复合型狄拉克材料的制备及其在超快激光中的应用研究

Development of ultrafast laser is largely dependent on the development of saturable absorption material. Graphene and topological insulators are typically Dirac materials. Currently research, including research conducted by our group in recent years, have proved that graphene or topological insulators as saturable absorber has lots of advantages, such as high thermal damage threshold, great modulation depth, wide wavelength tuning range, and short recovery time. It is conducive to the realization of a high-power and long stable mode-locked operation. But there is also a lot of problems, such as large lattice mismatch, easily oxidized, small size, layers uncontrollable, easily damaged during transfer process. Based on our research, composite Dirac saturated absorber is made with topological insulators growing on graphene substate, which can overcome drawbacks of topological insulators or graphene alone as saturable absorber and further improve optical absorption proproties. By exploring the growth mechanism, the optimized growth condition can be found, by improving the material transfer techniques, the material's layer, thickness and area can be precisely controlled, and then the optimization of the parameters of the composite saturable absorber can be got. Dirac material is directly grown on a quartz fiber, avoiding damage caused by the transfer process, and increase the saturation absorption properties of Dirac materials. After optimizing the parameters of the solid-state and fiber laser, a femtosecond 1-3 μm continuous mode-locked laser stable output can be obtained.

超快激光的发展在很大程度上依赖于可饱和吸收材料的发展。目前已有的研究包括本课题组近几年开展的研究表明以石墨烯和拓扑绝缘体为代表的狄拉克材料作为饱和吸收体具有损伤阈值高、调制深度大、波长可调谐范围宽和恢复时间短等优点，有利于实现高功率长时间稳定的锁模运转，同时也存在晶格失配大、容易氧化、尺寸小、层数不可控以及转移过程易造成损伤等问题。本课题在过去研究的基础上，将在石墨烯基底上生长拓扑绝缘体形成复合型狄拉克饱和吸收体，以克服二者单独作为饱和吸收体所存在的不足，进而改善光学吸收特性；通过对生长机理的研究，寻找最佳生长条件，通过改进转移技术精确控制材料的层数、厚度和面积，实现对复合型饱和吸收体参数的优化；探索在光纤上直接生长狄拉克材料，避免转移损伤，提高狄拉克材料的饱和吸收性能；将复合型饱和吸收体分别应用于固态激光器和光纤激光器，通过优化参数，最终实现飞秒量级1-3μm波段连续锁模激光的稳定输出。

可饱和吸收体对于获得超快激光具有至关重要的作用。项目采用CVD方法，分别制备了石墨烯、拓扑绝缘体以及复合型狄拉克材料，并研究了生长条件对材料性能的影响。制备了石墨烯和石墨烯/Bi2Se3/石墨烯的三明治饱和吸收体，分析了饱和吸收体的光损伤阈值、调制深度、非线性可饱和吸收系数及线性透过率等饱和吸收参数。分析了基于Bi2Se3 可饱和器件的新型掺Nd光纤激光1360.61nm波段的被动调Q锁模输出特性。并成功将CVD法制备的石墨烯/Bi2Se3/石墨烯“三明治“结构分别转移到光纤端面，在1.5微米实现输出功率150 mW的锁模激光输出，脉冲宽度为2.3 ns、重复频率3.2 MHz。该实验结果相对于传统材料锁模的mW级别输出功率有了极其明显的提升。通过开孔Z扫描技术，研究了石墨烯/金纳米棒复合结构的非线性光学响应。为了更好与目前锁模领域其他可饱和吸收材料进行对比，利用热分解的方法，在云母表面分别制备了二硫化钼和二硫化钨，研究了二极管泵浦Nd:GdVO4激光器中插入MoS2可饱和吸收体和掺饵光纤激光器中插入WS2可饱和吸收体时锁模输出特性，分析了不同饱和吸收体材料对调制深度、最大重复频率、最大输出功率等参数的影响。为在本项目的资助下，还开展了石墨烯、过渡金属硫化物与金属纳米结构复合材料的制备，并应用到表面增强拉曼光谱领域。