为了提高倍频效率、分析倍频晶体内束腰位置对倍频效率的影响, 根据基模高斯光束传输特性, 结合稳定三镜折叠腔中端镜处等相位面曲率半径与腔镜曲率半径相等这一特点, 在激光光束传输的合适位置上, 放入与等相位面曲率半径相同的腔镜, 构成倍频晶体内具有两个瑞利长度的三镜折叠腔, 提高了倍频效率。对比了相同端镜构成的具有一个瑞利长度和两个瑞利长度谐振腔, 相对于分臂长度变化的稳区范围。结果表明, 使用5W光纤耦合880nm激光二极管, 端面抽运3mm×3mm×5mm的Nd∶YVO4, 采用10mm×2.1mm×0.5mm的PPMgOLN为倍频晶体, 使用具有两个瑞利长度的谐振腔比具有一个瑞利长度的谐振腔, 整体提高倍频效率约18%, 两种腔型的光束质量相同, 倍频光与基频光偏振方向一致, 输出稳定的低噪声绿光, 验证了谐振腔设计的有效性。该研究对腔内倍频效率的提高是有帮助的。

In order to improve the doubling frequency efficiency, the influence of beam waist position in frequency doubling crystal on the frequency doubling efficiency was analyzed. According to the propagation property of fundamental mode Gaussian beam, combining with the characteristic that equal phase plane of end mirror and cavity mirror having the same radius of curvature in the stable three-mirror-folded cavity, cavity mirror with the same radius of curvature was placed on the proper position and three-mirror-folded cavity with two Rayleigh length was realized. The efficiency of frequency doubling was improved. The stability regions of the cavity with one and two Rayleigh length were compared and the same stability regions were obtained. The experimental results show that when 5W fiber coupling 880nm laser diode is used to pump 3mm×3mm×5mm Nd∶YVO4 and quasi-phase matched PPMgOLN with dimension of 10mm×2.1mm×0.5mm is used as frequency doubling crystal, the overall conversion efficiency is improved about 18%. For the two types of cavity, beam quality is the same. The polarization direction of doubling frequency light is consistent with that of fundamental frequency light. Stable low noise green laser is obtained. The effectiveness of resonant cavity design is verified. The study is helpful to improve the efficiency of intracavity frequency doubling.