Research On High-Repetition-Rate Mid-Infrared Optical Parametric Oscillator

The mid-infrared radiation source is of great importance to various civilian and military fields,such as air remote sensing,biomedicine,industrial manufacturing,and photoelectric countermeasure.Therefore,the demand for high repetition,high energy and narrow pulse width mid-infrared radition source is increasing.In this thesis,the threshold and conversion efficiency model of optical parametric oscillator(OPO)was studied theoretically.The thermal effect model of high-repetition-rate Nd:YAG laser was also theoretically studied,and the resonator was optimized.The mid-infrared pulsed laser with the low repetition and high-repetition-rate was studied experimentally.By optimizing the parameters such as the lengths of the nonlinear optical crystal and resonant cavity,a wide tuning and high energy mid-infrared laser was realized.The main work and innovations of this paper can be summarized as follows:1.The high energy,wide tuning low-repetition-rate mid-infrared OPO based on Ba Ga4Se7 crystal was realized.The linear and nonlinear infrared optical properties of Ba Ga4Se7 crystal were studied theoretically.Based on the theoretical model of doublepass single resonant optical parametric oscillator(DP-SRO),the effects of crystal length and resonant cavity length on the output characteristic were analyzed.The maximum pulse energy of 7.38 m J at 4.31μm was achieved,with the tuning range of3.70-4.84μm.The wide tuning range of 8.24-13.34μm was achieved,with a maximum pulse energy of 0.611 m J at 10.8μm.2.The high-repetition-rate pump laser of mid-infrared OPO,namely Nd:YAG laser,was studied.Based on the heat conduction theory,the temperature distribution on the cross section of the crystal rod in the Nd:YAG laser was simulated and analyzed,and the resonator structure was optimized.The LD side-pumped electro-optic Q-switched Nd:YAG laser was obtained experimentally.When the repetition rate was 1k Hz,the pulse energy of 1.064μm laser was 32.6m J with the pulse width of 20.0ns.3.The high-repetition-rate mid-infrared OPO based on Ba Ga4Se7 crystal was studied.The output characteristics of the DP-SRO based on Ba Ga4Se7 crystal pumped by a high-repetition-rate Nd:YAG laser was obtained experimentally for the first time.At a repetition rate of 100 Hz,the maximum pulse energy of 1.28 m J at the wavelength of 4.06μm was obtained with a pulse width of 13.6ns.At a repetition of1 k Hz,the maximum output energy of 20μJ/pulse at 4.06μm was obtained.