理论上分析了掺MgO的周期极化LiNbO3(PPMgLN)晶体准相位匹配光参量振荡(QPM-OPO)波长的调谐特性,计算了抽运阈值和转换效率。采用高斯光束抽运,当抽运功率密度为阈值抽运功率密度约6.5倍时,可以获得约71%的转换效率。而相位匹配情况下,平面波抽运功率密度为阈值(π/2)2倍时,转换效率可达到100%。1064 nm激光抽运PPMgLN晶体(MgO摩尔分数5%),单谐振光参量振荡技术采用e→e+e相位匹配,利用PPMgLN晶体的最大非线性系数d33(27.4 pm/V),采用周期调谐方式,实验上获得了中红外波长调谐范围2.7～4.8 μm,当抽运功率为23 W,频率为7 kHz时,在波长3.7 μm处激光输出功率超过3.2 W,斜率效率超过18%,对应闲频光波长1.49 μm输出功率约8 W,相当于转换斜率效率约为63%。实验结果与理论分析基本一致。

Theoretical and experimental study is presented on grating period-tuned single-resonated quasi-phase-matched optical parametric oscillator (QPM-OPO) in multi-grating periodically poled lithium niobate (PPMgLN) pumped by 1064 nm laser. Theoretical analysis includes grating period tuning, pump threshold and converting efficiency. When pump power is 6.5 times of the pump threshold with Gauss beam pumping, a converting efficiency of 71% is obtained, however a converting efficiency of 100% may be obtained when pump power is (π/2)2 times of the pump threshold with plane wave pumping and phase matching. The pump beam polarization matches the e→e+e interaction in PPMgLN, thus maximal nonlinear coefficient d33 (27.4 pm/V) is effective. Widely mid-infrared wavelength tunable output from 2.7 μm to 4.8 μm has been obtained by grating period tuning. When pump power is 23 W with repetition rate of 7 kHz, an average output power of more than 3.2 W at 3.7 μm is obtained with slope efficiency of more than 18%, and 8 W at the corresponding idler wavelength of 1.49 μm and a corresponding converting efficiency of 63% are obtained. The experimental data are in agreement with numerical analysis results.