新型二维过渡金属硫化物/石墨烯异质结可饱和吸收特性及其在超快光纤激光器中的应用研究

Saturable absorber is the key material for obtaining picosecond and femtosecond ultrafast lasers through mode-locked technology. Currently, the most used semiconducting saturable absorber mirrors have problems such as complex preparation methods, high cost and narrow working wavelength range (<100 nm). Therefore, it is necessary to explore novel saturable absorption materials with advantages such as simple preparation method, low cost and broad working wavelengh range. The novel two-dimensional transition metal dichalcogenides,typically as WS2 and MoS2, have been potential candidates owing to their small energy bandgap, broad working wavelength range and large modulation depth, however, it has poor pulse width compressibility because of its long exciton recovering time. In this project, two-dimensional transition metal dichalcogenides /graphene heterostructure are fabricated through magnetron sputtering method and used as saturable absorber, combining the advantages short exciton recovering time of grahene and high modulation depth of transition metal dichalcogenides, in order to obtain novel saturable absorbers which have high modulation depth and capability of compressing pulse width into several picoseconds, even more femotosecond level. The novel heterostructure saturable absorber will finally be used in a near-infrared mode-locked fiber laser system to form picosecond and femtosecond ultrafast fiber laser with stable output, promoting development of the novel mode-locked lasers.

可饱和吸收体是锁模技术获得皮秒及飞秒超快激光的关键材料，目前应用较多的半导体可饱和吸收镜存在制备工艺复杂、成本高、工作波长范围窄（<100 nm）等问题，因此亟需开发工艺简单、成本低、工作波长范围宽的新型高性能可饱和吸收体材料。以WS2、MoS2为代表的新型二维过渡金属硫化物由于具有带隙小、工作波长范围宽、调制深度大等特性而成为一种极有潜力的可饱和吸收体材料，然而，其激子恢复时间长导致脉宽压缩能力弱，较难得到超短脉冲激光。本项目拟采用磁控溅射法设计制备二维过渡金属硫化物/石墨烯异质结作为可饱和吸收体，通过结合石墨烯激子恢复时间短和过渡金属硫化物可调制深度大的优势，获得调制深度大且能有效压缩激光脉冲至几个皮秒、甚至飞秒量级的高性能可饱和吸收体。并进一步将其应用于近红外锁模光纤激光系统，研制基于该新型异质结可饱和吸收体的具有稳定输出的皮秒及飞秒超快光纤激光系统，推动新型锁模激光器的发展。

皮秒以及飞秒激光由于其脉宽窄、峰值功率高的特点，在基础科研、精密测量、超精细加工以及国防领域都具有极其重要的作用。可饱和吸收材料是通过被动锁模产生稳定超快激光的核心部件，目前所使用的SESAM存在工作波长单一、损伤阈值低、制备方法复杂、成本高以及国外技术垄断等问题，寻求可替代SESAM的新型可饱和吸收材料的研究工作具有重大意义。针对这一亟待解决的问题，依托本项目，制备了一系列新型二维材料和异质结，并研究其可饱和吸收性质及其在锁模激光中的应用。采用磁控溅射法制备了大面积均匀的WS2, PtSe2, SnS2等薄膜，对这些材料的非线性吸收性质研究结果表明其对于超快激光均具有明显的可饱和吸收性质，另外，采用了不同脉宽(ns, ps, fs)的激光对WS2薄膜的非线性吸收性质进行了测试，结果表明WS2对于脉宽远大于其激发态载流子寿命的脉冲激光不表现出可饱和吸收性质，这一发现对材料的非线性吸收性质的研究具有指导意义。在掌握了一系列二维材料制备方法的基础上，实现了基于WS2, PtSe2, TaS2, ReSe2, GeS等新型二维材料的锁模激光输出，在1 μm光路中，实现的最窄脉冲输出为573.5 ps，1.5 μm光路中为854 fs，这些成果表明二维过渡金属硫化物具有潜力成为新一代可饱和吸收材料。对项目成果进行总结，共发表了SCI论文15篇，其中一作/通讯论文12篇，申请中国发明专利5项。