时空锁模超快光纤激光器研究

  超快脉冲光纤激光器因其所具备的小体积、高能量和易集成等优良特性在激光武器、激光医疗、激光通信等领域的被广泛应用，得到了研究人员的深入研究。但随着近些年，对更高能量激光脉冲和更大数据容量需求的不断增长，目前主流的单模光纤激光器已渐渐进入发展瓶颈阶段。使用多模光纤是克服这些限制最直接的方法，因为其具有更大的模场面积和额外的空间自由度。多模光纤的引入能够突破单模光纤激光器由于非线性效应带来的功率限制，进一步提升高功率光纤激光器的输出能力。在多模光纤中，多横模在空间域的叠加锁定为实现更高功率脉冲的输出带来了新的可能，时空锁模光纤激光器也被认为具备超越目前固体激光器性能的潜力

  本论文从理论和实验上对多模被动调Q与锁模两种光纤激光器进行了研究。首先探究了超短脉冲在多模光纤中的传输特性并对超短脉冲在渐变折射率光纤与阶跃折射率光纤中的传输进行了数值仿真，选择合适的光纤为后续搭建激光器进行铺垫；其次搭建了能够实现多模调Q的光纤激光器，该激光器实现了高能量的调Q脉冲输出，同时根据实验现象分析了非线性偏振旋转结构在多模调Q对于模式选择的重要作用；之后观察并记录了调Q与锁模两种状态在多模激光器中随泵浦功率变化而产生的相互转换；最后，通过分析时空锁模原理，设计并搭建了一种全多模光纤锁模激光器，通过优化实现了在皮秒量级脉宽的高能量脉冲输出，同时利用光束自清洁效应改善了光斑质量，构建了光束质量较好的高能量时空锁模光纤激光器。

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