Wang Pengxiang, Chen Yuntian, Liu Wei
School of Optical and Electronic Information, <a href="https://ror.org/00p991c53">Huazhong University of Science and Technology</a>, Wuhan, Hubei 430074, People's Republic of China.
<a href="https://ror.org/03c9ncn37">Wuhan National Laboratory for Optoelectronics</a>, <a href="https://ror.org/00p991c53">Huazhong University of Science and Technology</a>, Wuhan, Hubei 430074, People's Republic of China.
Phys Rev Lett. 2024 Aug 30;133(9):093801. doi: 10.1103/PhysRevLett.133.093801.
Conventional approaches for scattering manipulations largely rely on the technique of field expansions into spherical harmonics (electromagnetic multipoles), which nevertheless is not only nongeneric (expansion coefficients depend on the origin position of the coordinate system) but also more descriptive than predictive. Here, we explore this classical topic from a different perspective of controlled excitations and interferences of quasinormal modes (QNMs) supported by the scattering system. Scattered waves are expanded into coherent additions of QNMs, among which the relative amplitudes and phases are crucial factors to architect for scattering manipulations. Relying on the electromagnetic reciprocity, we provide full geometric representations based on the Poincaré sphere for those factors, and discover the hidden geometric phase of QNMs that drives the scattering evolutions. Further synchronous exploitations of the incident polarization-dependent geometric phase and excitation amplitudes enable efficient manipulations of both scattering intensities and polarizations. Continuous geometric phase spanning 2π is directly manifest through scattering variations, even in the rather elementary configuration of an individual particle scattering waves of varying polarizations. We have essentially established a profoundly all-encompassing framework for the calculations of geometric phase in arbitrary scattering systems that are reciprocal. Our theoretical model will greatly broaden horizons of many disciplines not only in photonics but also in general wave physics where geometric phase is generic and ubiquitous.
传统的散射操纵方法主要依赖于将场展开为球谐函数（电磁多极子）的技术，然而这种方法不仅不具有通用性（展开系数取决于坐标系的原点位置），而且更多的是描述性而非预测性。在这里，我们从散射系统所支持的准正则模（QNMs）的受控激发和干涉的不同角度来探讨这个经典话题。散射波被展开为准正则模的相干叠加，其中相对振幅和相位是用于散射操纵设计的关键因素。基于电磁互易性，我们为这些因素提供了基于庞加莱球的完整几何表示，并发现了驱动散射演化的准正则模的隐藏几何相位。进一步同步利用与入射偏振相关的几何相位和激发振幅，可以有效地操纵散射强度和偏振。即使在单个粒子散射不同偏振波的相当简单的配置中，跨越2π的连续几何相位也通过散射变化直接体现出来。我们基本上建立了一个用于计算任意互易散射系统中几何相位的深刻而全面的框架。我们的理论模型不仅将极大地拓宽光子学领域，而且还将拓宽一般波动物理学中许多学科的视野，在这些领域中几何相位是普遍存在的。
