拓扑绝缘体的宽带非线性可饱和吸收特性及在超快激光的应用研究

Saturable absorber is one of the key elements of the passively mode-locked laser. SESAM, as the most common mode locker, has the disadvantages of complex fabrication and narrow absorption range, limiting the development of the ultrafast laser. Therefore, it is crucial to look for new saturable absorber with high performance and low cost. Three-dimensional topological insulators are a new state of quantum matter with gapless edge or surface states, topologically proprotected against all time-reversal invariant perturbations. Three-dimensional topological insulators exhibit various advantages such as wideband nonlinear saturable absorption and ultrafast relaxation duration, similar to graphene. Moreover, the modulation depth is obviously higher than that of graphene and SESAM, benefiting for generating ultrashort pulses and suppressing pulse breaking. We will research the photoelectrical properties of the new-typed Three-dimensional topological insulators, Bi2Se3 family (Bi2Se3, Bi2Te3,and Sb2Te3). The intrinsic relation between the characteristics of the topological insulators and the time- frequency properties of ultrafast pulses will be studied. Novel wideband saturable absorption mirrors will be fabricated. With Nd3+,Yb3+,or Tm3+ doped laser crystals, the efficiently high-power all-solid-state mode-locked lasers at 1.0-2.0 μm will be realized with the three-dimensional topological insulators as saturable absorbers. This subject is focusing on the basic research and application of the topological insulators, in order to achieve high-performance and low-cost ultrafast lasers to satisfy the urgent need of industry and national defense.

可饱和吸收体是被动锁模激光的核心部件之一。常用的可饱和吸收元件SESAM制备复杂、吸收带宽窄，极大限制了超快激光的发展，因此急切需要新型可饱和吸收材料。三维拓扑绝缘体是一种新奇的量子物态，具有时间反演对称的无能隙表面态，表现出与石墨烯类似的宽带非线性可饱和吸收、超快弛豫时间等优点。而且调制深度大大高于石墨烯和SESAM，利于产生超短脉冲以及避免高脉冲能量导致的脉冲分裂现象。本课题对Bi2Se3家族（Bi2Se3、Bi2Te3和Sb2Te3）这一类新型三维拓扑绝缘体的光电性能进行研究。明确各宏观参量与锁模脉冲时域频域性质的内在关系；制备具有应用价值的宽带可饱和吸收镜；基于掺Nd、Yb、及Tm激光晶体，实现拓扑绝缘体锁模的1.0-2.0μm高功率、高效率全固态超快锁模激光。本课题旨在开展拓扑绝缘体这一新型优秀材料的基础研究和应用开发，为有效提高超快锁模激光性能、降低成本奠定理论和技术基础。

本项目旨在探索新型三维拓扑绝缘体等具有二维层状结构的光电材料在1-3μm全固态超快锁模及调Q激光的应用，在执行期间，遵循既定的研究方案和计划，较好的完成了本项目的研究目标。主要研究成果如下：.(1)优化了二维层状材料的制备方法，用液相剥离法、水热法、溶剂热法实现拓扑绝缘体Bi2Te3、Bi2Se3，过渡金属硫化物MoS2、WS2，黑磷，以及Bi2Te3-石墨烯异质结等二维材料的高质量、高产率、纳米到微米尺寸的薄片制备。系统表征了微观形貌、物理光学、非线性光吸收特性。研究了拓扑绝缘体独特的能带结构体态和表态的复合效应导致高灵敏可饱和吸收的物理机理。.(2)实现了Bi2Te3调制的1.06μm和1.34μm低阈值Nd3+:YVO4调Q激光器，1064nm调Q激光阈值仅为32mW，是已知固体调Q激光的最低值。同时也实现了Bi2Te3调制的1.06μm和1.34μm调Q锁模激光，平均输出功率分别为38.3mW和37mW，锁模脉冲重复频率为~5GHz。.(3)实现了Bi2Te3调制的1μmYb:KGW飞秒锁模激光器，脉冲宽度为693fs，平均输出功率为89mW，脉冲重复频率为89MHz。.(4)实现了Bi2Te3调制的2μm波段Tm:YAP锁模激光，平均功率为260mW，锁模脉冲重复频率为75MHz，脉宽经计算约为750ps。证明了拓扑绝缘体在中红外波段也就具有较好的光学性能。.(5)实现了Bi2Te3调制的2.8μmEr:YSGG调Q激光器，稳定输出功率为106mW，脉冲重复频率为51.6kHz，脉冲宽度为476ns，脉冲能量为2.1μJ。实现了WS2调制的1.0μm波段Yb:GAB调Q激光器以及黑磷稳频的1.0μm波段双波长Yb:GAB调Q激光器。.本工作实现了二维材料调制的1-3µm波段多种纳秒、皮秒、飞秒调Q和锁模激光，有望满足集成光学系统对微型化、集成化、低功耗的激光光源的需求。