High-repetition-rate nanosecond tunable mid-infrared(3~5μm) lasers have attracted the interest of scientists in many applications such as in military countermeasures and for environmental atmosphere monitoring, which has became an important research branch of laser technology. And the properties of high repetition rate, narrow pulse width master oscillator power amplifier(MOPA) 1064 nm laser pumped PPMg LN optical parametric oscillator(OPO) is an effective method to increase the repetition rate, to decrease the pulse width and to achieve high power output of mid-infrared laser, which has important guiding significance for the development of mid-infrared laser. In this thesis, based on the theory of QPM and OPO, we have analyzed the influence factors of increasing the conversion efficiency with high repetition rate, narrow pulse width mid-infrared laser, the structure design of 1064nm-MOPA pump laser and the PPMg LN-OPO device parameter optimization are developed as emphases.As the result, a high repetition rate narrow pulse width, wide tunable range mid-infrared laser is obtained. The primary research work and achievements of the paper is as follows:Theoretically, the coupled wave equations which covers the conversion of polarized state is deduced from the basic principles of QPM and optical parametric oscillator. The polarization coupling and reverse conversion effect which has influenced conversion efficiency of QPM-OPO is analyzed. Based on PPMg LN poled crystal, different tuning methods with PPMg LN-OPO is simulation studied.In aspect of numerical simulations studies, the pump structure for 1064 nm MOPA laser and PPMg LN-OPO are designed and optimaized. According to the rate equation of four-level system, the influence of different parameters on the repetition rate and pulse width of 1064 nm master oscillator is studied, a high density LD end-pumped coupling Nd:YVO4 device is optimally designed. By analyzing the thermal effect and simulating the thermal focal length of Nd:YVO4 crystal, and we also take into account the pattern matching between the pump light and resonance light spot, the structure parameter of 1064 nm master oscillator renonant cavity is optimized. Meanwhile, the 1064 nm modular ampilifier stage structure is designed from the basic principles of gain saturation effect and pattern matching. On this basis, we theoretical deduce and numerical simulate the gain, threshold, conversion effeciency and the thermal effect of PPMg LN crystal with single resonant external cavity pumped PPMg LN-OPO, the best value range of important parameters such as the curvature and transmittance of coupled cavity mirror, the ratio of pump light spot and parametric light spot, the type and size of resonant cavity are acquired.Experimentally, first we use the master oscillator power amplifier structure as the OPO pumping source, the master oscillator cavity is an L-shaped folded cavity, by placing the vertical slit in the cavity to limit the beam-spot mode, when the acousto-optic Q-switch repetition rate is 70 k Hz, the 40.1W maximum output power of 1064 nm is achieved with the secondary power amplifier, the pulse width is 9.82 ns. Then we use the above pumping strucure to study on the external cavity pumping OPO experiment. By using PPMg LN crystal with thickness of 3mm and poling period of 29μm as the frequency conversion medium, the 3.24 W maximum ouput power of 3.84μm laser and 9.01 W of 1.47μm are obtained. By analyzing the reverse conversion phenomenon in experiments, the maxmum output power of 4.86 W on 3.84μm laser is achived after changing the transmittance of OPO output mirror and adjusting the polarization state of pump light to optimize the pattern matching, corresponding to the pulse width is 9.56 ns and optical to optical conversion efficiency is 15.5%, the reverse conversion effect is effectively restrained. At last, we implement period tuning and temperature tunig experiment, by using the multi-periodic PPMg LN crystal with the grating period of 28.5~31.5μm and interval of 0.5μm, a tunable mid-infrared wavelength of 2965.5~4173.5nm is achieved, the tuning range is 1208 nm. Then we use the PPMg LN crystal with the single grating period of 29μm, by changing the temperature from 25 to 200℃, a tunable mid-infrared wavelength of 3765~3974nm is achieved,. |