为了增大皮秒注入种子激光的能量，获得较高的激光放大效率和信噪比，关键是要在保持较高的平均锁模激光功率下实现连续波锁模激光器的低重复频率运转。通过选取五镜折叠激光谐振腔腔型和参数设计，克服了随着腔长增加损耗加大而导致的激光锁模不稳定的困难。分析了较长腔长条件下工作物质和SESAM光斑尺寸的大小和变化，及其对激光器稳定性的影响。由于SESAM饱和工作和稳态条件的能量要求，在激光谐振腔调整过程中，对应臂长的光程互补变化。实验中采取腔长和晶体热控制方式，优化了激光谐振腔的工作参数，实现了脉冲能量10.7 nJ，重复频率56 MHz，平均功率1.2 W的SESAM连续波锁模激光输出。

To enlarge the energy of the pico-second laser pulse and to gain the higher laser amplifying efficiency and the higher ratio of the signal to noise in the pulse amplification, we should oscillate the CW mode-locked laser in the lower repetition frequency while the laser outputs the high average power. By designing and optimizing the five-mirror-folded laser resonator, we controlled the light loss increasing with the resonator length and the unstable running of the long cavity in CW laser mode-locked. We observed that the relevant or corresponding path of the resonator increase with the decrease of another arm path because of the energy requirements for the saturation working and stability state of the SESAM in the laser. We realized an SESAM CW mode-locked laser with the pulse energy of 10.7 nJ, the output power of 1.2 W.