Structured light with more extended degrees of freedom (DoFs) and in higher dimensions is increasingly gaining traction and leading to breakthroughs such as super-resolution imaging, larger-capacity communication, and ultraprecise optical trapping or tweezers. More DoFs for manipulating an object can access more maneuvers and radically increase maneuvering precision, which is of significance in biology and related microscopic detection. However, manipulating particles beyond three-dimensional (3D) spatial manipulation by using current all-optical tweezers technology remains difficult. To overcome this limitation, we theoretically and experimentally present six-dimensional (6D) structured optical tweezers based on tailoring structured light emulating rigid-body mechanics. Our method facilitates the evaluation of the methodology of rigid-body mechanics to synthesize six independent DoFs in a structured optical trapping system, akin to six-axis rigid-body manipulation, including surge, sway, heave, roll, pitch, and yaw. In contrast to previous 3D optical tweezers, our 6D structured optical tweezers significantly improved the flexibility of the path design of complex trajectories, thereby laying the foundation for next-generation functional optical manipulation, assembly, and micromechanics.

Structured light fields embody strong spatial variations of polarization, phase, and amplitude. Understanding, characterization, and exploitation of such fields can be achieved through their topological properties. Three-dimensional (3D) topological solitons, such as hopfions, are 3D localized continuous field configurations with nontrivial particle-like structures that exhibit a host of important topologically protected properties. Here, we propose and demonstrate photonic counterparts of hopfions with exact characteristics of Hopf fibration, Hopf index, and Hopf mapping from real-space vector beams to homotopic hyperspheres representing polarization states. We experimentally generate photonic hopfions with on-demand high-order Hopf indices and independently controlled topological textures, including Néel-, Bloch-, and antiskyrmionic types. We also demonstrate a robust free-space transport of photonic hopfions, thus showing the potential of hopfions for developing optical topological informatics and communications.

涡旋光是一种携带轨道角动量、相位面呈螺旋状分布的新型结构光场,在量子纠缠、量子通信、光学微操控等领域已经获得了广泛应用。随着研究的深入,具有比传统涡旋光更复杂的拓扑结构、相位奇点、轨道角动量和偏振奇点的结构光场的产生,吸引了众多研究人员的兴趣。从固体激光腔内直接激发产生空间结构光和腔外调控得到空间结构光出发,分别介绍了离轴泵浦加像散转换、调制元件调制波形、泵浦整形三种腔内方法,以及空间光调制器光场定制、模式叠加、超构表面微结构设计的三种腔外方法,并分析比较了几种方法的优缺点,展望了未来空间涡旋结构光场的发展趋势。

A frequency-degenerate cavity (FDC) is the resonator that the ratio of transverse and longitudinal mode frequency spacings is a simple rational number. When an optical resonator is close to the FDC, transverse-mode-locking (TML) takes place with drastic changes of laser mode. We report for the first time, to the best of our knowledge, the multi-frequency emission and spectral modulation effects coupled with TML in FDC. The Yb:CaGdAlO₄ (Yb:CALGO) crystal with large gain bandwidth was used as a gain medium in an off-axis-pumped hemispherical FDC for realizing broadband emission. Interestingly, the spectrum can transform from a single smooth packet shape to a multi-peak structure; meanwhile, the transverse pattern accordingly transforms into some exotic wave-packet profiles through controlling off-axis displacement in a special degenerate state.

Q-switched operation of an Nd:LuAG laser using gold nanorods (GNRs) as the saturable absorber (SA) is reported, which also produces the highest average power among the nanosecond Nd-doped Q-switched lasers by GNRs-based SA. The applied GNRs are prepared using a seed-mediated growth method and then dropped onto the quartz substrate to fabricate the SA. The average power of the Q-switched laser is 516 mW with the shortest pulse duration of 606.7 ns and the repetition rate of 265.1 kHz.

报道了一种室温条件下工作的高功率激光二极管(LD)端面抽运Yb∶YAG板条双波长激光放大器, 稳定的双波长运转在1029.6, 1031.5 nm。基于Yb∶YAG宽带荧光特性, 建立了双波长放大模型, 通过数值模拟研究了不同抽运条件下激光光谱放大输出特性。通过940 nm激光二极管双端抽运Yb∶YAG晶体, 拥有双波长光谱的种子光从晶体一端注入并进行放大。实验结果表明,在1.18 kW注入时获得了6.56 kW的双波长连续激光输出, 与数值模拟结果相吻合。双波长激光放大理论和实验研究为进一步实现高功率光谱合成等应用奠定了基础。