为了优化MgO∶PPLN连续光参量振荡器(OPO)的输出特性, 对三镜直腔结构的内腔式OPO系统进行腔结构设计, 对其同时输出高效的信号光和闲频光进行研究。采用半导体激光端面抽运Nd∶YVO4晶体实现连续的1 064 nm激光为基频光。对比分析了基频激光腔和OPO腔各腔镜分别采用平面镜或平凹镜的三种腔型结构的激光输出特性。基于30.5 μm的极化周期和12.4 W入射抽运功率时, 获得了最高输出功率3.92 W(信号光2.6 W和闲频光1.32 W), 转化效率31.6%的激光输出, 对应的信号光和闲频光的中心波长分别为1 549 nm和3 394 nm。结果表明三个腔镜均采用平凹镜时, 可有效的压缩基频激光腔在MgO∶PPLN晶体上的光斑, 提升基频激光的功率密度, 而且基频激光腔和OPO腔的基模光斑在MgO∶PPLN晶体上更好的匹配, 从而提升变频效率。

In order to optimize the output characteristics of continuous-wave singly resonant MgO∶PPLN optical parametric oscillations (OPO), a compact three-mirror linear cavity structure was designed for efficient signal light and idler light outputs. A diode laser end-pumped Nd∶YVO4 crystal laser at 1 064 nm was used as the fundamental laser source to derive the OPO in the cavity. Three laser cavities with cavity mirrors chosen from plane mirror or plano-concave mirror were designed for comparison. The simulation results show that the fundamental laser beam could be compressed, and the power density could be improved on the MgO∶PPLN crystal if all three cavity mirrors used the plano-concave mirror (named concave-concave-concave cavity in this paper). The frequency conversion efficiency would be improved for better mode matching between the fundamental cavity and the OPO cavity with the concave-concave-concave cavity. A total output power of 3.92 W and conversion efficiency of 31.6% were obtained at the incident pump power of 12.4 W and grating period of 30.5 μm. A 2.6 W light signal with the center wavelength at 1 549 nm and 1.32 W idler light with center wavelength at 3 394 nm were achieved.