Cui Xing-Yang, Shen Qi, Yan Mei-Chen, Zeng Chao, Yuan Tao, Zhang Wen-Zhuo, Yao Xing-Can, Peng Cheng-Zhi, Jiang Xiao, Chen Yu-Ao, Pan Jian-Wei
Opt Lett. 2018 Apr 15;43(8):1666-1669. doi: 10.1364/OL.43.001666.
Second-harmonic generation (SHG) is useful for obtaining single-frequency continuous-wave laser sources at various wavelengths for applications ranging from biology to fundamental physics. Using an external power-enhancement cavity is an effective approach to improve the frequency conversion efficiency. However, thermal effects limit the efficiency, particularly, in high-power operation. Therefore, reducing thermal effects is important when designing a cavity. This Letter reports the use of an external ring cavity for SHG, yielding a 5.2 W, 671 nm laser light with a conversion efficiency of 93.8±0.8% which, to the best of our knowledge, is a new record of conversion efficiency for an external ring cavity. It is achieved using a 10 mm length periodically poled potassium titanyl phosphate crystal and a 65 μm radius beam waist in the cavity so as to minimize thermal dephasing and thermal lensing. Furthermore, a method is developed to determine a conversion efficiency more accurately based on measuring the pump depletion using a photodiode detector and a maximum pump depletion up to 97% is recorded. In this method, the uncertainty is much less than that achieved in a common method by direct measuring with a power meter.
二次谐波产生（SHG）对于获得各种波长的单频连续波激光源很有用，其应用范围涵盖从生物学到基础物理学等多个领域。使用外部功率增强腔是提高频率转换效率的有效方法。然而，热效应会限制效率，特别是在高功率运行时。因此，在设计腔时减少热效应很重要。本文报道了将外部环形腔用于二次谐波产生的情况，产生了功率为5.2瓦、波长为671纳米的激光，转换效率为93.8±0.8%，据我们所知，这是外部环形腔转换效率的新纪录。这是通过在腔内使用长度为10毫米的周期性极化磷酸钛氧钾晶体和半径为65微米的束腰来实现的，以便将热退相和热透镜效应降至最低。此外，还开发了一种基于使用光电二极管探测器测量泵浦耗尽来更准确确定转换效率的方法，并记录到最大泵浦耗尽高达97%。在这种方法中，不确定性远小于通过功率计直接测量的常规方法所达到的不确定性。
