Light from any physical source diffracts over space, as spherical wavefronts grow and energy density is spread out. Diffractive effects pose fundamental limits to light-based technologies, including communications, spectroscopy, and metrology. Polarization becomes paraxial in the far-field limit, and, by ignoring longitudinal field components, the rich physics of non-paraxial fields that exist in near-fields or a beam’s tight focus is lost. The longitudinal field cannot, however, be ignored when transverse field components vanish (in a transverse field zero) and carry a small non-paraxial region to infinity. We show that a transverse field zero is always accompanied by non-diffracting polarization structures, whose geometries are independent of the distance to the source, including an enclosing intensity ratio tube, and parallel, non-diverging polarization singularities. We illustrate these features in multipole radiation and in double-slit interference, two examples that have time-fixed transverse field zeros. Non-diffracting structures with a changing position are coupled to time-varying zeros, which are present in all far-field radiation.

中文翻译：

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电磁辐射远场零点周围的非衍射偏振特征

随着球面波前的增长和能量密度的扩散，来自任何物理源的光都会在空间中衍射。衍射效应对基于光的技术（包括通信、光谱学和计量学）构成了根本限制。偏振在远场极限下变为近轴，并且通过忽略纵向场分量，存在于近场或光束紧聚焦中的非近轴场的丰富物理特性就会丢失。然而，当横向场分量消失（在横向场为零时）并且将小的非近轴区域带到无穷大时，纵向场不能被忽略。我们表明，横向零场总是伴随着非衍射偏振结构，其几何形状与到源的距离无关，包括封闭的强度比管和平行的、非发散的偏振奇点。我们在多极辐射和双缝干涉中说明这些特征，这两个例子具有时间固定的横向场零点。位置变化的非衍射结构与时变零点耦合，这些零点存在于所有远场辐射中。