Topological nodal-line semimetals attract growing research attention in the photonic and optoelectronic fields due to their unique topological energy-level bands and fascinating nonlinear optical responses. Here, to the best of our knowledge, we first report the saturable absorption property of topological nodal-line semimetal HfGeTe and the related pulse modulation in passively Q-switched visible lasers. Few-layer HfGeTe demonstrates outstanding saturable absorption properties in the visible-light band, yielding the saturation intensities of 7.88, 12.66, and 6.64 µJ/cm² at 515, 640, and 720 nm, respectively. Based on an as-prepared few-layer HfGeTe optical switch and a Pr:LiYF₄ gain medium, Q-switched visible lasers are also successfully achieved at 522, 640, and 720 nm. The minimum pulse widths of the green, red, and deep-red pulsed lasers are 150, 125.5, and 420 ns, respectively. Especially for the green and red pulsed laser, the obtained pulse width is smaller than those of the low-dimensional layered materials. Our work sheds light on the application potential of topological nodal-line semimetals in the generation of visible pulsed lasers.

Nonlinear responses of nanoparticles induce enlightening phenomena in optical tweezers. With the gradual increase in optical intensity, effects from saturable absorption (SA) and reverse SA (RSA) arise in sequence and thereby modulate the nonlinear properties of materials. In current nonlinear optical traps, however, the underlying physical mechanism is mainly confined within the SA regime because threshold values required to excite the RSA regime are extremely high. Herein, we demonstrate, both in theory and experiment, nonlinear optical tweezing within the RSA regime, proving that a fascinating composite trapping state is achievable at ultrahigh intensities through an optical force reversal induced through nonlinear absorption. Integrated results help in perfecting the nonlinear optical trapping system, thereby providing beneficial guidance for wider applications of nonlinear optics.

对Sb₂Te₃薄膜的结构、线性光学及非线性吸收性质的Ti掺杂影响进行了系统性探究。利用磁控溅射和高温退火手段制备了不同Ti掺杂浓度的晶态Sb₂Te₃薄膜。X射线光电子能谱分析显示Sb₂Te₃薄膜中的Ti元素以Ti⁴⁺化学态以TiTe₂的形式存在。线性光学性质结果表明，在保持非线性器件中宽工作波长特性的同时，Ti掺杂可以提高Sb₂Te₃薄膜的透射率，并降低光学带隙从1.32 eV至1.25 eV，根据Burstein-Moss理论，这取决于载流子的减少。利用自主搭建的开孔Z扫描系统，测试了薄膜样品在132 GW/cm²强度下800 nm飞秒激光激发的非线性吸收性质，结果显示的Ti掺杂引起的饱和吸收可调谐行为可归因于光学带隙减小与晶化抑制的竞争效应。此外，Ti掺杂将Sb₂Te₃薄膜的激光损伤阈值从188.6 GW/cm²提高到了265.5 GW/cm²。总而言之，Ti掺杂Sb₂Te₃薄膜在非线性光学器件领域具有广泛的应用前景。

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。