied the DFG properties in detail for some important nonlinear optics crystals in terahertz radiation field.The main content of the thesis includes:(1) Factors to affect output power and conversion efficiency of DFG were analyzed. Methods to achieve phase-matching condition were summarized for different types of nonlinear crystals, and relative merits were analyzed for those phase-matching techniques.(2) The noncollinear phase-matching properties were studied for InP, CdTe, ZnTe crystals pumped by10,6μm laser and ZnSe crystal pumped by1.064μm and10.6μm laser. The collinear phase-matching angle, walk-off angle, allowed angle and effective nonlinear coefficient were calculated for CdSe crystal pumped by1.064μm and10.6μm laser. The relation between temperature changing and collinear properties was analyzed for InP, CdTe, ZnSe crystals. The collinear phase-matched curve of DAST organic crystal was alculated.(3) The collinear phase-matching properties of GaP crystal were studied detailedly, including curves of phase-matched wavelength, temperature characteristics, phase-matching bandwidth, output power and so on. The tuning plans were designed to generate terahertz radiation based on temperature changing pumped by1.064μm and1.030μm laser. A design was proposed to set up a portable THz source working at room temperature to generate terahertz wave at367μm and215μm. |
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