采用化学气相沉积法制备了直立生长的SnS₂（V-SnS₂）薄膜，并使用自主搭建的Z扫描系统研究了V-SnS₂的三阶非线性光学响应。结果表明，由于S空位的存在使得V-SnS₂薄膜表现出明显的饱和吸收响应，且非线性吸收系数（β）随着泵浦功率的增加而减少。分析发现，其β的最大值为6 cm/GW，调制深度（ΔM）为50%。同时，通过闭口Z扫描技术测量发现V-SnS₂薄膜的n₂比Si和GaAs大一个数量级，且n₂随着泵浦功率的增加而减少，基于自由载流子的非线性理论分析表明这与材料中的自由载流子和束缚电子密切相关。本文研究证明V-SnS₂在全光开关、激光调Q等非线性光电子器件的设计与制造方面有潜在的应用。

利用液相剥离法制备了WS₂纳米片，结合真空抽滤技术，控制上清液体积制备了不同厚度的WS₂薄膜。在此基础上，使用800 nm飞秒激光的Z扫描技术表征了WS₂纳米薄膜的三阶非线性吸收特性。研究发现，制备的不同厚度的WS₂都表现出可饱和吸收特性，可饱和吸收主要是由于单光子吸收所引起的泡利阻塞效应引起；随着厚度的增加，饱和强度基本不变，调制深度会有所提高，但是三阶非线性极化率虚部的绝对值和品质因子会降低。这主要是因为较厚的薄膜缺陷更多，更容易捕获光生载流子，从而三阶非线性吸收和厚度有一定的依赖关系。可饱和吸收可以用于调Q激光器以及锁模激光器，为WS₂薄膜在超快开关和超快激光的应用提供实验支持。

通过太赫兹发射光谱研究了400 nm飞秒激光脉冲激发层状MoSe₂所引起的物理效应。太赫兹振幅随泵浦功率、方位角、偏振角的依赖关系表明，太赫兹辐射主要由表面耗尽场诱导的光生电流和二阶非线性极化诱导的移位电流这两种瞬态光电流效应共同引起，并且两种电流的贡献分别为82%和18%。研究结果可为MoSe₂在超快光学领域的发展和应用提供实验支持。

Understanding and controlling defect in two-dimensional materials is important for both linear and nonlinear optoelectronic devices, especially in terms of tuning nonlinear optical absorption. Taking advantage of an atomic defect formed easily by smaller size, molybdenum disulfide nanosheet is prepared successfully with a different size by gradient centrifugation. Interestingly, size-dependent sulfur vacancies are observed by high-resolution X-ray photoelectron spectroscopy, atomic force microscopy, and transmission electron microscopy. The defect effect on nonlinear absorption is investigated by Z-scan measurement at the wavelength of 800 nm. The results suggest the transition from saturable absorption to reverse saturable absorption can be observed in both dispersions and films. First principle calculations suggest that sulfur vacancies act as the trap state to capture the excited electrons. Moreover, an energy-level model with the trap state is put forward to explain the role of the sulfur vacancy defect in nonlinear optical absorption. The results suggest that saturable absorption and reverse saturable absorption originate from the competition between the excited, defect state and ground state absorption. Our finding provides a way to tune the nonlinear optical performance of optoelectronic devices by defect engineering.

The prominent third-order nonlinear optical properties of WTe2 films are studied through the Z-scan technique using a femtosecond pulsed laser at 1030 nm. Open-aperture (OA) and closed-aperture (CA) Z-scan measurements are performed at different intensities to investigate the nonlinear absorption and refraction properties of WTe2 films. OA Z-scan results show that WTe2 films always hold a saturable absorption characteristic without transition to reverse saturable absorption. Further, a large nonlinear absorption coefficient β is determined to be 3.37×103cm/GW by fitting the OA Z-scan curve at the peak intensity of 15.603GW/cm2. In addition, through the slow saturation absorption model, the ground state absorption cross section, excited state absorption cross section, and absorber’s density were found to be 1.4938×10 16cm2, 1.2536×10 16cm2, and 6.2396×1020cm 3, respectively. CA Z-scan results exhibit a classic peak–valley shape of the CA Z-scan signal, which reveals a self-defocusing optical effect of WTe2 films under the measured environment. Furthermore, a considerable nonlinear refractive index value n2 can be obtained at 1.629×10 2cm2/GW. Ultimately, the values of the real and imaginary parts of the third-order nonlinear s