Study Of Tunable THz-Wave Generation Via Difference Frequency Generation And Optical Parametric Process

The terahertz technique has attracted much attention from a variety of applications in fundamental and applied research field, such as physics, chemistry, life sciences, medical imaging, safety inspection, radio astronomy, modern communication, weapon guidance and so on. The technological progress of terahertz radiation source plays an important role in promoting the development of various terahertz technique and the related cross subjects. The generation of high-power, coherent, widely tunable, narrow-band terahertz wave, based on the process of the difference frequency generation and the stimulated polariton scattering in a polar crystal respectively, is expected to provide a promising terahertz radiation source with the obvious and exclusive advantages of compactness, simplicity for tuning, operation at room temperature and so on, which causes great research interest among the researchers all over the world. However, the research of this potential THz-wave generation technique is still in its infancy, and few relevant theoretical or experimental studies were reported in the domestic fields in recent years.The main contents and key creation points of this dissertation are as follows:1. A high-power, narrow-linewidth, angle-tuned pulsed dual-wavelength KTP-OPO operating near the degenerate point is experimentally demonstrated. The theoretical investigation of the phase-matching properties for the tunable coherent terahertz wave generation in the isotropic semiconductor nonlinear materials is presented, based on the dual-wavelength KTP-OPO mentioned above in the process of the difference frequency generation (DFG). The cross-Reststrahlen band dispersion compensation phase-matching technique involved in this interaction is introduced theoretically.2. According to the perfectly phase-matched wavelength range of the ZnTe crystal, we successfully showed a high-power, narrow linewidth, widely tunable, dual-wavelength KTP-OPO with two KTP crystals for the first time, which can be used as one of the most potential pump sources for the THz-wave DFG.3. The principle of operation of terahertz-wave parametric generation or oscillator (TPG / TPO) via the stimulated polariton scattering process is theoretically introduced in detail. The properties of THz-wave gain and absorption under different conditions in this process is presented. According to the investigation of the dispersion properties of the polariton in the polar crystal, a novel frequency tuning technique for TPO is reported for the first time. 4. According to the experimental results of TPG using LiNbO3, a high-power, coherent tunable Stokes light is obtained in the TPO experiments, which means that the tunable, coherent THz-wave radiation with high power is also generated. The phenomenon of the coherent tunable second-order Stokes light scattering is also observed.5. The phase-correcting Fresnel zone plate used in the terahertz region is designed, which provided an efficient lens-like focusing means of THz-wave radiation.