Kedmi J, Treves D
Appl Opt. 1981 Jun 15;20(12):2108-12. doi: 10.1364/AO.20.002108.
The problem of transverse-mode matching between the lowest-loss mode of a confocal unstable resonator and a Gaussian beam, which is injected into the resonator through a coupling hole in its back mirror, is analyzed. It is found that in resonators having equivalent Fresnel number >0.5, there is a value of the coupling hole diameter for which a mode transition occurs. Below this value the coupling coefficient between the mode and the injected signal increases with the hole diameter. The optimal coupling hole diameter for injection locking lies somewhat below the transition value, where the low-order mode is still dominant and the coupling coefficient is high (0.25-0.30). The power loss through the coupling hole is negligible (2%) compared to the output coupling, which is ~50-70%.
分析了共焦非稳腔最低损耗模式与通过后镜耦合孔注入腔内的高斯光束之间的横模匹配问题。研究发现，在菲涅尔数大于0.5的谐振腔中，存在一个耦合孔直径值，在此直径下会发生模式转换。低于此值时，该模式与注入信号之间的耦合系数随孔径增大而增大。注入锁定的最佳耦合孔直径略低于转换值，此时低阶模式仍占主导，且耦合系数较高（约0.25 - 0.30）。与约50 - 70%的输出耦合相比，通过耦合孔的功率损耗可忽略不计（约2%）。
