Liang Shuang, Lu Yuze, Liu Haimu, Shang Xiaohe, Du Rongguang, Ji Jiamin, Yu Yiling, Zhang Shunping
Opt Express. 2025 Feb 24;33(4):7266-7277. doi: 10.1364/OE.539834.
Layered materials such as graphene and transition metal dichalcogenides (TMDs) are excellent candidates as saturable absorbers. However, the saturable absorption of few-layer TMDs is usually measured at the typical wavelengths of lasers, away from the exciton resonances. In this work, we study the saturable absorption effects in one, two, and three-layer WS and WSe, around the A-exciton resonance, using a tunable pulsed laser. Power-dependent reflectance contrast indicates that the saturation power density thresholds are around 5.5 × 10 W/cm (3.8 × 10 W/cm) for monolayer WS (WSe), showing an order of magnitude reduction at the exciton peak. The saturation power density threshold increases with the number of layers. The analytical solution to the dynamics equation illustrates how the laser parameters influence the experimentally measured threshold, highlighting the importance of pulse duration in saturable absorption. This result reveals the effect of exciton decay and exciton-exciton interactions on the nonlinear optical properties of TMDs and benefits the design of TMD-based active optical devices.
诸如石墨烯和过渡金属二硫属化物（TMDs）之类的层状材料是作为可饱和吸收体的极佳候选材料。然而，少层TMDs的可饱和吸收通常是在远离激子共振的激光典型波长下测量的。在这项工作中，我们使用可调谐脉冲激光研究了在A激子共振附近的单层、双层和三层WS₂和WSe₂中的可饱和吸收效应。功率相关的反射率对比度表明，单层WS₂（WSe₂）的饱和功率密度阈值约为5.5×10⁶W/cm²（3.8×10⁶W/cm²），在激子峰值处降低了一个数量级。饱和功率密度阈值随层数增加而增大。动力学方程的解析解说明了激光参数如何影响实验测量的阈值，突出了脉冲持续时间在可饱和吸收中的重要性。这一结果揭示了激子衰减和激子-激子相互作用对TMDs非线性光学性质的影响，有利于基于TMDs的有源光学器件的设计。
