无源非稳腔内非共轭像差补偿研究

Research of Non-Conjugated Aberration Compensation in Passive Unstable Resonator

在具有腔内像差的虚共焦非稳腔内,因为振荡光束以不同光束尺寸通过腔内像差元件且像差元件对光束偏折,直接反向补偿和基于几何光学计算补偿后难以获得较好的补偿效果。提出了一种以导入腔内的准直光束作为参考,基于松弛迭代逼近补偿策略的腔内非共轭补偿方法,并计算验证了其可行性。从实验上对比了以单程和以往返测量光为参考的腔内补偿效果,发现以单程测量为参考的补偿不能使耦合输出光束质量明显提升。在往返补偿中,对4~6阶均方根误差为0.3~0.4μm的随机像差7~9次迭代可以实现收敛,补偿后往返探测光残差小于0.1μm,同时导引光在腔内多次振荡后从输出镜耦合输出的环形光束的β值由11.2降低至2.6。通过分析对比往返探测光束与腔内振荡激光的区别和关系,判断这种补偿方式可以对具有一定腔内像差的有源腔的振荡激光光束质量有效提升。

The effects of intracavity aberration compensation based on negation of phase or calculation of geometrical optics in positive-branch confocal unstable resonator is not ideal because of the different sizes of oscillation laser （plane wave and spherical wave） on optical elements and light deflection caused by the aberration. A non-conjugated intra-cavity aberration compensation method based on the relaxation iterative approximation algorithm using a collimated probe beam wavefront as the reference is presented. In experiment, the effects of compensation referenced single pass probe and round-trip probe are compared. It can be found that the beam quality of output guided light cannot be improved in the compensation using single pass probe. The round-trip probe wavefront can begin to stabilize and the root mean square （RMS） of residual error is less than 0.1 pm after 7-9 iterative steps, when the value of RMS of the random intra-cavity aberration is 0.3-0.4 μm. The β value of output guided light, which is as the evaluation criterion, can be decreased from 11.2 to 2.6 with the compensation. By analyzing of the relationship and difference between the guided light and the oscillation laser, it can be inferred that the beam quality of output laser in an active unstable resonator will be improved using this aberration compensation method.