Dipartimento di Fisica, Università di Napoli Federico II, Complesso Universitario di Monte Sant'Angelo, Napoli, Italy.
CNR-SPIN, Complesso Universitario di Monte Sant'Angelo, Napoli, Italy.
Sci Rep. 2017 Jan 12;7:40195. doi: 10.1038/srep40195.
Optical singularities manifesting at the center of vector vortex beams are unstable, since their topological charge is higher than the lowest value permitted by Maxwell's equations. Inspired by conceptually similar phenomena occurring in the polarization pattern characterizing the skylight, we show how perturbations that break the symmetry of radially symmetric vector beams lead to the formation of a pair of fundamental and stable singularities, i.e. points of circular polarization. We prepare a superposition of a radial (or azimuthal) vector beam and a uniformly linearly polarized Gaussian beam; by varying the amplitudes of the two fields, we control the formation of pairs of these singular points and their spatial separation. We complete this study by applying the same analysis to vector vortex beams with higher topological charges, and by investigating the features that arise when increasing the intensity of the Gaussian term. Our results can find application in the context of singularimetry, where weak fields are measured by considering them as perturbations of unstable optical beams.
中心处呈现的光学奇点在矢量涡旋光束中是不稳定的，因为它们的拓扑电荷高于麦克斯韦方程组允许的最低值。受启发于自然光的偏振模式中出现的类似现象，我们展示了如何打破具有径向对称的矢量光束的对称性的微扰会导致形成一对基本且稳定的奇点，即圆偏振点。我们制备了径向（或角向）矢量光束和均匀线偏振高斯光束的叠加；通过改变两个场的振幅，我们控制了这些奇异点对的形成及其空间分离。我们通过将相同的分析应用于具有更高拓扑电荷的矢量涡旋光束，并研究了增加高斯项强度时出现的特征，完成了这项研究。我们的结果可应用于奇点测量学中，通过将弱场视为不稳定光束的微扰来测量它们。
