多场耦合作用下浸入式液冷激光器自适应谐振腔调控基础问题研究

The immersed liquid-cooled laser is a promising architecture of the next generation solid-state lasers for its advanced heat management and power scaling potential. However, the beam quality is severely limited by multi-physics coupling inside the resonator. We propose fundamental studies of adaptive resonator manipulations for immersed liquid-cooled lasers under multi-physics coupling through theoretical analyses, numerical simulations and experimental researches. We will establish a multi-physics model of the gain chamber, through which the mechanism of aberration generations and fundamental requirements of resonator manipulations would be determined. We will build a physics model of the entire immersed liquid-cooled laser including the intracavity adaptive optics system, through which the strong coupling of intracavity aberrations and field distributions of the output beam could be studied. We will investigate the mechanism and realization of adaptive resonator manipulations, and the highest attainable beam quality and its constraints will be clarified. We will achieve beam quality of better than 2 times of diffraction limit with a kW-level Nd:YAG immersed liquid-cooled laser based on adaptive resonator manipulation. This project will derive the architecture of adaptive resonator manipulations for immersed liquid-cooled lasers, which will promote the ongoing developments of high average power and high beam quality immersed liquid-cooled lasers.

浸入式液冷激光器具有先进的热管理方式和优异的定标放大能力，是近年来兴起的新一代高平均功率固态激光器。谐振腔内多物理场耦合过程是限制这类激光器光束质量的主要瓶颈。本项目拟采用理论分析、数值模拟和实验研究相结合的方法，深入研究多场作用下浸入式液冷激光器自适应谐振腔调控基础问题。本项目将建立增益池多物理场耦合模型，明确像差产生机理及其对谐振腔调控的基本要求；构建包含腔内自适应光学在内的浸入式液冷激光器全系统物理模型，明晰光场分布与腔内像差之间的强耦合机制；开展自适应谐振腔调控机理与实现方法研究，阐明光束质量的物理限制和改善光束质量的极限能力。在解决上述问题的基础上，基于千瓦级Nd:YAG浸入式液冷激光器开展自适应谐振腔调控实验研究，预期光束质量优于2倍衍射极限。本项目将建立浸入式液冷激光器自适应谐振腔调控的理论与实验体系，对于我国正在开展的该类高功率激光器研究具有重要的理论意义与应用价值。

高能固体激光中，当功率未达到一定功率时，采用自适光学系统进行常规腔外波前探测及实时校正就能实现较好的光束质量，此外十一五、十二五期间，国家在化学激光和固体激光净化方向均有较多投入，自适应光学激光光束净化在关键器件研制和关键技术有了长足进展。国内高能固体激光在功率方面较国外有较大差距，十三五期间，固体激光采用与之前不同技术路线，功率相比以前提升5-10倍，激光器工作过程中，腔内元件热畸变、泵浦和增益主动冷却系统使得谐振腔的影响以不可忽略，它不仅使得激光功率下降，输出激光模场不稳定，采用传统腔外自适应光学系统难以达到满意的校正目标。如今，高能固体激光功率不断逼近应用门槛，腔内光束抖动和腔内畸变成为其激光功率和光束质量的主要影响因素，为实现“三高”固体激光，谐振腔内光束主动校正成为其难以回避的关键问题。本课题针对该问题开展了三方面的研究工作：首先建立了基于Fox-Li数值迭代法的谐振腔内自适应校正数值模型，定量分析了腔内像差校正前后对输出光束的光场分布的影响；其次在总结已有非稳腔内校正技术的基础上，提出了环形非稳腔内像差共轭校正的技术路线，搭建了千瓦级固体激光系统，开展了环形腔倒向波抑制的理论与实践工作，实现了超过1kW功率输出；最后，开展了腔内自适应光学系统设计，并集成于千瓦级环形非稳腔固体激光器，通过腔内倾斜与像差校正将千瓦级固体激光输出光束质量提升3倍衍射极限以内。课题通过针对固体激光非稳腔调控问题开展了深入系统地理论和实践研究，提出了基于环形非稳内自适应校正的高功率固体激光方案，并通过实验验证该方案能实现高功率和高光束质量，为高能固体激光实现“三高”开辟新的技术路线。