非稳腔Nd:YAG薄片激光器腔内离焦的影响和补偿

Influence and Compensation of Intra-Cavity Defocusing in Unstable Resonator Nd:YAG Thin-Disk Laser

基于腔内振荡激光波前曲率半径自再现条件，研究了腔内元件离焦对非稳腔腔内振荡激光参数的影响。在4片薄片串接的放大率为1.8的虚共焦非稳腔中，根据实验测量不同抽运功率下薄片的离焦量，当单个薄片具有焦距为-100 m 离焦时，激光-增益区交叠效率会降低9%，腔放大率升高至2.3，并因腔内激光尺寸与薄片有效孔径失配新增30%的腔内损耗，这些影响均会导致激光光光效率的降低。对比了几种离焦补偿方法，发现腔内插入变焦透射元件可以在大动态范围内实现较好的补偿效果。实验中，在腔内插入特别设计的光焦度可在- 0.016 m-1 到0.060 m-1调节的变焦透镜组，在4840 W 抽运条件下，离焦补偿后输出激光功率可以提升2.33倍，并且通过检测单程探测光束的波面特性，对激光器动态补偿，实现了1~100 Hz重复频率下单脉冲能量10 J激光输出。

Based on the self- reproduction condition of laser wavefront curvature, the influences of disk defocus on laser parameters are calculated. The overlapping efficiency decreases by 9%; the magnification rises to 2.3, and the intra-cavity loss increases to 30% due to a laser beam size mismatch when each disk has a focal length of -100 m in the positive-branch confocal unstable resonator containing four disk with magnification of 1.8. Therefore, the optical conversion efficiency and stability are reduced significantly. Several methods of defocus compensation are compared, it is found that inserting variable- focus lens in resonator is useful in large dynamic range. In the experiment, a lens group used for compensate components with the dynamic range from - 0.016 m- 1 to 0.060 m- 1 is designed carefully and inserted into the resonator. When the pump power is 4840 W , the output power can be improved by 2.33 times compared with that under the non- compensation condition. Under this compensation, the pulse energy of 10 J can be maintained from 1 Hz to 100 Hz.