近日，美国国家加速器实验室Jenny Morgan团队研究了自由电子激光器的庞加莱光束。相关论文于2025年8月13日发表在《自然—光子学》杂志上。
庞加莱光束是具有空间非均匀偏振结构的光束，它跨越了庞加莱球的有限部分。这一特性赋予了光束有趣的拓扑特性，并导致了对其基本特性，控制产生和新兴应用的研究激增。
研究组介绍了在费米自由电子激光器（FEL）上产生的极紫外（16.7nm）庞加莱光束的实验演示。“星”型庞加莱光束是利用FEL辐射固有的相位和强度结构产生的，而不依赖于光学元件。研究组通过精确的重叠和功率平衡来控制空间偏振分布，每个脉冲具有不同的横向相位分布和正交圆偏振。对空间极化结构进行了详细的映射，显示了庞加莱球的广泛覆盖范围，与分析预测一致。这种在FELs中原位生产庞加莱光束的方法可以在偏振态的方向和平衡上实现直接的灵活性，并且可以很容易地扩展到其他矢量光束和更短的波长，从而在现代光环境中实现新的科学应用。
附：英文原文
Title: Poincaré beams from a free electron laser
Author: Morgan, Jenny, Rebernik Ribi, Primo, Capotondi, Flavio, Brynes, Alexander, Manfredda, Michele, De Ninno, Giovanni, Novinec, Luka, Pancaldi, Matteo, Pedersoli, Emanuele, Simoncig, Alberto, Spezzani, Carlo, Zangrando, Marco, Hemsing, Erik
Issue&Volume: 2025-08-13
Abstract: Poincaré beams are light beams that have spatially inhomogeneous polarization structure that spans a finite portion of the Poincaré sphere. This feature bestows the beams with intriguing topological properties and has led to a surge in research on their fundamental characteristics, their controlled generation and on emerging applications. Here we present an experimental demonstration of a Poincaré beam generated in the extreme ultraviolet (16.7nm) at the FERMI free electron laser (FEL). The ‘star’ type Poincaré beam is generated by exploiting the phase and intensity structure intrinsic to FEL radiation without relying on optical elements. We controlled the spatial polarization distribution through a precise overlap and power balance between two FEL pulses, each with different transverse phase distributions and orthogonal circular polarizations. The spatial polarization structure was mapped in detail and shows extensive coverage of the Poincaré sphere, in agreement with analytic predictions. This method of in situ Poincaré beam production in FELs enables straightforward flexibility in the orientation and balance of polarization states, and can readily be extended to other vector beams and to shorter wavelengths enabling novel science applications in modern light sources.
DOI: 10.1038/s41566-025-01737-7
Source: https://www.nature.com/articles/s41566-025-01737-7