高功率光纤激光反常受激拉曼散射机理研究

High power fiber lasers have attracted a lot of attentions due to its widely potential applications in many fields, such as industrial processing, scientific research and national defense. Because it is a complex coupling system with multi-physical process, high power fiber lasers exhibit many brand new physical phenomena, one of which is the abnormal forward stimulated Raman scattering (SRS) observed in several independent experiments very recently. It shows that the SRS power threshold is much lower than the theoretical prediction and the anti-Stokes wave can be observed under some conditions. On the other hand, SRS is an important factor which limits the power scalability of high power fiber lasers. In this research project, we focus on the SRS process within high power fiber laser, especially the abnormal forward SRS phenomenon. The physical mechanism will be studied systematically with the combination of theory and experiment. New ideas of SRS suppression in high power fiber lasers will be proposed and its application in Raman fiber laser will be explored as well.

高功率光纤激光在包括工业加工、基础科研、国防反恐等众多领域都得到了广泛应用，近年来发展迅猛。由于高功率光纤激光器是一个多物理过程的复杂耦合系统，不断涌现中各种新的物理现象，最近我们在一系列无相关性的实验中观察到的反常前向受激拉曼散射（SRS）就是其中之一。它表现为在远低于理论预期的功率水平下即观测到SRS，同时可能伴随着反Stokes光的出现。另一方面，SRS也是制约高功率光纤激光功率进一步提升的核心因素。本课题拟以高功率光纤激光中的受激拉曼散射为研究对象，系统深入研究其中的影响因素，特别针对反常前向SRS现象，采用理论与实验相结合的方式，揭示该现象的物理机理。基于此提出高功率光纤激光中SRS抑制的新思路，并探索它在拉曼光纤激光器中的应用。

采用理论与实验相结合的方式，研究高功率光纤激光中的SRS效应。结果表明，高平均功率光纤激光器中的强前向SRS主要起源于种子源强烈的时域抖动特性。整个过程可以用推广的非线性薛定谔方程较好的模拟。一些减小种子源时域起伏的方法能够抑制SRS。如使用DFB+白噪声调制、使用随机激光种子源、通过插入适当长度的无源光纤。这些方案对抑制SRS，进一步提升光纤激光功率有重要参考价值。